Scott Stephens wrote:

Robert Baer wrote:

Paul Burridge wrote:

On Wed, 14 Apr 2004 00:36:17 GMT, "Harold E. Johnson"
wrote:


An 8 MHz filter doesn't have to be physically large Paul,

Hi Q coils in that frequency range in compact sizes... they don't seem
to go together. :-(

A high Q resonant circuit can be rather small.
For example, i made a tunable LC with a Q approaching 1000, and it was
not the size of a garbage can (resonant cavity); it was about 5 inches
tall and about 3 inches in diameter.

That doesn't sound very small.

On one extreme, one uses standard LC parts and get fair Qs in small
size.

You can also use positive feedback (negative resistance) to sharpen Q,
if you are somewhat careful or don't mind tweaking.

Rather ingenious; ther was an IEE paper 20 years(??) ago covering the
desigh equations.
The terminology used was "Helical resonator".

The ARRL Handbook has/had a design table for them too.

--
Scott

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DIY Piezo-Gyro, PCB Drill Bot & More Soon!

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A resonant cavity for the FM band would be roughly the size of a
garbage can (which i stated); 6 inches is slightly smaller, i think.