Loading ...
Sorry, an error occurred while loading the content.

Chokes

Expand Messages
  • Shawn E. Korgan
    Greetings, There were many S1-S2 whistlers occurring here in Colorado on Monday night (at least a dozen a minute) during tests upon my VLF receiver. The
    Message 1 of 22 , Jul 1, 2003
    • 0 Attachment
      Greetings,

      There were many S1-S2 whistlers occurring here in Colorado on Monday
      night (at least a dozen a minute) during tests upon my VLF receiver. The
      whistlers were very diffuse (hissy) and several had many echoes (up to a
      dozen on several instances).

      As a quick follow up to my previous experiment utilizing series
      inductance in-line with the antenna of VLF receivers to eliminate out of
      band interference, I ordered four additional chokes to test. The
      following are my final analysis. Any choke which is 5H (5 henries of
      inductance) or greater will create a distorted sounding frequency
      response in most VLF receivers due to an overemphasis of frequency
      response in a narrow band of frequencies within the band of interest. A
      3.5H choke rolls off the frequencies above about 9 KHz. The only problem
      is that this choke still produced a slightly overemphasized frequency
      response in the VLF frequencies of interest and made the reception sound
      somewhat distorted. A 2H choke was a good selection and appeared to roll
      off frequencies above about 11 KHz. There was still just a slight touch
      of overemphasis noticeable upon certain VLF frequencies of interest. A
      2H choke would be the highest value I would attempt to use to eliminate
      LF band interference (such as from LORAN [100 KHz], WWVB [60 KHz], etc.)
      A 1.5H choke rolled off frequencies above about 14 KHz or so and had
      almost no effect upon the VLF reception in my receiver.

      There was no LORAN or WWVB interference present during these tests so I
      was unable to test the chokes against live LF band interference on my VLF
      receiver. Most often, I receive LORAN interference during the early
      morning hours just before sunrise and occasionally during the nighttime
      hours but never during the day. Once I receive the 1 henry choke in the
      mail, I will test it out against live interference on my VLF receiver
      (next time it is noticed) and will pass along any results on how
      effective the choke is at eliminating LORAN interference.

      After all is said and done, I plan to order and keep on hand a 1 henry
      choke from Digi-Key. This value (1 henry of inductance) appears to be
      the best selection to eliminate upper band interference from VLF
      receivers without degrading or distorting the VLF reception in VLF
      receivers. The catalog number is 158T with a price of $17.66. (Note.- A
      $5 handling charge is added to the order if the subtotal is less than
      $25.) www.digikey.com

      I thought I would pass this along just in case someone is interested in
      trying something down this line to eliminate upper band interference from
      their own VLF receiver.

      Shawn Korgan
      INSPIRE Team I-1

      [Non-text portions of this message have been removed]
    • Leonard J. Kerry
      Shawn and Group. Just a general comment for everyone s consideration on the use of inductors in the antenna circuits of VLF receivers. For an inductor to form
      Message 2 of 22 , Jul 1, 2003
      • 0 Attachment
        Shawn and Group.

        Just a general comment for everyone's consideration on the use of inductors in the antenna circuits of VLF receivers. For an inductor to form part of a low pass filter, it has to work in conjunction with a load consisting of either a pure resistance or in shunt with a capacitance. As can be seen from the discussions that take place within this group, there is no standard configuration for the antenna port impedance of a VLF receiver - some have very high resistance with every attempt made to minimize shunt capacitance, others have a much lower input resistance shunted with a deliberate capacitance. There are many variations in-between. The type of antenna to be used also impacts the choice of antenna port design along with personal design goals!

        Thus, an inductor that may appear to provide a filtering benefit in one receiver may actually be entirely unsuitable for use in a different receiver.

        For those who wish to experiment along the same lines as Shawn, remember to do your own experimentation and analysis to ensure that you don't degrade the existing level of performance provided by your receiver!

        Len

        -----Original Message-----
        From: Shawn E. Korgan [mailto:ShawnKorgan@...]
        Sent: Wednesday, 2 July 2003 5:43 AM
        To: VLF_Group@yahoogroups.com
        Subject: [VLF_Group] Chokes


        Greetings,

        There were many S1-S2 whistlers occurring here in Colorado on Monday
        night (at least a dozen a minute) during tests upon my VLF receiver. The
        whistlers were very diffuse (hissy) and several had many echoes (up to a
        dozen on several instances).

