I've previously encountered noise from mechanical movement of BNCs. You
can definitely see noise bursts when you move a BNC cable around.
Replacing TNC-BNC adapters and BNC-BNC cables at the analyzer with real
TNC to SMA cables, and SMA to BNC adapters on the far end when
necessary, solved a lot of those problems.
But this was the first time I've seen a continuous beat-note type of
interference that I could trace to the cabling.
As a follow-on topic -- I wonder if the leakage problem would also be
significant in a PPS distribution/measurement system (vs 5 or 10 MHz
RF). I'd think that working with pulses and using a defined trigger
level might mitigate that, but as I contemplate my rat's nest of PPS
cabling I wonder if there could still be problems.
John
----
Alan Melia said the following on 03/03/2013 03:36 PM:
Some of the older synchronised signal generators (2-box systems) e.g
Marconi, used TNC connectors with solid coax where signal leakage was
likely to be a problem.
Alan G3NYK
----- Original Message ----- From: "Volker Esper" <ail...@t-online.de>
To: <time-nuts@febo.com>
Sent: Sunday, March 03, 2013 6:49 PM
Subject: Re: [time-nuts] Don't use cheap cables -- a cautionary tale
Yes, we all have to learn that lesson...
At the time I use bedea RG-223 and Belden H155 with soldered and
crimped Telegaertner BNC connectors as general purpose cable (up to 2
GHz). Above that frequency I wouldn't use BNC. If you simply connect
your tracking generator with the spectrum analyzer by using such a BNC
cable there's not one that is absolutely stable when stressing the
connector. I tried several manufacturers, HP, Suhner, Radiall,
Rosenberger, it's always the same.
To make precise measurements I prefer screwed connectors like N or SMA.
Volker
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