GrtPmpkin32 wrote:

I'm not saying a loop can't be made to
cover the whole band with a single 10-365. I'm just saying that for
the average "box" type loops many will try to build, I don't see it
happening. I guess just general box/diamond loop info from what I see
here...

In my experience, a single 10-365pf cap has gotten me full MW coverage most of
the time on homebrew loops, just not all of them. I have a couple of MW loops
that need a switched-gang set-up like you mentioned, to get a fuller range.
But, I also have a big (nearly 3 feet across) quilting-hoop-frame loop, twelve
turns tightly spaced, with a single, tiny 10-365pf cap. Goes from nearly 500 to
just below 1850. I didn't go through any detailed formulae when I was just
experimenting with the big loop frame (I've got it put together like a Kiwa
loop, it will turn in azimuth and altitude, very helpful for nulls) so I must
have lucked out.
But those smaller 365 caps have also been perfect for crystal sets, with full
tuning range of MW, so I always figured they'd work for loop antennas in the
same range (if you've matched the inductance right) and so far, nine times out
of ten, they do.
Linus

The traditional single gang 10-365 cap' was used to tune the oscillator
in a MW radio, not a front-end preselector. The oscillator usually
operated at 455-Khz (I.F.) *above* the desired frequency. This would be
about 995-Khz for the low end (540-Khz) of the band. That's why a
variable cap' with a maximum of 365-pf is not really low enough
(practical) when you want to use it as a tuning cap' for a MW loop
antenna or preselector. This is because it has to tune down to the
actual lower limit of the MW band (540) instead of the receiver's
oscillator frequency (995) at the low end.


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