        As a quick follow up to my previous experiment utilizing series
        inductance in-line with the antenna of VLF receivers to eliminate out of
        band interference, I ordered four additional chokes to test. The
        following are my final analysis. Any choke which is 5H (5 henries of
        inductance) or greater will create a distorted sounding frequency
        response in most VLF receivers due to an overemphasis of frequency
        response in a narrow band of frequencies within the band of interest. A
        3.5H choke rolls off the frequencies above about 9 KHz. The only problem
        is that this choke still produced a slightly overemphasized frequency
        response in the VLF frequencies of interest and made the reception sound
        somewhat distorted. A 2H choke was a good selection and appeared to roll
        off frequencies above about 11 KHz. There was still just a slight touch
        of overemphasis noticeable upon certain VLF frequencies of interest. A
        2H choke would be the highest value I would attempt to use to eliminate
        LF band interference (such as from LORAN [100 KHz], WWVB [60 KHz], etc.)
        A 1.5H choke rolled off frequencies above about 14 KHz or so and had
        almost no effect upon the VLF reception in my receiver.

        There was no LORAN or WWVB interference present during these tests so I
        was unable to test the chokes against live LF band interference on my VLF
        receiver. Most often, I receive LORAN interference during the early
        morning hours just before sunrise and occasionally during the nighttime
        hours but never during the day. Once I receive the 1 henry choke in the
        mail, I will test it out against live interference on my VLF receiver
        (next time it is noticed) and will pass along any results on how
        effective the choke is at eliminating LORAN interference.

        After all is said and done, I plan to order and keep on hand a 1 henry
        choke from Digi-Key. This value (1 henry of inductance) appears to be
        the best selection to eliminate upper band interference from VLF
        receivers without degrading or distorting the VLF reception in VLF
        receivers. The catalog number is 158T with a price of $17.66. (Note.- A
        $5 handling charge is added to the order if the subtotal is less than
        $25.) www.digikey.com

        I thought I would pass this along just in case someone is interested in
        trying something down this line to eliminate upper band interference from
        their own VLF receiver.

        Shawn Korgan
        INSPIRE Team I-1

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



        Post message: VLF_Group@yahoogroups.com
        Subscribe: VLF_Group-subscribe@yahoogroups.com
        Unsubscribe: VLF_Group-unsubscribe@yahoogroups.com
        List owner: VLF_Group-owner@yahoogroups.com
        VLF group web page (archive and information): http://groups.yahoo.com/group/VLF_Group/

        Members of the VLF discussion group may request the option of receiving just one e-mail per day (or no e-mail). This e-mail will be sent at the end of each day and will include all of the days' comments. Simply send an e-mail to the list owner (VLF_Group-owner@yahoogroups.com) requesting digest mode (or no e-mail).

        Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
      • vlf_ddd
        Shawn, I wonder if the low pass effect you are getting with those iron core inductors are from the effects of the inductance with your input circuit, or from
        Message 3 of 22 , Jul 1, 2003
        • 0 Attachment
          Shawn,
          I wonder if the low pass effect you are getting with those iron core
          inductors are from the effects of the inductance with your input
          circuit, or from the properties of the chokes themselves.

          The iron cores are going to be very lossy at higher frequencies,
          likely rolling off somewhere in the 10kHz range regardless of the
          circuit you put them in. If the choke is acting as a low pass filter
          by itself, then any similar choke in series with the antenna and a
          high input impedance should produce similar results for a wide range
          of input circuits.

          One way to test if the choke is acting like an ideal (but lossy)
          inductor or a low pass filter element is to put two in parallel.

          Lets assume that your 3.5 H choke is a 157Q and your 1.5 H choke is a
          158S. If so, the two in parallel should look like a 1.05 H choke with
          a DC resistance 38.2 ohms. This is very close to the impedance of the
          158T (1H at 40 ohms DC).

          If the chokes are still acting like inductors, then you should see the
          roll off frequency go up (likely around 17/18 kHz). If the choke are
          providing the attenuation through internal losses, then the two in
          parallel would act like two low pass filters in parallel, i.e. you
          would still start to see attenuation at the lower frequency (9 kHz for
          the 3.5 H), then the attenuation rate would double at the higher
          frequency (14 kHz for the 1.5 H).

          Would be interested to know what happens if you try to do this.
        • Shawn E. Korgan
          Greetings, ... The low pass effect appears to be the property of the chokes. I tried choke values ranging from 150 henries to values within the mH range and
          Message 4 of 22 , Jul 2, 2003
          • 0 Attachment
            Greetings,

            RE:

            > I wonder if the low pass effect you are getting with those iron
            > core inductors are from the effects of the inductance with
            > your input circuit, or from the properties of the chokes
            > themselves.

