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Re: [loopantennas] Wellbrook ALA1530

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  • gandalfg8@aol.com
    In a message dated 04/05/2007 04:19:30 GMT Daylight Time, nonlinear@rogers.com writes: must have some good vhf jfets in there Why? [Non-text portions of this
    Message 1 of 28 , May 5, 2007
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      In a message dated 04/05/2007 04:19:30 GMT Daylight Time,
      nonlinear@... writes:

      must have some good vhf jfets in there


      Why?






      [Non-text portions of this message have been removed]
    • gandalfg8@aol.com
      In a message dated 04/05/2007 04:36:52 GMT Daylight Time, nonlinear@rogers.com writes: or mosfets Again....why? [Non-text portions of this message have been
      Message 2 of 28 , May 5, 2007
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        In a message dated 04/05/2007 04:36:52 GMT Daylight Time,
        nonlinear@... writes:

        or mosfets


        Again....why?






        [Non-text portions of this message have been removed]
      • Paul Birke
        Dear Nigel highest gain and lowest noise more likely with jfets ie more likely in the design than bipolar although not necessarily true if one considers say
        Message 3 of 28 , May 5, 2007
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          Dear Nigel

          highest gain and lowest noise more likely with jfets

          ie more likely in the design than bipolar although not necessarily true if one considers say the David Norton noiseless design with bipolar

          however the Norton design is limited to smaller gains

          best
          Paul

          ----- Original Message ----
          From: "gandalfg8@..." <gandalfg8@...>
          To: loopantennas@yahoogroups.com
          Sent: Saturday, May 5, 2007 5:21:00 AM
          Subject: Re: [loopantennas] Wellbrook ALA1530















          In a message dated 04/05/2007 04:19:30 GMT Daylight Time,

          nonlinear@rogers. com writes:



          must have some good vhf jfets in there



          Why?



          [Non-text portions of this message have been removed]














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        • Paul Birke
          N there are some mosfet designs that have very low noise with moderate gain for instance my H-900 has low noise reasonable gain mosfet design in the end it is
          Message 4 of 28 , May 5, 2007
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            N
            there are some mosfet designs that have very low noise with moderate gain for instance my H-900 has low noise reasonable gain mosfet design

            in the end it is a choice of course but the jfets and mosfets have gained more use in the active antenna amplifiers again with the caveat that the Norton would if used use bipolar re Dallas Lankford

            P

            ----- Original Message ----
            From: "gandalfg8@..." <gandalfg8@...>
            To: loopantennas@yahoogroups.com
            Sent: Saturday, May 5, 2007 5:21:22 AM
            Subject: Re: [loopantennas] Wellbrook ALA1530















            In a message dated 04/05/2007 04:36:52 GMT Daylight Time,

            nonlinear@rogers. com writes:



            or mosfets



            Again....why?



            [Non-text portions of this message have been removed]














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          • gandalfg8@aol.com
            In a message dated 05/05/2007 17:28:55 GMT Daylight Time, nonlinear@rogers.com writes: highest gain and lowest noise more likely with jfets ie more likely in
            Message 5 of 28 , May 5, 2007
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              In a message dated 05/05/2007 17:28:55 GMT Daylight Time,
              nonlinear@... writes:

              highest gain and lowest noise more likely with jfets

              ie more likely in the design than bipolar although not necessarily true if
              one considers say the David Norton noiseless design with bipolar

              however the Norton design is limited to smaller gains


              ---------------------------------------------------------
              "Is more likely" is a bit different to the earlier "must have".

              I was just intrigued as to your reasoning, considering that the hardware
              content of a dismembered 1530 was discussed here in some detail only a few weeks
              ago and the active devices were obviously bipolar.

              regards

              Nigel
              GM8PZR






              [Non-text portions of this message have been removed]
            • Paul Birke
              Dear Nigel forgot that getting old, I remember that now, I remember seeing the pictures but was fuzzy on whether for sure bipolars were used I believe it was
              Message 6 of 28 , May 5, 2007
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                Dear Nigel

                forgot that getting old, I remember that now, I remember seeing the pictures but was fuzzy on whether for sure bipolars were used

                I believe it was not known from the autopsy whether it was a Norton design or not

                otherwise it is likely a push pull grounded base design for low noise and wide bandwidth

                what do you think?

                was there a schematic ever published for the Wellbrook

                best
                Paul

                ----- Original Message ----
                From: "gandalfg8@..." <gandalfg8@...>
                To: loopantennas@yahoogroups.com
                Sent: Saturday, May 5, 2007 12:36:40 PM
                Subject: Re: [loopantennas] Wellbrook ALA1530















                In a message dated 05/05/2007 17:28:55 GMT Daylight Time,

                nonlinear@rogers. com writes:



                highest gain and lowest noise more likely with jfets



                ie more likely in the design than bipolar although not necessarily true if

                one considers say the David Norton noiseless design with bipolar



                however the Norton design is limited to smaller gains



                ------------ --------- --------- --------- --------- ---------

                "Is more likely" is a bit different to the earlier "must have".



                I was just intrigued as to your reasoning, considering that the hardware

                content of a dismembered 1530 was discussed here in some detail only a few weeks

                ago and the active devices were obviously bipolar.



                regards



                Nigel

                GM8PZR



                [Non-text portions of this message have been removed]














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              • crabtreejr@aol.com
                Hello Nigel, Paul et al AFAIK no schematics for the Wellbrook have ever been published. However the harware content which was discussed here, and other
                Message 7 of 28 , May 5, 2007
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                  Hello Nigel, Paul et al

                  AFAIK no schematics for the Wellbrook have ever been published. However the
                  harware content which was discussed here, and other information, leads me to
                  the conclusion that the amplifier is a push pull grounded base design, as Paul
                  suggests.

