Looks to me like there is an incorrect interconnect cable length. If you are
intending to tune both to the same frequency, you should see a single response,
not two.
Chuck
WB2EDV
----- Original Message -----
From: Larry Horlick
To: Repeater-Builder@yahoogroups.com
Sent: Tuesday, April 20, 2010 12:38 PM
Subject: Re: [Repeater-Builder] Sinclair C-Series cable lengths
The cavities were initially tuned individually and the loop positions set for
1 db IL. They were then coupled together using a 18.5" cable and the rods
touched up to re-establish resonance. The measured IL is now 2.9. The loop
positions were not changed after coupling. When using the RL bridge I do not
see one clear notch, but rather a notch that has a bump; kinda looks like 2
notches. This is what I always see even when cavities are factory tuned, so
I'm
confident that the tuning is OK.
On Tue, Apr 20, 2010 at 9:26 AM, Jeff DePolo <j...@broadsci.com> wrote:
> I have 2 C-Series bandpass cavities, with individual I.L. set
> at 1.0 db each. When I couple them together and measure, I
> get a total I.L. of 2.9 db. I should see something like 2.1
> or 2.2. I have measured the coupling cable and see < .1 db,
> so the cable is good. Anyone have an idea why the loss is so
> high when coupled?
Most likely they aren't tuned correctly for maximum return loss, and when
you cascade them, the resonant frequency is no longer where you thought it
was (i.e. a "detuning" effect). Have you measured the return loss of the
cavities individually?
--- Jeff WN3A
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