            The low pass effect appears to be the property of the chokes. I tried
            choke values ranging from 150 henries to values within the mH range and
            the results are consistent. The cutoff frequency changes proportionately
            with the amount of inductance used. Results will vary slightly with
            different VLF receivers due to different internal setups (shunting
            capacitance, amount of loading, etc.)

            > The iron cores are going to be very lossy at higher frequencies,
            > likely rolling off somewhere in the 10kHz range regardless of the
            > circuit you put them in.

            The frequencies most of us are concerned with further eliminating are the
            ones which are immediately above the VLF band (especially 24-100 KHz).

            Currently, I use two 150 mH chokes both before and after my front end FET
            in series with the signal in my E-field receiver. These were in place at
            the time I tested the large chokes. These little guys (the 150mH chokes)
            are extremely important to eliminate out of band interference from
            shortwave radio stations, AM radio stations and lower frequency LF
            stations such as LORAN and WWVB in my receiver.

            As a very important side note to this subject and as to the reason why I
            use chokes in my receiver in the first place, I have chosen not to use
            the resistive / capacitive (RC) low pass filters so many VLF
            experimenters use on the front ends of their VLF receivers due to the
            simple fact that series resistance can drastically destroy the signal to
            noise ratio! As little as several hundred ohms of series resistance
            begins to deteriorate the VLF signal in my receiver adding white noise to
            the signal (when using two 8' antennas for reception). The RC low pass
            filter setups are terrific for eliminating out of band interference on
            VLF receivers but they also appear to be terrific for making VLF
            receivers typically around 10 dB less sensitive also! (Again, results
            will vary upon the particular receiver setup). To get around this, I
            have pulled out the RC filter and now use series inductance instead.
            This removes the noise and attenuation created by the RC filter and
            replaces it with basically noiseless inductors with no attenuation of the
            VLF signal noticeable. This, more than anything else, is what makes my
            SK-1 receiver typically 10 dB greater in sensitivity over similar VLF
            receivers.

            Most VLF receiver schematics on the web show anywhere from 10K to 500K of
            series resistance for the RC filter. By shorting any resistors that are
            in series with the incoming VLF signal each member should be able to hear
            for themselves just how much of an improvement can be obtained in their
            signal to noise ratio (sensitivity) by simply changing from an RC low
            pass filter to series inductance! Just a thought...

            > If the choke is acting as a low pass filter by itself, then any
            > similar choke in series with the antenna and a high input
            > impedance should produce similar results for a wide range
            > of input circuits.

            This does indeed appear to be the case with different values of
            inductance corresponding directly to the frequencies which are rolled
            off.

            > One way to test if the choke is acting like an ideal (but lossy)
            > inductor or a low pass filter element is to put two in parallel.
            > Lets assume that your 3.5 H choke is a 157Q and your 1.5 H
            > choke is a 158S. If so, the two in parallel should look like a
            > 1.05 H choke with a DC resistance 38.2 ohms. This is very
            > close to the impedance of the 158T (1H at 40 ohms DC).

            > If the chokes are still acting like inductors, then you should see
            > the roll off frequency go up (likely around 17/18 kHz). If the
            > choke are providing the attenuation through internal losses,
            > then the two in parallel would act like two low pass filters in
            > parallel, i.e. you would still start to see attenuation at the lower
            > frequency (9 kHz for the 3.5 H), then the attenuation rate
            > would double at the higher frequency (14 kHz for the 1.5 H).

            The cutoff frequency does indeed rise when two chokes are placed in
            parallel. Also, it's important to note that the signal to noise ratio is
            unaffected by the addition of the 1.5 henry choke rated at close to just
            50 ohms.

            I hope this sparks a few tests in everyone's mind!

            All the best :-)

            Shawn Korgan
            INSPIRE Team I-1
          • Richard Gagnon
            Hi Shawn Could you post a schematic of your SK-1 receiver using the chokes? This option sounds interseting. Thank you. Richard Gagnon
            Message 5 of 22 , Jul 2, 2003
            • 0 Attachment
              Hi Shawn

              Could you post a schematic of your SK-1 receiver using the chokes? This option
              sounds interseting. Thank you.

