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

[Don Latham]

Noise bursts come from the rubbing of the shield on the dielectric. Try
putting some rg58 on the input of a guitar amp :-)
Even "low-noise" rg58 type coax is noisy; it has some graphite on the
dielectric supposedly to suppress the triboelectric (rubbing) noise. You
might think Teflon would be quiet, but not so.
Don

John Ackermann
> 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" <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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-- 
"Neither the voice of authority nor the weight of reason and argument
are as significant as experiment, for thence comes quiet to the mind."
De Erroribus Medicorum, R. Bacon, 13th century.
"If you don't know what it is, don't poke it."
Ghost in the Shell


Dr. Don Latham AJ7LL
Six Mile Systems LLP
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