Re: [loopantennas] Re: Tranmitting Loop for 6m & 10m

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• That would work and it would fit the capacitor you have but you could go larger. Your numbers are off in a couple of places. The conversion from English to
Message 1 of 21 , Jul 31 11:42 PM
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That would work and it would fit the capacitor you have but you could go
larger. Your numbers are off in a couple of places. The conversion from
English to metric are wrong it is not a division by 4 but 3.3. Also, you
can not assume the velocity to be .66. It think that is way too much for
this exercise.

de_9w2dtr wrote:
> --- In loopantennas@yahoogroups.com, W2XJ <w2xj@...> wrote:
>
>>
>>I agree that the loop is too large. The circumference needs to be less
>>than 1/4 wave. With 47 cm diameter, you are right at 1/4 wave length
>>before you consider velocity and loading. If you go to a diameter
>>slightly less than 40 CM, it should tune on 6 M and be about 60 %
>>efficient on 10 M if you use around 1 inch (25mm) tubing. Also, your
>>capacitor is to large. You need about 26 pf for 10 m and half that
>
> on 6.
>
>> With a capacitor 10 times too large, tuning at the bottom of the
>
> range
>
>>could be difficult. What kind of match are you using - gamma match or
>>loop coupling? How much power do you plan to use?
>>
>
>
> I am using a Farady Loop for coupling the RF feed.
> Is there any usage of Balun and tuner should be considered?
>
>>From my calculation, with the velocity factor of 0.66, for 54Mhz
> frequency. The loop diameter for 1/4w will be about 29cm. Is this
> correct? I use this formula, 300/54=5.55, 5.55/4=1.388,
> 1.388*0.66=0.916, 0.916/pi=29.1cm.
>
> I am using a 12mm microwave coax cable for the loop.
>
>
• ... You do not say what the winding pitch is: my bet is that your loop is close wound, in which case the loop s self- resonance will be at around 2Mhz. (It
Message 2 of 21 , Jul 31 11:55 PM
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At 7:40 am ((PDT)) Mon Jul 30, 2007, in Digest 881, Richards wrote:

>[snip] For my experiment, I tuned weak and moderate signals
>in the 31 m short wave band (around 9.4 MHz).
>
>What seemed to work as well as anything, was a mere 16 seat of wire
>looped twice around a 2 foot by 2 foot square PVC pipe frame I built for
>another purpose. Using coax cable feed line, it did not seem to matter
>whether I connected just one end of the wire loop, or both ends - one
>end to the coax cable center conductor, and the other to the shield.
>I don't know why it did not matter how I connected it, but it
>seemed to work the same either way.

You do not say what the winding pitch is: my bet is that
your loop is close wound, in which case the loop's self-
resonance will be at around 2Mhz. (It depends somewhat
on wire diameter, which you also didn't care to tell us.)

You would benefit from RJELOOP3.EXE by Reg Edwards.

This is designed for square receiving loops and will tell you
the inductance, approximate self-resonance frequency,
capacitor for resonance (if used) and other interesting
parameters.

By using RJELOOP3 you will discover that you need to
increase the winding pitch to 2 wire diameters or more
in order to raise the self-resonance above your frequency
of interest.

If you are planning to tune the loop I would suggest a bigger
spacing, since self-capacitance is worse for Q than a good-
quality external C and will also limit the tuning range attainable.

>[snip]
>I wonder whether tuning capacitor would help adjust the wire to various
>frequencies above

Not practical: the loop is already capacitive above its
parallel resonance.

>or below its resonant frequency?

Yes, but first you need to raise its self-resonance above

>I wonder whether I could locate the tuning capacitor in
>the shack, rather than out at the loop in the backyard?

Yes, if you don't mind adding the resistance and capacitance
of your feeder to the loop resonant circuit (which you should).

>I am, based on the discussion here, presuming that my
>16 foot long wire in a

How does

>figure-8 double loop

relate to

>(i.e. going twice around my 2 feet per side pvc frame)

?

Or are you trying to tell us at this late stage in the discussion
that you wound it with figure-8 zip cord?

>is approximately 1/10 wavelength for the 31 m (9.5 MHz)

300m/9.5Mhz = 104ft approx.; 16ft = 0.154 wavelength;
a >50% error over 1/10 wavelength but, since you have
coiled it, you have brought the low-current ends back to
overlap the maximum-current centre, so the spacial
distribution of current will be more uniform than a single
turn of this wire length would have been and I'm guessing
that means it will give you good "small loop" performance.

>I also presume that I would have to select a different
>length of wire, perhaps, or a different band in the spectrum. Or is
>this mistaken, would any short loop work? Would any short length work,
>but with a tuner?

Any loop of wire below its self-resonant frequency behaves
just as you should expect a loop of wire to behave: it has an
area which determines how it interacts with the spatial RF field
and an inductance and capacitance which determines how
you can couple it to the rest of your circuit.

When the length is greater the spatial arrangement and
possible self-resonant modes take over, and you will need
either experiment or an antenna-modelling package to
discover what its impedance and radiation pattern are,
which is one reason for sticking with published designs
so you can benefit from someone else's experience.

