[amsat-bb] Narrowband tuning of DCI filters?

Norm n3ykf normanlizeth at gmail.com
Mon Jul 17 23:01:20 UTC 2017

Based on my testing (with a Times technologies T-100), field trial and
my (book) reading, the four pole filter will work as a bandpass
filter. It does not have the steep skirts that a resonant cavity
possesses. It will, however do some things one cavity will not.
Playing with it showed a mode where there were two pass notches with a
reject between (like the letter "W"). Looked like what would be ideal
for a repeater.

I did use the DCI in a noisy RF environment. Did work. Next trip the
resonant VHF cavity is going, the DCI is staying home. Shaking on the
plane makes the tuning slugs come loose. No fun.

The DCI slugs shook themselves loose on the return trip.

The first and last poles are supposedly to help match (couple?), in and out.

Picked up an elderly (but in cal) Sitemaster a few months ago. If
you're interested in sweeps of the DCI and for comparison, a resonant
cavity, let me know. Much nicer tool than the T-100. (Have a Narda OSL
for field cal.)

Anritsu has lots of quality application notes regarding using it's
gear. Great entertainment.

Norm n3ykf

On Mon, Jul 17, 2017 at 11:43 AM, Robert Bruninga <bruninga at usna.edu> wrote:
> The DCI brand of interdigital bandpass filters are neat for cleaning up
> reception by blocking out of band Intermod sources etc.  But they are too
> board for any effect on in band signals.
> Has anyone re-tuned the cavities to all the same frequency to see how well
> the filter performs as a narrowband filter?
> Bob, WB4APR
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