                  It is not that difficult to work out a possible configuration, as follows:

                  1. Basic physics of a small loop

                  The basic physics of a small receiving loop is well understood (see eg
                  Jasik's Antenna Engineering Handbook, 1st ed, 1961, p 6-2)

                  The unloaded voltage induced in a loop antena =
                  2.Pi.A.N.E.Sin(theta) / Lambda
                  where
                  Pi = 3.14
                  A = the area of the loop
                  N = the number of turns
                  E = the electric field strength
                  theta = the angle measured from the axis of the loop
                  lambda = the wavelength

                  Let us simplify this, assuming that N = 1, and theta = 90 degrees. Let us
                  also replace Lambda by c/f where c = the speed of light, and f = the frequency.
                  Then
                  V = 2.Pi.A.E.f / c

                  It can readily seen that for a constant field strength E, that the voltage
                  ouput is proportional to frequency. There is a simple method to overcome this
                  difficulty.

                  The untuned receiving loop can be considered as a voltage source in series
                  with the radiation resistance (very small, ie a small fraction of an ohm), the
                  loss resistance (probably somewhat larger), and the inductance of the loop,
                  which is the largest component. Take for example a (Wellbrook) loop with a
                  diameter of 1 meter, and a tube diameter of 25mm. Then the the inductance (L) is
                  ca. 2.33uH, with an impedance of ca. 14.6 ohms at 1MHz.

                  If one terminates the loop in an impedance in a resistance (R) much lower
                  than the inductance, then the current output is determined by the inductance, and
                  equals
                  V / (2.Pi.f.L) = (A.E) / (c.L)
                  which is frequency independent

                  Then the power output from the loop is i.i.R
                  = (A.A.E.E.R) / (c.c.L.L)
                  which is again frequency independent.

                  As the frequency goes down, the ouput goes down for constant E, with the -3dB
                  frequency equalling
                  1 / 2.Pi.L.R

                  2. Loop termination resistance for a ALA1530

                  To determine an approximate value for R, it is necessary to look at the
                  performance figures of a Wellbrook loop. Fortunately, there are performance
                  figures for an ALA1530 on the Wellbrook web site. Looking at the numbers the -3dB
                  frequency is ca. 550kHz, which would give an R of ca. 8.1 ohms.

                  It is that simple - terminate a one meter loop with a resistance of ca. 8
                  ohms, and you will get approximately the frequency response performance of an
                  ALA1530. Clearly the response falls away at very low and very high frequencies,
                  but that is probably due to various transformer effects.

                  3. Amplifier gain for a ALA1530

                  We must now consider the amplifier gain. Assuming a unity antenna factor, ie
                  one volt out for a field strength of 1 Volt per meter, then the gain required
                  is
                  power out / power in
                  Assuming the ouptut load is 50 ohms, then the required gain
                  = (c.c.L.L) / (A.A.R.50)

                  Sticking in the numbers which we already have, I calculated that for a unity
                  antenna factor, that the gain required would be ca. 33dB. The actual antenna
                  factor is ca. -7dB, and so the required gain is ca. 26dB.

                  To recap, we know know that to duplicate a ALA1530, we would need an
                  amplifier with an input impedance of ca. 8 ohms, and a gain of ca. 26dB.

                  4. Amplifier configuration

                  Assuming that the ALA1530 uses two transistors in its push-pull amplifier,
                  then the only way to do is through a common base amplifier with a transformer
                  coupled input and output. A Norton amplifier would not have sufficient gain.
                  It should be remembered that the input resistance of a Norton amplifier depends
                  upon the output load, which we do not want in this case.

                  The small signal input resistance of a common base amplifier is ca. 26mV
                  divided by the emitter current. To get some good linearity, a high quiescent
                  current is essential. Removing the heat from the transistors has to be
                  considered.

                  Let us assume that pretty much all of the stated 120mA supply current goes to
                  the two transistors, ie ca. 50-60mA each. Then the input resistance of each
                  transistor at 60mA bias is ca. 0.43 ohms. The two are effectively in series
                  and so the total input resistance is ca. 0.86 ohms.

                  The required turns ratio of the input transformer is SQRT( 8 / 0.86) = 3.04.
                  This is conveniently very close to 3.0, which is what you would wind. This
                  means that the transformer can be wound with a trifilar winding.

                  The amplifer gain effectively is approximately the output load resistance
                  divided by the input resistance. We need a gain of ca. 26dB, ie ca. 400.

                  Assume that the gain is 27dB, ie 500. The the required output resistance is
                  500 x 0.86 = 430 ohms. Assuming that the transformed output load is 50 ohms,
                  this would give a turns ratio on the output transformer of 2.93, ie very close
                  to 3.0, which could also easily be wound with a trifilar winding.

                  My conlusion is that a push-pull amplifier with the transistors each biassed
                  at ca. 50-60mA, and a 3:1 step down transformer on the input and output would
                  work give approximately the measured performance of the ALA1530. This should
                  be a fairly straightforward amplifier, if some attention is paid to the
                  detail. 2N5109 transistors should work quite well. There are, of course, other
                  choices.

                  5. Observations

                  Many people have wondered how the broadband matching was done in the ALA1530.
                  It is simply done by having an amplifier with a constant input impedance
                  lower than the inductive reactance of the loop at frequencies for which a
                  constant gain is desired.

                  Many people have thought that the amplifier must in some way be exotic. I
                  suggest that it is actually fairly simple, and that this might be the reason for
                  potting it.

                  Later versions of the ALA1530 have an amplifier with better intermodulation
                  performance. They also have a higher quiescent current, and a higher gain.
                  This suggests to me that there are more transistors, probably in a two stage
                  push-pull amplifier.

                  There was a broadband loop available in the UK before the Wellbrook ALA1530
                  was introduced. It was designed by Edward Forster, and sold by his company -
                  Phase Track Ltd, which was based in Reading. His patent - GB2235337 - gives
                  some useful background on broadband loop antennas and their amplifiers.

                  Finally, broadband loop antenas are a compromise solution. At lower
                  frequencies, the radiation resistance is very low, and hence they are very
                  inefiicient. This means that you will not be able to hear signals near the noise floor.
                  Of course, they do appear to offer better noise rejection than an active rod
                  antenna, unless you are very careful (eg see some of Dallas Lankford's recent
                  writings). They are also convenient, and can offer some directionality.

