Re: New antenna, new loggings


I've spent hours looking over Gary's work on all those tuned loops. That is a great resource, and must have taken a long time to build all of those.

The formula Bruce Carter put up gives a 12 turn 24 inch square loop about the right inductance with 0.5 inch spacing. I tried a few other spacings, and I can't quite follow the effect. I could also add a cap when I wanted too. I have one of those with a built in gear reduction, sold for use in crystal sets which max's out around 400 pF If I remember correctly,
For the DSP radios, I'd like to let the internal vari-cap or what ever it is, match or tune the loop. On my G8, tuning the TERK or SAT is difficult because the sampling rate for the meter is so slow, and you have to keep retuning the radio to adjust. I find that more difficult than tuning a Regen set! - FARMERIK

--- In ultralightdx@..., "osage_archer" <timchandler2001@...> wrote:

Don't forget Gary's article in this group's Files section, on PVC loop antennas:

This calculator may also prove useful although it does not apparently take into account "distributed capacitance" when the windings are closer together, but with .5 inch spacing you are probably not affected that much:

Tim C.

--- In ultralightdx@..., "farmerik" <farmerik@> wrote:

Still thinking! The circumference of a 30 inch loop is quite similar to the perimeter of a 2 foot square, does changing the shape make much difference?

If my memory of High school geometry is correct, a round loop form could be made from a strip of Masonite 8 feet long which would be close to 30 inches. Of course it would need 'spokes' or spreaders to KEEP it round. A 2 foot square loop should be easier to make, if it is just about as good.

It's Electronics 101, but I still don't have a clear understanding of the difference of Impedance and Inductance. Do you happen to know of an Impedance calculator for loops this big? What I am wondering is there transmission line I could use to mount the loops in the attic, pointing in a few different directions, and choose the one I want by connecting it to the radio separately. I just have no idea if that is possible or impossible. - FARMERIK

--- In ultralightdx@..., "farmerik" <farmerik@> wrote:

OK, now I am getting somewhere, at least in my mind. A 30 inch diameter, with 1/2 inch spacing [I think I need that to prevent capacitance between windings?] gets me to 258 uH with 15 turns and the wire I chose.
Now I need to think of a coil form that big. Sonotube? Made up from long strips of Masonite? If I can't come up with a round form, would you happen to know how to calculate for a square one?


--- In ultralightdx@..., "jim_kr1s" <jkearman@> wrote:

--- In ultralightdx@..., "farmerik" <farmerik@> wrote:

Thanks for the additional explanation, it is clearer to me now.
What sort of loop would I wind if I wanted to connect it directly, and
not use a torrid [or other] transformer?

In that case, the inductance of the antenna has to resonate directly
with the varactor diode on the chip. Taking into account stray
capacitance in the connecting wires and the loop itself, design for
about 240 uH. This calculator should get you close.
<> It
gives more accurate results for large air-loop coils than the one called
"Professor Coyle."


Jim, KR1S <>

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