[time-nuts] Don't use cheap cables -- a cautionary tale

John Ackermann jra at febo.com
Sun Mar 3 16:11:57 EST 2013

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.

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" <ailer2 at t-online.de>
> To: <time-nuts at 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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