Regards, LenW
• ... Only if it is to be a small receiving loop: it is marginal as a small transmitting loop; and there is no restriction on (approx) multiple
Message 3 of 21 , Aug 1, 2007
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At 1:21 pm ((PDT)) Tue Jul 31, 2007, in Digest 882, W2XJ wrote:

>I agree that the loop is too large. The circumference needs to be less
>than 1/4 wave.

Only if it is to be a "small" receiving loop: it is marginal as
a "small" transmitting loop; and there is no restriction on
(approx) multiple half-wavelengths being used in a large loop.

For example, see "The Loop Skywire" and the following
"7-MHz Loop" in ARRL Antenna Book chapter 5, both of
which have multiple modes above their fundamental (and
the Skywire as a top-hat loaded vertical too).

>With 47 cm diameter, you are right at 1/4 wave length

Both MLOOP31 and RJELOOP1 say it should tune 50MHz
and work with good efficiency with a 25mm conductor...

>If you go to a diameter
>slightly less than 40 CM, it should tune on 6 M and be about 60 %
>efficient on 10 M if you use around 1 inch (25mm) tubing. Also, your
>capacitor is to large. You need about 26 pf for 10 m and half that on 6.

... with about 8pF or 9pF respectively, though we know
this value must be marginal for Dexter's variable capacitor.

(RJELOOP1 says only 4.4pF with a 1mm conductor.)

For 10MHz, RJELOOP1 predicts 29.3pF.

> With a capacitor 10 times too large, tuning at the bottom of the range
>could be difficult. What kind of match are you using - gamma match or
>loop coupling? How much power do you plan to use?

There are many specific details Dexter hasn't given us,
(though I see there are some later in this Digest)
probably because he doesn't understand them himself yet
or have enough information to reach a decision.

I suggest it is time for Dexter to do his own legwork and at least
play with RJELOOP1 (or MLOOP31) until he gets a feel for the
numbers and preferably also read chapter 5 of ARRL Antenna Book
to get a handle on the theory and some specific designs.

And would contributors please _not_ quote most of the history
of this thread into their messages - especially top-posted into
reverse or higgledy-piggledy order. I can't easily follow much
of the quote in your message and I see I wrote most of it!

Quotes should give _context_ - and they need to be come before
the reply to do that - not _history_ - we have an Archive for that.

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-
everyone. But do not include the entire original! (rfc1855)
• ... Faraday: Michael Faraday, an English natural philosopher http://en.wikipedia.org/wiki/Michael_Faraday ... A balun provides a BAlanced to UNbalanced (or an
Message 4 of 21 , Aug 1, 2007
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At 9:05 pm ((PDT)) Tue Jul 31, 2007, in Digest 882, de_9w2dtr wrote:

>--- In loopantennas@yahoogroups.com, W2XJ <w2xj@...> wrote:
> >
> >
> > I agree that the loop is too large. The circumference needs to be less
> > than 1/4 wave. With 47 cm diameter, you are right at 1/4 wave length
> > before you consider velocity and loading. If you go to a diameter
> > slightly less than 40 CM, it should tune on 6 M and be about 60 %
> > efficient on 10 M if you use around 1 inch (25mm) tubing. Also, your
> > capacitor is to large. You need about 26 pf for 10 m and half that
>on 6.
> > With a capacitor 10 times too large, tuning at the bottom of the
>range
> > could be difficult. What kind of match are you using - gamma match or
> > loop coupling? How much power do you plan to use?
> >
>
>I am using a Farady Loop

>for coupling the RF feed.
>Is there any usage of Balun and tuner should be considered?

A balun provides a BAlanced to UNbalanced (or an
unbalanced to balanced) transformation.

You only need one if your antenna coupling is balanced
is unbalanced and your feeder is balanced.

> From my calculation, with the velocity factor of 0.66,

Where did you get that from? The velocity factor is one
in free space - are you operating in some sticky liquid?

>or 54Mhz
>frequency. The loop diameter for 1/4w will be about 29cm. Is this
>correct? I use this formula, 300/54=5.55, 5.55/4=1.388,
>1.388*0.66=0.916, 0.916/pi=29.1cm.
>
>I am using a 12mm microwave coax cable for the loop.

If you are calculating the loop dimensions using the
velocity factor of your coax, remember that the loop is
radiating from the outside of the conductor and this
has nothing to do with what is happening inside the
coax (otherwise, how would coax feeders work?)

Regards, LenW
--
From Yahoo! Groups Help: ... trim all the irrelevant quoted text
out of your message (as a courtesy to the other members of
the group to make the digest easier to read).
• Brief Off topic comment -- Feels lit it some days... I liked your sticky liquid question, ... but mostly because I feel that is what I am operating in most
Message 5 of 21 , Aug 1, 2007
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Brief Off topic comment -- Feels lit it some days...

I liked your "sticky liquid" question, ... but mostly
because I feel that is what I am operating in most of
the time... slogging along... slowly... inexorably...

Life is highly viscous.

Happy trails. /// Richards ///
==============================================================

Len Warner wrote:
- are you operating in some sticky liquid?
>
==============================================================
• I live in an apartment 13th floor above the ground. I plan to install the loop antenna on the balcony. Although I can install a vertical antenna, I think it is
Message 6 of 21 , Aug 1, 2007
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I live in an apartment 13th floor above the ground. I plan to install
the loop antenna on the balcony. Although I can install a vertical
antenna, I think it is wiser to go loop due to it's size.
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