                  HTH and 73

                  John KC0G


                  In a message dated 5/5/07 12:28:19 PM Central Daylight Time,
                  nonlinear@... writes:
                  > Dear Nigel
                  >
                  > forgot that getting old, I remember that now, I remember seeing the pictures
                  > but was fuzzy on whether for sure bipolars were used
                  >
                  > I believe it was not known from the autopsy whether it was a Norton design
                  > or not
                  > otherwise it is likely a push pull grounded base design for low noise and
                  > wide bandwidth
                  >
                  > what do you think?
                  >
                  > was there a schematic ever published for the Wellbrook
                  >
                  > best
                  > Paul
                  >
                  > ----- Original Message ----
                  > From: "gandalfg8@..." <gandalfg8@...>
                  > To: loopantennas@yahoogroups.com
                  > Sent: Saturday, May 5, 2007 12:36:40 PM
                  > Subject: Re: [loopantennas] Wellbrook ALA1530
                  >
                  > In a message dated 05/05/2007 17:28:55 GMT Daylight Time,
                  >
                  > nonlinear@rogers. com writes:
                  >
                  > highest gain and lowest noise more likely with jfets
                  > ie more likely in the design than bipolar although not necessarily true if
                  > one considers say the David Norton noiseless design with bipolar
                  > however the Norton design is limited to smaller gains
                  >
                  > ------------ --------- --------- --------- --------- ---------
                  >
                  > "Is more likely" is a bit different to the earlier "must have".
                  > I was just intrigued as to your reasoning, considering that the hardware
                  > content of a dismembered 1530 was discussed here in some detail only a few
                  > weeks
                  > ago and the active devices were obviously bipolar.
                  >
                  > regards
                  > Nigel
                  > GM8PZR
                  >


                  **************************************
                  See what's free at http://www.aol.com
                  >


                  [Non-text portions of this message have been removed]
                • Paul Birke
                  Dear John trying to follow most of your excellent expose via backward analysis however the voltage gain is 20 logbase10 (V2/V1) so for 27 dB we have
                  Message 8 of 28 , May 5, 2007
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                    Dear John

                    trying to follow most of your excellent expose via backward analysis

                    however the voltage gain is 20 logbase10 (V2/V1)

                    so for 27 dB we have 10^(27/20)=22.4 actual voltage ratio emitter to collector

                    there is now way a single grounded base can produce your 500 voltage gain but it can hit ~22

                    if wrong above what I am missing?

                    best wishes
                    Paul V Birke PEng
                    Guelph ON

                    ----- Original Message ----
                    From: "crabtreejr@..." <crabtreejr@...>
                    To: loopantennas@yahoogroups.com
                    Sent: Saturday, May 5, 2007 9:09:04 PM
                    Subject: Re: [loopantennas] Wellbrook ALA1530













                    Hello Nigel, Paul et al



                    AFAIK no schematics for the Wellbrook have ever been published. However the

                    harware content which was discussed here, and other information, leads me to

                    the conclusion that the amplifier is a push pull grounded base design, as Paul

                    suggests.



                    It is not that difficult to work out a possible configuration, as follows:



                    1. Basic physics of a small loop



                    The basic physics of a small receiving loop is well understood (see eg

                    Jasik's Antenna Engineering Handbook, 1st ed, 1961, p 6-2)



                    The unloaded voltage induced in a loop antena =

                    2.Pi.A.N.E.Sin( theta) / Lambda

                    where

                    Pi = 3.14

                    A = the area of the loop

                    N = the number of turns

                    E = the electric field strength

                    theta = the angle measured from the axis of the loop

                    lambda = the wavelength



                    Let us simplify this, assuming that N = 1, and theta = 90 degrees. Let us

                    also replace Lambda by c/f where c = the speed of light, and f = the frequency.

                    Then

                    V = 2.Pi.A.E.f / c



                    It can readily seen that for a constant field strength E, that the voltage

                    ouput is proportional to frequency. There is a simple method to overcome this

                    difficulty.



                    The untuned receiving loop can be considered as a voltage source in series

                    with the radiation resistance (very small, ie a small fraction of an ohm), the

                    loss resistance (probably somewhat larger), and the inductance of the loop,

                    which is the largest component. Take for example a (Wellbrook) loop with a

                    diameter of 1 meter, and a tube diameter of 25mm. Then the the inductance (L) is

                    ca. 2.33uH, with an impedance of ca. 14.6 ohms at 1MHz.



                    If one terminates the loop in an impedance in a resistance (R) much lower

                    than the inductance, then the current output is determined by the inductance, and

                    equals

                    V / (2.Pi.f.L) = (A.E) / (c.L)

                    which is frequency independent



                    Then the power output from the loop is i.i.R

                    = (A.A.E.E.R) / (c.c.L.L)

                    which is again frequency independent.



                    As the frequency goes down, the ouput goes down for constant E, with the -3dB

                    frequency equalling

                    1 / 2.Pi.L.R



                    2. Loop termination resistance for a ALA1530



                    To determine an approximate value for R, it is necessary to look at the

                    performance figures of a Wellbrook loop. Fortunately, there are performance

                    figures for an ALA1530 on the Wellbrook web site. Looking at the numbers the -3dB

                    frequency is ca. 550kHz, which would give an R of ca. 8.1 ohms.



                    It is that simple - terminate a one meter loop with a resistance of ca. 8

                    ohms, and you will get approximately the frequency response performance of an

                    ALA1530. Clearly the response falls away at very low and very high frequencies,

                    but that is probably due to various transformer effects.



                    3. Amplifier gain for a ALA1530



                    We must now consider the amplifier gain. Assuming a unity antenna factor, ie

                    one volt out for a field strength of 1 Volt per meter, then the gain required

                    is

                    power out / power in

                    Assuming the ouptut load is 50 ohms, then the required gain

                    = (c.c.L.L) / (A.A.R.50)



                    Sticking in the numbers which we already have, I calculated that for a unity

                    antenna factor, that the gain required would be ca. 33dB. The actual antenna

                    factor is ca. -7dB, and so the required gain is ca. 26dB.



                    To recap, we know know that to duplicate a ALA1530, we would need an

                    amplifier with an input impedance of ca. 8 ohms, and a gain of ca. 26dB.



                    4. Amplifier configuration



                    Assuming that the ALA1530 uses two transistors in its push-pull amplifier,

                    then the only way to do is through a common base amplifier with a transformer

                    coupled input and output. A Norton amplifier would not have sufficient gain.

