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

John Miles jmiles at pop.net
Sun Mar 3 16:05:53 EST 2013


I do like the strain reliefs on the Pomona cables, but the cables themselves
are leaky as expected.  A couple of points:

1) If you don't have any other signal sources in your environment that are
close to your measurement frequency but not coherent with it, you'll
probably be OK with single-shielded cables.  As soon as you bring that
second oscillator into the room, though, you need to start thinking about
the effects of cable leakage.  Most people here have more than one
oscillator in the house. :)  For many types of measurements single shielded
cables are not a big liability.  Just be aware of the compromise you're
making... and don't use them when debugging a sensitive phase comparator,
let's put it that way.  

2) Other than physical stability, I have never seen any problems that I
could blame on a BNC connector that wasn't actually defective.  The shield
connection issues that Bob mentions are certainly valid concerns but they
can happen with any fittings, not just BNC.   There's no religious reason to
avoid BNCs as long as you can keep everything still.  And you shouldn't be
moving cables around during measurements in any event.

-- john, KE5FX
Miles Design LLC



> -----Original Message-----
> From: time-nuts-bounces at febo.com [mailto:time-nuts-
> bounces at febo.com] On Behalf Of lists at lazygranch.com
> Sent: Sunday, March 03, 2013 11:59 AM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] Don't use cheap cables -- a cautionary tale
> 
> I use Ponoma cables that have the strain relief. However, I don't know
about
> the cable construction itself.
> 
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