              Richard Gagnon

              __________________________________
              Do you Yahoo!?
              SBC Yahoo! DSL - Now only $29.95 per month!
              http://sbc.yahoo.com
            • Shawn E. Korgan
              Hi Richard and group, I do not have a ready schematic that I can post to the group at the present time. It s only on paper and is a design that is still in
              Message 6 of 22 , Jul 2, 2003
              • 0 Attachment
                Hi Richard and group,

                I do not have a ready schematic that I can post to the group at the
                present time. It's only on paper and is a design that is still in
                progress. Currently, I send the incoming signal through a 150 mH choke
                (available from www.mouser.com) which ties to the gate of the FET. The
                signal then travels through a second 150 mH choke on the output side of
                the FET as it heads toward the input of the second stage (an NPN/bipolar
                transistor). I use no shunting capacitance and no series resistance
                (other than what is contained in the 150mH chokes - approx. 160 ohms a
                piece) before the FET transistor, and I use at least 44M of gate bias
                resistance (resistance between the gate of the FET and the ground).

                This will make for a hot receiver!

                Shawn


                On Wed, 2 Jul 2003 11:30:45 -0700 (PDT) Richard Gagnon
                <richg_1998@...> writes:
                > Hi Shawn
                >
                > Could you post a schematic of your SK-1 receiver using the chokes?
                > This option
                > sounds interseting. Thank you.
                >
                > Richard Gagnon
              • vlf_ddd
                ... Just curious, why do you use two antennas instead of one taller one? Also... How are they spaced / oriented w/ respect to each other and your receive
                Message 7 of 22 , Jul 2, 2003
                • 0 Attachment
                  > ... (when using two 8' antennas for reception). ...

                  Just curious, why do you use two antennas instead of one taller one?

                  Also...

                  How are they spaced / oriented w/ respect to each other and your
                  receive equipment?

                  Any ground plane?

                  What do you use as a Tx line?

                  How do you combine them?

                  Thanks
                • Shawn E. Korgan
                  Greetings group, ... One very tall antenna would work better than several shorter antennas. The only problem I have encountered is trying to get a tall antenna
                  Message 8 of 22 , Jul 3, 2003
                  • 0 Attachment
                    Greetings group,

                    RE:

                    > Just curious, why do you use two antennas instead
                    > of one taller one?

                    One very tall antenna would work better than several shorter antennas.
                    The only problem I have encountered is trying to get a tall antenna to
                    stand upright when it gets much over ten feet in height. The perfect
                    antenna would be around twenty or thirty feet in height. I know this
                    after doing several experiments with an eight foot helium filled weather
                    balloon several years ago. Fifty feet was overkill and eight feet is way
                    too short. Somewhere around twenty to thirty feet appeared to provide
                    the most usable signal. Thirty feet is the height recommended in the
                    book, "Whistlers and Related Ionospheric Phenomena" by Dr. Helliwell.

                    > Also... How are they spaced / oriented w/ respect to
                    > each other and your receive equipment?

                    Currently, I have two eight foot antennas mounted permanently on the rear
                    bumper of my car (on opposite ends of the bumper). I have the option of
                    adding two additional eight foot antennas to the front bumper of my car
                    when extra signal strength is needed such as during very quiet VLF
                    conditions.

                    > Any ground plane?

                    I have always simply grounded my receiver to the car for a ground plane!
                    There is no need for ground stakes or ground rods (they do not help) when
                    I use the eight foot antennas on the bumper of my car.

                    For longwire antenna users, I have found that a ground rod or
                    counterpoise is important. A counterpoise is simply a long piece of wire
                    laid along the ground (usually in the opposite direction of the VLF
                    antenna layout) that ties to the receiver's ground.

                    > What do you use as a Tx line?

                    Currently, I use TV coax cable! This works very well on my receiver!
                    The VLF signal actually sounds cleaner with the ground of the coax
                    connected than with it disconnected.

                    > How do you combine them?

                    I have a separate front-end box for my receiver that has four 'F' type
                    antenna connectors on it for antenna hookup purposes. Internally, these
                    connectors are simply all soldered one to another. This front-end box
                    contains such things as the first 150mH choke, the series capacitance (to
                    protect the gate of the FET) and the gate bias resistor. All the other
                    parts are in the actual VLF receiver which also hooks to the front-end
                    box via a short coax cable. The main purpose I use a front-end box is to
                    keep any stray radio interference out of my receiver. I also use very
                    thin coax cable within my receiver to carry the incoming VLF signal from
                    the connector on the VLF receiver to the circuit board. One cannot be
                    too careful to prevent the incoming signal from leaking into a later
                    stage (bypassing all earlier filtering) in the receiver and thereby
                    creating radio interference.

                    > Thanks

                    It's my pleasure.