                    It should be remembered that the input resistance of a Norton amplifier depends

                    upon the output load, which we do not want in this case.



                    The small signal input resistance of a common base amplifier is ca. 26mV

                    divided by the emitter current. To get some good linearity, a high quiescent

                    current is essential. Removing the heat from the transistors has to be

                    considered.



                    Let us assume that pretty much all of the stated 120mA supply current goes to

                    the two transistors, ie ca. 50-60mA each. Then the input resistance of each

                    transistor at 60mA bias is ca. 0.43 ohms. The two are effectively in series

                    and so the total input resistance is ca. 0.86 ohms.



                    The required turns ratio of the input transformer is SQRT( 8 / 0.86) = 3.04.

                    This is conveniently very close to 3.0, which is what you would wind. This

                    means that the transformer can be wound with a trifilar winding.



                    The amplifer gain effectively is approximately the output load resistance

                    divided by the input resistance. We need a gain of ca. 26dB, ie ca. 400.



                    Assume that the gain is 27dB, ie 500. The the required output resistance is

                    500 x 0.86 = 430 ohms. Assuming that the transformed output load is 50 ohms,

                    this would give a turns ratio on the output transformer of 2.93, ie very close

                    to 3.0, which could also easily be wound with a trifilar winding.



                    My conlusion is that a push-pull amplifier with the transistors each biassed

                    at ca. 50-60mA, and a 3:1 step down transformer on the input and output would

                    work give approximately the measured performance of the ALA1530. This should

                    be a fairly straightforward amplifier, if some attention is paid to the

                    detail. 2N5109 transistors should work quite well. There are, of course, other

                    choices.



                    5. Observations



                    Many people have wondered how the broadband matching was done in the ALA1530.

                    It is simply done by having an amplifier with a constant input impedance

                    lower than the inductive reactance of the loop at frequencies for which a

                    constant gain is desired.



                    Many people have thought that the amplifier must in some way be exotic. I

                    suggest that it is actually fairly simple, and that this might be the reason for

                    potting it.



                    Later versions of the ALA1530 have an amplifier with better intermodulation

                    performance. They also have a higher quiescent current, and a higher gain.

                    This suggests to me that there are more transistors, probably in a two stage

                    push-pull amplifier.



                    There was a broadband loop available in the UK before the Wellbrook ALA1530

                    was introduced. It was designed by Edward Forster, and sold by his company -

                    Phase Track Ltd, which was based in Reading. His patent - GB2235337 - gives

                    some useful background on broadband loop antennas and their amplifiers.



                    Finally, broadband loop antenas are a compromise solution. At lower

                    frequencies, the radiation resistance is very low, and hence they are very

                    inefiicient. This means that you will not be able to hear signals near the noise floor.

                    Of course, they do appear to offer better noise rejection than an active rod

                    antenna, unless you are very careful (eg see some of Dallas Lankford's recent

                    writings). They are also convenient, and can offer some directionality.



                    HTH and 73



                    John KC0G



                    In a message dated 5/5/07 12:28:19 PM Central Daylight Time,

                    nonlinear@rogers. com writes:

                    > Dear Nigel

                    >

                    > forgot that getting old, I remember that now, I remember seeing the pictures

                    > but was fuzzy on whether for sure bipolars were used

                    >

                    > I believe it was not known from the autopsy whether it was a Norton design

                    > or not

                    > otherwise it is likely a push pull grounded base design for low noise and

                    > wide bandwidth

                    >

                    > what do you think?

                    >

                    > was there a schematic ever published for the Wellbrook

                    >

                    > best

                    > Paul

                    >

                    > ----- Original Message ----

                    > From: "gandalfg8@aol. com" <gandalfg8@aol. com>

                    > To: loopantennas@ yahoogroups. com

                    > Sent: Saturday, May 5, 2007 12:36:40 PM

                    > Subject: Re: [loopantennas] Wellbrook ALA1530

                    >

                    > In a message dated 05/05/2007 17:28:55 GMT Daylight Time,

                    >

                    > nonlinear@rogers. com writes:

                    >

                    > highest gain and lowest noise more likely with jfets

                    > ie more likely in the design than bipolar although not necessarily true if

                    > one considers say the David Norton noiseless design with bipolar

                    > however the Norton design is limited to smaller gains

                    >

                    > ------------ --------- --------- --------- --------- ---------

                    >

                    > "Is more likely" is a bit different to the earlier "must have".

                    > I was just intrigued as to your reasoning, considering that the hardware

                    > content of a dismembered 1530 was discussed here in some detail only a few

                    > weeks

                    > ago and the active devices were obviously bipolar.

                    >

                    > regards

                    > Nigel

                    > GM8PZR

                    >



                    ************ ********* ********* ********

                    See what's free at http://www.aol com.

                    >



                    [Non-text portions of this message have been removed]














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                    [Non-text portions of this message have been removed]
                  • Paul Birke
                    Dear John ok you are referring to Power Gain = 10 logbase10 (P2/P1) which is defined via the antenna terminology so everything is in terms of power gain ok
                    Message 9 of 28 , May 5, 2007
                    • 0 Attachment
                      Dear John

                      ok you are referring to Power Gain = 10 logbase10 (P2/P1) which is defined via the antenna terminology so everything is in terms of power gain

                      ok forgot some of my limited antenna theory LOL

                      best
                      Paul



                      ----- Original Message ----
                      From: "crabtreejr@..." <crabtreejr@...>
                      To: loopantennas@yahoogroups.com
                      Sent: Saturday, May 5, 2007 9:09:04 PM
                      Subject: Re: [loopantennas] Wellbrook ALA1530













                      Hello Nigel, Paul et al



                      AFAIK no schematics for the Wellbrook have ever been published. However the

                      harware content which was discussed here, and other information, leads me to

                      the conclusion that the amplifier is a push pull grounded base design, as Paul

                      suggests.



