[time-nuts] Tektronix FCA3103 ADEV measurement tau setting problem

gandalfg8 at aol.com gandalfg8 at aol.com
Tue May 29 14:58:31 EDT 2018

I have a Tek FCA3103 300 MHz counter that measures ADEV

as a built in function.  When I bring up the settings
menu for the measurement, it has an entry window for
"tau" (the averaging time, IE "sigma sub y of tau").
It defaults to 200 ms.  I can enter larger values and
ADEV gives reasonably results.  However, if I enter
smaller values, even 199 ms, I don't get any error
on the display, but I get clearly erroneous
results for ADEV. I read the manual and cannot find
anything to the effect that the instrument doesn't work
for less than 200 ms.

BTW, I asked Tek "customer no support" about it and
they were clueless.

Hi Rick,

The Tek FCA3100 is a rebadged Pendulum CNT91 and Pendulum became part of Spectracom.
Unless I'm missing something, the FCA3103 is the FCA3100 with 3GHz input C fitted.

I've also found that Tektronix tech support seemed to know very little about these but, in the past anyway, found Spectracom in the UK to be very helpful. I'm not sure about the current status as Spectracom now seems to redirect to Pendulum as a separate company again.

Unfortunately, I can't help with your enquiry, and am also somewhat confused, as I don't recall seeing a settings entry window for "tau" as a settings option for the built in ADEV function. I take it you do mean the built in option as in displaying results on the built in screen, or are you also using some external software?

If you are just usin the built in display I'd be interested to hear what firmware version your FCA3103 is showing in the "About" screen

My FCA3100 is showing the firmware version as 1.28s of 25 Aug 2010, which seems to match the latest available Tektronix download but I'm wondering now if there are unlisted updates.

Nigel, GM8PZR

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