[Lowfer] UWL loop

[Bill Ashlock]

>IMO, Bill is being too conservative.  It is true that the radiation
>resistance of a small loop is proportional to the square of its area,
>so for a given antenna current the smaller loop will be 20 dB worse.
>However, the Rac of the smaller loop will be only about 1/pi as large,
>so for a given Tx power, the smaller loop is only 15 dB worse.

I forgot about the reduced Rac with size, Stewart, thanks for pointing this 
out. When you factor in ground losses you are probably more like 16 dB 
worse. As you state below you can construct a 3-wire conductor from the wire 
used to make the big loop but my data for a one inch spacing shows a 2x 
reduction in Rac or a 3 db gain in signal. This net is approximately 13 db 
worse....still not too bad for a small antenna, I guess. Spacers will have 
to be used at approximately 2ft intervals or less in order to keep the 'wind 
effect' to an acceptable amount for a loop with a Q of over 150.

Using a 3.14 'reduction factor' in the length of the loop conductor makes 
the size of the equivalent conductor for both loops, having the same signal, 
more like 6" instead of 10. I've often thought of covering a thin PVC drain 
pipe with a spiral of copper fold, soldered a long the seam. The skin depth 
at 185K is something like .003", if memory serves, so th foil wouldn't be 
too expensive.

Bob, using aluminum would be something close to an increase in Rac of 1.6X 
or a 2 dB loss compared to a copper loop of the the same dimensions.

I think I'm feeling another experimental loop coming on and I can't find the 
prevention pills.  :)
My last 'smaller loop' was made out of 8 X .82" OD pipe and was -8db 
compared to a #12  full-sized loop. I calculate 6"/.82 is a 8.6 dB gain so 
the loops would be close to being equivalent. Not exactly the hidden loop in 
the trees.  Hmmmm.

Bill

>If you made the smaller loop with the same length of the same wire
>that was used for the larger loop, you could have three strands in
>parallel.  If they were widely spaced, there would be a 5 dB improvement,
>resulting in performance 10 dB worse than the larger loop.  Closer
>spacing of the strands will, of course, degrade performance somewhat.
>My guess is that one inch spacing between strands would result
>in a loop about 11 dB worse than the big one.
>
>73,
>
>Stewart KK7KA
>
> > Not to put down the common "how am I coming in" approach, the difference 
>in
> > signal strength at a distant site for a loop with a 15M diameter vs a 
>15M
> > circumference is basically the ratio of the two areas. This assumes the 
>same
> > conductor type and both loops are at least 6ft above ground at their 
>lowest
> > point. The area for the 15m cir loop is ~180 sq M and the area for the 
>15M
> > diam loop is ~18 sq M so you are giving up 10X or 20 db.
> >
> > The only way to beat this huge deficit (forget the multistrand approach,
> > it's too unstable) is to reduce the loop conductor Rac loss by 
>increasing
> > the diameter of the conductor to the square of the loop diameter ratio.
> > Assuming 0.1" for the larger loop conductor the smaller loop would have 
>a
> > diam of .1 *100 or 10 inches!
> >
> > Bill

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