                      It is not that difficult to work out a possible configuration, as follows:



                      1. Basic physics of a small loop



                      The basic physics of a small receiving loop is well understood (see eg

                      Jasik's Antenna Engineering Handbook, 1st ed, 1961, p 6-2)



                      The unloaded voltage induced in a loop antena =

                      2.Pi.A.N.E.Sin( theta) / Lambda

                      where

                      Pi = 3.14

                      A = the area of the loop

                      N = the number of turns

                      E = the electric field strength

                      theta = the angle measured from the axis of the loop

                      lambda = the wavelength



                      Let us simplify this, assuming that N = 1, and theta = 90 degrees. Let us

                      also replace Lambda by c/f where c = the speed of light, and f = the frequency.

                      Then

                      V = 2.Pi.A.E.f / c



                      It can readily seen that for a constant field strength E, that the voltage

                      ouput is proportional to frequency. There is a simple method to overcome this

                      difficulty.



                      The untuned receiving loop can be considered as a voltage source in series

                      with the radiation resistance (very small, ie a small fraction of an ohm), the

                      loss resistance (probably somewhat larger), and the inductance of the loop,

                      which is the largest component. Take for example a (Wellbrook) loop with a

                      diameter of 1 meter, and a tube diameter of 25mm. Then the the inductance (L) is

                      ca. 2.33uH, with an impedance of ca. 14.6 ohms at 1MHz.



                      If one terminates the loop in an impedance in a resistance (R) much lower

                      than the inductance, then the current output is determined by the inductance, and

                      equals

                      V / (2.Pi.f.L) = (A.E) / (c.L)

                      which is frequency independent



                      Then the power output from the loop is i.i.R

                      = (A.A.E.E.R) / (c.c.L.L)

                      which is again frequency independent.



                      As the frequency goes down, the ouput goes down for constant E, with the -3dB

                      frequency equalling

                      1 / 2.Pi.L.R



                      2. Loop termination resistance for a ALA1530



                      To determine an approximate value for R, it is necessary to look at the

                      performance figures of a Wellbrook loop. Fortunately, there are performance

                      figures for an ALA1530 on the Wellbrook web site. Looking at the numbers the -3dB

                      frequency is ca. 550kHz, which would give an R of ca. 8.1 ohms.



                      It is that simple - terminate a one meter loop with a resistance of ca. 8

                      ohms, and you will get approximately the frequency response performance of an

                      ALA1530. Clearly the response falls away at very low and very high frequencies,

                      but that is probably due to various transformer effects.



                      3. Amplifier gain for a ALA1530



                      We must now consider the amplifier gain. Assuming a unity antenna factor, ie

                      one volt out for a field strength of 1 Volt per meter, then the gain required

                      is

                      power out / power in

                      Assuming the ouptut load is 50 ohms, then the required gain

                      = (c.c.L.L) / (A.A.R.50)



                      Sticking in the numbers which we already have, I calculated that for a unity

                      antenna factor, that the gain required would be ca. 33dB. The actual antenna

                      factor is ca. -7dB, and so the required gain is ca. 26dB.



                      To recap, we know know that to duplicate a ALA1530, we would need an

                      amplifier with an input impedance of ca. 8 ohms, and a gain of ca. 26dB.



                      4. Amplifier configuration



                      Assuming that the ALA1530 uses two transistors in its push-pull amplifier,

                      then the only way to do is through a common base amplifier with a transformer

                      coupled input and output. A Norton amplifier would not have sufficient gain.

                      It should be remembered that the input resistance of a Norton amplifier depends

                      upon the output load, which we do not want in this case.



                      The small signal input resistance of a common base amplifier is ca. 26mV

                      divided by the emitter current. To get some good linearity, a high quiescent

                      current is essential. Removing the heat from the transistors has to be

                      considered.



                      Let us assume that pretty much all of the stated 120mA supply current goes to

                      the two transistors, ie ca. 50-60mA each. Then the input resistance of each

                      transistor at 60mA bias is ca. 0.43 ohms. The two are effectively in series

                      and so the total input resistance is ca. 0.86 ohms.



                      The required turns ratio of the input transformer is SQRT( 8 / 0.86) = 3.04.

                      This is conveniently very close to 3.0, which is what you would wind. This

                      means that the transformer can be wound with a trifilar winding.



                      The amplifer gain effectively is approximately the output load resistance

                      divided by the input resistance. We need a gain of ca. 26dB, ie ca. 400.



                      Assume that the gain is 27dB, ie 500. The the required output resistance is

                      500 x 0.86 = 430 ohms. Assuming that the transformed output load is 50 ohms,

                      this would give a turns ratio on the output transformer of 2.93, ie very close

                      to 3.0, which could also easily be wound with a trifilar winding.



                      My conlusion is that a push-pull amplifier with the transistors each biassed

                      at ca. 50-60mA, and a 3:1 step down transformer on the input and output would

                      work give approximately the measured performance of the ALA1530. This should

                      be a fairly straightforward amplifier, if some attention is paid to the

                      detail. 2N5109 transistors should work quite well. There are, of course, other

                      choices.



                      5. Observations



                      Many people have wondered how the broadband matching was done in the ALA1530.

                      It is simply done by having an amplifier with a constant input impedance

                      lower than the inductive reactance of the loop at frequencies for which a

                      constant gain is desired.



                      Many people have thought that the amplifier must in some way be exotic. I

                      suggest that it is actually fairly simple, and that this might be the reason for

                      potting it.



                      Later versions of the ALA1530 have an amplifier with better intermodulation

                      performance. They also have a higher quiescent current, and a higher gain.

                      This suggests to me that there are more transistors, probably in a two stage

                      push-pull amplifier.



                      There was a broadband loop available in the UK before the Wellbrook ALA1530

                      was introduced. It was designed by Edward Forster, and sold by his company -

                      Phase Track Ltd, which was based in Reading. His patent - GB2235337 - gives

                      some useful background on broadband loop antennas and their amplifiers.



                      Finally, broadband loop antenas are a compromise solution. At lower

                      frequencies, the radiation resistance is very low, and hence they are very

                      inefiicient. This means that you will not be able to hear signals near the noise floor.

                      Of course, they do appear to offer better noise rejection than an active rod

                      antenna, unless you are very careful (eg see some of Dallas Lankford's recent

                      writings). They are also convenient, and can offer some directionality.