                    Shawn Korgan
                    INSPIRE Team I-1
                  • WarmSpgs@aol.com
                    ... I am intrigued by this. White noise from several hundred ohms, in a high impedance circuit? Could we see a schematic of your receiver s front end?
                    Message 9 of 22 , Jul 3, 2003
                    • 0 Attachment
                      >As little as several hundred ohms of series resistance
                      >begins to deteriorate the VLF signal in my receiver
                      >adding white noise to
                      >the signal (when using two 8' antennas for reception).

                      I am intrigued by this. White noise from several hundred ohms, in a high
                      impedance circuit? Could we see a schematic of your receiver's front end?

                      Thanks.

                      John
                    • mike l dormann
                      you are correct in keeping the series resistance low in the series lead of your first transistor in your receiver, the most sensitive rx i ever had was back in
                      Message 10 of 22 , Jul 3, 2003
                      • 0 Attachment
                        you are correct in keeping the series resistance low in the series lead
                        of your first transistor in your receiver, the most sensitive rx i ever
                        had was back in the omega days, made a 5000 foot dipole on the ground (up
                        8 feet or so so i did not tangle with it), fed a high hz to low z
                        transformer and followed with a 4 inductor low pass filter with
                        transmission zeros at the two strongest omega frequencies, now we are
                        sitting with a 50-100 ohm output impedance, and used grounded gate
                        technology as a first stage.....
                      • Shawn E. Korgan
                        Greetings, This is true. As small as several hundred ohms of series resistance with my antenna begins to just very slightly add white noise (almost
                        Message 11 of 22 , Jul 3, 2003
                        • 0 Attachment
                          Greetings,

                          This is true. As small as several hundred ohms of series resistance with
                          my antenna begins to just very slightly add white noise (almost
                          unnoticeable) to the signal in my receiver. Looking at an audio test I
                          performed several years ago, a series resistance of 100 K adds close to
                          10 dB of white noise to the VLF signal! That's a large amount of
                          additional noise. Many VLF receivers use even greater than 100 K of
                          resistance in line with their incoming VLF signal. This creates a lot of
                          noise and really covers up a lot of fascinating VLF activity that would
                          be captured otherwise.

                          There is not much to my front end. It is probably the simplest a person
                          has ever imagined. The incoming signal travels through a 150 mH choke
                          and then through a 0.01 uF capacitor and then feeds directly into the
                          gate of an ordinary FET transistor. The gate bias resistor (between the
                          gate and ground) is 44 M ohms of resistance. Any less resistance than
                          this also begins to add white noise to the VLF signal in my receiver.
                          More than 44 M of gate bias resistance is preferable but then the FET can
                          go nonlinear when the wind blows against the antennas and creates a
                          slight charge upon them.

                          The limiting factor for my receiver currently is not internal noise but
                          rather the natural noise floor that is always present in the VLF band.
                          At times, this noise floor mysteriously plummets. Could solar flares be
                          the cause of this? It is when the natural noise floor plummets
                          (sometimes within minutes) that power lines appear to suddenly be louder
                          than usual and also when I begin to receive faint interference from LORAN
                          and occasionally from WWVB. Whatever causes the natural VLF noise floor
                          to plummet may also intensify reflections of various VLF frequencies off
                          the D-layer? When the noise floor plummets VLF activity often becomes
                          very fascinating to listen to with what appears at first to be louder
                          than usual whistlers and other strange sounding activity.

                          Now, all I need to do is try the 1 henry choke next time interference
                          occurs to see if it solves it!

                          Just a few thoughts.

                          Shawn Korgan
                          INSPIRE Team I-1


                          On Thu, 3 Jul 2003 12:46:04 EDT WarmSpgs@... writes:
                          > >As little as several hundred ohms of series resistance
                          > >begins to deteriorate the VLF signal in my receiver
                          > >adding white noise to
                          > >the signal (when using two 8' antennas for reception).
                          >
                          > I am intrigued by this. White noise from several hundred ohms, in a
                          > high
                          > impedance circuit? Could we see a schematic of your receiver's
                          > front end?
                          >
                          > Thanks.
                          >
                          > John
                        • mdennisond@aol.com
                          Hi Shawn & all, Shawn do you have a spectogram of the noisefloor when it s strong & when it s not. Thanks, Mark. [Non-text portions of this message have been
                          Message 12 of 22 , Jul 3, 2003
                          • 0 Attachment
                            Hi Shawn & all,
                            Shawn do you have a spectogram of the noisefloor when it's strong & when it's
                            not.

                            Thanks,
                            Mark.


                            [Non-text portions of this message have been removed]
                          Your message has been successfully submitted and would be delivered to recipients shortly.