RadioBanter - View Single Post - A neat and compact way to generate RF harmonics...

April 18th 04, 12:35 PM

James Meyer wrote in message . ..
On 17 Apr 2004 10:09:22 -0700, (Tom Bruhns) posted this:

Robert Baer wrote in message ...
...
Yes, but the emphasis was on small size, and a helical resonator
allows a goodly shrinkage of volume wihout a corresponding loss large of
Q.

As compared with what? A given coil in a helical resonator will
result in lower Qu than that same coil unshielded and simply resonated
with a good capacitor.

Not so. And others have pointed that out. If you take an unshielded
coil to it's ultimate configuration you are confronted with a resonant antenna
that is loaded by its radiation resistance and that results in a *lower* Q than
a properly shielded resonator.

ONLY if it's really big. See Reg's posting in this thread on that
subject. We're talking about making things small here, like smaller
than a 1 inch diameter coil at 18MHz. The cavity for a standard
helical resonator design will ding the Q by 15% or more; for such a
small unshielded coil do you expect that much radiation? I don't.
Not even close.

Cheers,
Tom