                      HTH and 73



                      John KC0G



                      In a message dated 5/5/07 12:28:19 PM Central Daylight Time,

                      nonlinear@rogers. com writes:

                      > Dear Nigel

                      >

                      > forgot that getting old, I remember that now, I remember seeing the pictures

                      > but was fuzzy on whether for sure bipolars were used

                      >

                      > I believe it was not known from the autopsy whether it was a Norton design

                      > or not

                      > otherwise it is likely a push pull grounded base design for low noise and

                      > wide bandwidth

                      >

                      > what do you think?

                      >

                      > was there a schematic ever published for the Wellbrook

                      >

                      > best

                      > Paul

                      >

                      > ----- Original Message ----

                      > From: "gandalfg8@aol. com" <gandalfg8@aol. com>

                      > To: loopantennas@ yahoogroups. com

                      > Sent: Saturday, May 5, 2007 12:36:40 PM

                      > Subject: Re: [loopantennas] Wellbrook ALA1530

                      >

                      > In a message dated 05/05/2007 17:28:55 GMT Daylight Time,

                      >

                      > nonlinear@rogers. com writes:

                      >

                      > highest gain and lowest noise more likely with jfets

                      > ie more likely in the design than bipolar although not necessarily true if

                      > one considers say the David Norton noiseless design with bipolar

                      > however the Norton design is limited to smaller gains

                      >

                      > ------------ --------- --------- --------- --------- ---------

                      >

                      > "Is more likely" is a bit different to the earlier "must have".

                      > I was just intrigued as to your reasoning, considering that the hardware

                      > content of a dismembered 1530 was discussed here in some detail only a few

                      > weeks

                      > ago and the active devices were obviously bipolar.

                      >

                      > regards

                      > Nigel

                      > GM8PZR

                      >



                      ************ ********* ********* ********

                      See what's free at http://www.aol com.

                      >



                      [Non-text portions of this message have been removed]














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                      [Non-text portions of this message have been removed]
                    • c.e.boyd
                      Hello all: May I remind members of this list that although Mr. Ikin owns the copyright or patent rights, he can not prohibit someone copying his design for
                      Message 10 of 28 , May 10, 2007
                      • 0 Attachment
                        Hello all: May I remind members of this list that although Mr. Ikin owns the
                        copyright or patent rights, he can not prohibit someone copying his design
                        for their own personal use, as long as said individual is not selling these
                        antennae. The speculation of what may constitute the entrails of the "box"
                        is open to discussion, and reverse engineering is not precluded by copyright
                        protections. Only the sale of a clone of Mr. Ikin's design is illegal. Good
                        listening: theboyd
                        ----- Original Message -----
                        From: "Patrick Reynaert" <preynaert@...>
                        To: <loopantennas@yahoogroups.com>
                        Sent: Thursday, May 10, 2007 11:37 PM
                        Subject: Re: [loopantennas] Re: Wellbrook ALA1530


                        > Hi Fraser,
                        >
                        > it looks like my worries about any copyright issues are correct; I just
                        got this email below (or should I say threat) from Andy Ikin himself..
                        >
                        > ===============================
                        >
                        > Dear Mr. Reynaert
                        >
                        > Having just joined the new Loopantennas list. I see that you and some
                        other members are conspiring to breach Wellbrook Communications Copyright
                        of one of its loop antenna designs. I must remind you that Wellbrook
                        Communications owns the design Copyright and all Intellectual Property
                        Rights for its products.
                        >
                        > Yours faithfully
                        >
                        > Andrew H Ikin
                        >
                        > Proprietor
                        > Wellbrook Communications.
                        >
                        >
                        > e-mail: sales@...
                        > andy@...
                        > URL: http://www.wellbrook.uk.com
                        >
                        > Wellbrook Communications
                        > The Farthings
                        > Beulah
                        > Llanwrtyd Wells
                        > Powys
                        > Wales LD5 4YD UK
                        > Tel. 01591 620316 Int.+44 1591 620316
                        >
                        > Manufacturers of Broadband Loop Antennas
                        >
                        > ====================
                        >
                        > Fraser <fraser.castle@...> wrote: I have been following this
                        message thread with great interest.
                        >
                        > Do we know why Patrick is keeping so quiet about the ALA1530 schematic
                        > or even the basic amplifier design (balanced common base bipolar) ?
                        >
                        > Fraser
                      • C. Beijersbergen
                        Patents, as one form of rights protection, are not there to keep things secret. On the contrary, patents are meant to make new knowledge ans solutions public
                        Message 11 of 28 , May 11, 2007
                        • 0 Attachment
                          Patents, as one form of rights protection, are not there to keep things secret. On the contrary, patents are meant to make new knowledge ans solutions public while at the same time protecting the commercial benefits to the owner.

                          One could try to protect one's commercial rights by trying to keep the invention or technology secret. But in that case anyone is free to try to discover the secret.

                          Or one can protect his interests by officially claiming copyrights, patents or otherwise ( it can be different in every country) but than one has to describe formally and publically what is claimed for protection. Others have to have a way to know what they are not allowed to do.
                          The big electronics companies with their large R&D facilities would have no problem with it. In an activity called "competition analysis" the would buy several models of the antenna (through others, so Wellbrook does not realise it happens). These would be tested and measured with the most sophisticated equipment. The antennes would be taken apart, the general build technology would be analysed, the circuitry and the components. Even solidstate devices that have no identification are opened to discover the essential properties, magnet core material will be discovered as well.
                          At the same time they will do a patent analysis. And of course the company has a few experts that will come up with a solution that is slightly different, that circumvents existing rights and very often is slightly better as well.

                          But let's approach this from another side. I think everyone in this group appreciates the Wellbrook products, from own experience or from hearsay. And I can't imagine anyone in this group having the intention of copying these antenna's and taking a marketshare from Wellbrook. Anyone with that intention would not talk about it, but would just do it.
                          The recent discussion is just about our curiosity why the Wellbrook is such a good performer. The group is about designing, building and using loopantenna's. Of course a Wellbrook attracts some attention in a group like that. Taking a commercially available product, opening it and telling others what you see can never be a breach of rights.

                          In my opinion Wellbrook should not wory about the discussions in this group. An we should not wory about exchanging information.

