[Lowfer] A Different Loop Question

[John Hamer]

Hey Chuck,

The idea behind the capacitor is to get the loop to resonate when it is
very small relative to the wavelength. You simply calculate it like it is a
LC tank circuit using F=1/(2*PI*SQRT(L*C)). When you have a full wave loop,
you of course don't need a capacitor and adding one would reduce the
frequency it resonates at. But, what you are talking about is a little
different. I would think the thing to do would just be to use a single turn
500 feet circumference and use a capacitor to bring the resonance down to
your 630m frequency of interest. I'm not sure the LC tank circuit formula
would get you close to choosing a capacitor, because the length of wire is
going to have it's own effects with the limitation of speed electrons can
travel over that distance in a cycle, but there will certainly be a
capacitance that will give you resonance. The higher the quality loop wire
and capacitor you use will determine your bandwidth. You will probably just
have to build it and see what happens. I'm sure there is some simulation
software that can give you an idea of what would happen. It will be
interesting to see what others thoughts are on this.

John Hamer

On Sun, Mar 13, 2022 at 7:29 PM Chuck Hays <ponybike at hotmail.com> wrote:

> First, though, a comment on the LOG antenna. I have one, approximately 200
> feet circumference. I love the thing, but there are some factors to
> account for.
>
> It's a pretty "dead" antenna compared to an aerial. That's actually a good
> thing.
> What it's most dead to is noise, so although the signal is lower strength
> the
> noise is MUCH lower strength. I find that a preamp helps pull the signal
> back up
> while still not amplifying the noise much. Sometimes, however I need to
> switch
> to my transmitting vertical to dig out a weaker signal in poor conditions.
> In
> that case, just live with the extra noise. It's good for NDBs and AM dxing.
>
> I've been thinking about a loop for 630m. Most of the loop information I
> find
> online is for "small," "magnetic," or other kinds of loops besides what I
> want
> to know about. I was thinking of a full-wave transmitting loop.
>
> To be clear, I do have enough acreage to have a single-turn 630m loop!
> That would be one big loop, though and would necessitate careful layout to
> avoid crossing parts of the property that I use for other things. I then
> considered making a multi-turn loop, basically a large-diameter coil.
>
> A full wave piece of wire for 630m is over 2000 feet. In my mental model
> I'm thinking of four turns on a frame of approximately 500 feet
> circumference.
> That would be a relatively manageable square 125 feet on a side. Big,
> but smaller than a square 500 feet on a side for a one-turn loop.
>
> The thing that stumps me most is the capacitor that would be needed.
> I read that some small loops can have as little as 5 kHz bandwidth before
> some retuning of the capacitor is needed. I don't know what this loop
> would look like, but I had the second thought that since 630m is a pretty
> narrow band to begin with, I might be able to simply put an appropriate
> fixed cap in the antenna and it would not need retuning.
>
> At the moment this is a "thought piece." I'm not sure I have the energy
> or resources to put that up. I'd still like to know whether it'd work, and
> whether I have, with the best of intentions, led myself down the garden
> path.
>
> Cheers,
>
> Chuck VE7PJR/WB7PJR
> CO90ux
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