                          regards,

                          Cor Beijersbergen van Henegouwen

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                        • gandalfg8@aol.com
                          In a message dated 11/05/2007 06:39:41 GMT Standard Time, preynaert@yahoo.com writes: Having just joined the new Loopantennas list. I see that you and some
                          Message 12 of 28 , May 11, 2007
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                            In a message dated 11/05/2007 06:39:41 GMT Standard Time,
                            preynaert@... writes:

                            Having just joined the new Loopantennas list. I see that you and some other
                            members are conspiring to breach Wellbrook Communications Copyright of one of
                            its loop antenna designs. I must remind you that Wellbrook Communications
                            owns the design Copyright and all Intellectual Property Rights for its
                            products.



                            ------------------------------
                            Hmmmmmmmmm

                            Neither the list, nor speculation as to the circuitry of the 1530, is new,
                            nor is speculation limited to here, I've seen it elsewhere too, but suggesting
                            there's actually a conspiracy afoot is an interesting consideration.

                            "Too close for comfort" is perhaps an expression that comes to mind:-)

                            I'm not too sure there is such a thing as "design" copyright, in the sense
                            that the word "design" is generally used in the electronics industry, as being
                            the circuit configuration as opposed to a specific appearance.

                            Copyright should offer protection with regards to the appearance of the
                            finished article, and I doubt anyone here would have any problems with that, but
                            the general concept of a broadband loop with a built in amp/matching circuit
                            is well established so one would have to make a literal clone, probably with
                            matching label too, to infringe any "copyright" of the exterior structure.

                            Perhaps it's unfortunate that the expression "Wellbrook clone" has been used
                            here from time to time, when really the intention was only to produce
                            something that gave similar results, but I doubt anyone has ever had any intention
                            of actually making a clone, ie something that could be passed off as the
                            "genuine" article.

                            Copyright can also be applied to an actual PCB layout, although it would
                            need to be the same or at least very similar to be considered to have been
                            copied, but never before have I come across the suggestion that one might hold
                            copyright over a few components mounted on perforated board.
                            If the board layout is documented then perhaps it could be argued there's an
                            infringement if an exact copy is made, otherwise I think it's extremely
                            doubtful that anyone would take the suggestion seriously.

                            So, copyright infringement is unlikely to be an issue unless really making a
                            clone.
                            Copyright on a drawn schematic could certainly apply, if reproduced as per
                            the original, but I doubt copyright could apply to a schematic drawn from
                            circuit tracing a few components.

                            The concept of intellectual property rights is still relatively new, arising
                            mainly I believe from the limitations of existing copyright law when it came
                            to protecting design concepts in computer software.
                            I'm sure most of us still remember the legal cases where "look and feel"
                            arguments took precedence over consideration of function, ie the only protection
                            that existing copyright law gave came very much back to physical appearance
                            only.
                            Again I have doubts as to how one could claim intellectual property rights
                            over a well established concept with at least one lapsed patent putting
                            something presumably very similar into the public domain.

                            I can appreciate the concern, I wouldn't be happy if I perceived income from
                            a high profit margin product as being under threat either, but I'm inclined
                            to feel this heavy handed approach might be counter productive.

                            Despite all the speculation, nobody here, as far as I'm aware anyway, has
                            gone so far as to break apart a working 1530 in order to trace the circuit.
                            If anyone was really determined to do so it wouldn't be all that difficult,
                            as Pat has already demonstrated.
                            I've certainly got no intention of trashing mine, even though it's obvious
                            that replacing the amp would be quite easy once the post mortem was over, but
                            given a physically damaged unit I'd be curious enough do exactly what Pat did
                            and take it apart.

                            I'm still interested in producing my own loop, or loops, similar to the
                            1530, as are many of us, and have always enjoyed the speculation and discussion
                            here, but it's never been my intention to make an exact copy, where's the fun
                            or intellectual challenge in that?
                            If someone did post the actual circuit online, I'm sure I'd build one, out
                            of curiosity as much as anything, but I wouldn't then try and sell it.

                            The only thing that's stopped me pursuing my own ideas, on this and other
                            projects, is repeated house moves and most test gear being in storage for
                            several years now.
                            Seeing as how I should be finally settled, and hopefully up and running some
                            time later this year, it's something I'll be coming back to.

                            I don't suppose I'd be selling anything as a result but if I did it would be
                            properly made, and I wouldn't take kindly to the suggestion that my having
                            seen an out of focus photo of a trashed 1530 with it's kitchen sink style of
                            construction meant that I was somehow breaching any copyright or intellectual
                            property rights.

                            regards

                            Nigel
                            GM8PZR








                            [Non-text portions of this message have been removed]
                          • Fraser
                            An interesting turn of events ! Thank you Patrick for the comment on my earlier question... I was wondering if you had been contacted and now see that I was
                            Message 13 of 28 , May 11, 2007
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                              An interesting turn of events !

                              Thank you Patrick for the comment on my earlier question... I was
                              wondering if you had been 'contacted' and now see that I was correct
                              in my suspicion. I fully understand your reluctance to breach any
                              copyright or IPR that may be in place.

                              As a contrast to Andy Irkins comments I must say that I have been very
                              pleasantly surprised by many of my RF equipment suppliers when it
                              comes to schematics. AOR has provided me with the Schematics of their
                              antennas on the condition that I do not use the information for
                              commercial gain. Sony have also made their schematics for the AN-LP1
                              loop freely available for non commercial use. ICOM have ALWAYS agreed
                              to supply me with schematics and service manuals.

                              I can understand Andy Irkins concern however. From what has been said,
                              Wellbrook is a very small business and we are on the edge of revealing
                              his ALA1530's 'secret'. With the required information, SWL's will be
                              able to build their own ALA1530 clone and save themselves £160. The
                              question has to be.... is this piracy or is it just what Amateur Radio
                              enthusiasts and SWL's do for entertainment and learning ?

                              Fraser
                            • Vince Werber
                              I am sure this antenna is quite nice but I know from long experience that a true resonant loop will out play and perform most any of these commercial
                              Message 14 of 28 , May 11, 2007
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                                I am sure this antenna is quite nice but I know from long experience that
                                a true resonant loop will out play and perform most any of these
                                commercial designs... Why? Because with the commercial designs a great
                                many of compromises are being made... most of us have specific needs and
                                our designs will reflect that fact.

                                Loop antennas have a long history and let's be truthful here... There is
                                NO true innovation with these newer designs... Most are derivitive at the
                                very least...

                                Most everyone on this list can do better by using the simple designs from
                                history, making sure they are resonate, making sure they are showing the
                                correct value of load and have a decent Q...

                                I wouldn't waste my time trying to reverse engineering any design because
                                I honestly know I can do much better for my specific needs...

                                end of rant...

                                vince
                                p.s. I don't use 'amplified' designs at all because along with the signal
                                these designs amplify the noise also...


                                On Fri, 11 May 2007, gandalfg8@... wrote:

                                >
                                > In a message dated 11/05/2007 06:39:41 GMT Standard Time,
                                > preynaert@... writes:
                                >
                                > Having just joined the new Loopantennas list. I see that you and some other
                                > members are conspiring to breach Wellbrook Communications Copyright of one of
                                > its loop antenna designs. I must remind you that Wellbrook Communications
                                > owns the design Copyright and all Intellectual Property Rights for its
                                > products.
                                >
                                >
                                >
                              • Paul Birke
                                thanks for letting us know Partrick agree with your concerns likely the low non-inductive resistance across the loop to obtain the wide bandwidth is what some
                                Message 15 of 28 , May 11, 2007
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                                  thanks for letting us know Partrick

                                  agree with your concerns

                                  likely the low non-inductive resistance across the loop
                                  to obtain the wide bandwidth is what some of us were
                                  missing so as to give reason for its superior performance
                                  besides of course of the low noise vhf bipolar transistors

                                  best wishes

                                  Paul V Birke PEng
                                  Guelph ON Canada


                                  [Non-text portions of this message have been removed]
                                • Steve
                                  ... said, ... revealing ... Radio ... Ahem. From http://www.uspto.gov the US Govt s Patent, Trademark, and Copyright website: The copyright protects the form
                                  Message 16 of 28 , May 11, 2007
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                                    --- In loopantennas@yahoogroups.com, "Fraser" <fraser.castle@...> wrote:
                                    ....
                                    > I can understand Andy Irkins concern however. From what has been
                                    said,
                                    > Wellbrook is a very small business and we are on the edge of
                                    revealing
                                    > his ALA1530's 'secret'. With the required information, SWL's will be
                                    > able to build their own ALA1530 clone and save themselves £160. The
                                    > question has to be.... is this piracy or is it just what Amateur
                                    Radio
                                    > enthusiasts and SWL's do for entertainment and learning ?

                                    Ahem. From http://www.uspto.gov the US Govt's Patent, Trademark, and
                                    Copyright website:

                                    "The copyright protects the form of expression rather than the subject
                                    matter of the writing. For example, a description of a machine could be
                                    copyrighted, but this would only prevent others from copying the
                                    description; it would not prevent others from writing a description of
                                    their own or from making and using the machine."

                                    So a Patent provides protection for the design for a physical machine
                                    such as a loop antenna. A copyright (as others have pointed out) only
                                    protects the exact appearance of that completed machine, and so prevent
                                    a competitor from producing a counterfeit. And it must be substantially
                                    unique in appearance to warrant protection by copyright, or only minor
                                    changes allow similar looking machines from appearing (as others have
                                    also pointed out).

                                    Steve Greenfield
                                  • Jay Heyl
                                    ... I respectfully suggest you should try one of the Wellbrook antennas before expressing an opinion on how some other antenna would stack up against it. --
                                    Message 17 of 28 , May 11, 2007
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                                      On 5/11/07, Vince Werber <ka1iic@...> wrote:

                                      > Most everyone on this list can do better by using the simple designs from
                                      > history, making sure they are resonate, making sure they are showing the
                                      > correct value of load and have a decent Q...

                                      I respectfully suggest you should try one of the Wellbrook antennas
                                      before expressing an opinion on how some other antenna would stack up
                                      against it.

                                      -- Jay
                                    • Laurence Taylor
                                      ... and some other members are conspiring to breach Wellbrook Communications Copyright of one of its loop antenna designs. I must remind you that Wellbrook
                                      Message 18 of 28 , May 12, 2007
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                                        > Having just joined the new Loopantennas list. I see that you
                                        and some other members are conspiring to breach Wellbrook
                                        Communications Copyright of one of its loop antenna
                                        designs. I must remind you that Wellbrook Communications
                                        owns the design Copyright and all Intellectual Property
                                        Rights for its products.
                                        >
                                        > Yours faithfully
                                        >
                                        > Andrew H Ikin
                                        >
                                        > Proprietor
                                        > Wellbrook Communications.

                                        Well, I know whose loop I won't be buying then, if that's the way
                                        he joins a thread! What an attitude to take to people who might
                                        otherwise be supportive of his product.

                                        It's of no consequence; there's plenty of other designs, and I
                                        doubt if his effort is significantly different; there's only a
                                        certain number of ways you can make something!

                                        rgds
                                        LAurence

                                        ... "Yield to temptation, it may not pass your way again." - L. Long
                                        ~~~ Tag-O-Matic V.13F
                                      • Len Warner
                                        ... Allegation of involvement in a conspiracy is not what I would call civil - more like civil-actionable . How fortunate for Mr Ikin that he put his
                                        Message 19 of 28 , May 12, 2007
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                                          At 14:03 07/05/12, Digest Number 813 wrote:
                                          > Posted by: "n2chi" davidgriffin@... n2chi
                                          > Date: Fri May 11, 2007 3:56 pm ((PDT))
                                          >
                                          >Andy's note ... his note seemed perfectly civil.

                                          Allegation of involvement in a conspiracy is not
                                          what I would call "civil" - more like "civil-actionable".

                                          How fortunate for Mr Ikin that he put his allegation
                                          into a private email and not publicly to the group!

                                          (And would most of you learn to trim so that your
                                          comment is not dwarfed by your huge quote?)


                                          Regards, LenW
                                          --
                                          If you are sending a reply to a message... be sure you summarize the
                                          original at the top of the message, or include just enough text of
                                          the original to give a context. This will make sure readers under-
                                          stand when they start to read your response.... Giving context helps
                                          everyone. But do not include the entire original! (rfc1855)
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