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

Tom Knox actast at hotmail.com
Tue May 29 23:50:11 EDT 2018


Actually the CNT-91 and FCA31-3 are the same, the 300 and 400MHz are just claims, both are not very useful above 300MHz but de-rated can measure 400MHz.

Cheers;

Thomas Knox

________________________________
From: time-nuts <time-nuts-bounces at febo.com> on behalf of Björn <bg at lysator.liu.se>
Sent: Tuesday, May 29, 2018 2:03 PM
To: gandalfg8 at aol.com; Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Tektronix FCA3103 ADEV measurement tau setting problem

If this is a badged CNT-91...

This is from the current spec.

”The CNT-91 features a frequency range of 0.001Hz to 400 MHz standard with options to 3, 8, 14 and 20 GHz. ”

The counter was designed while Pendulum still did R&D in Stockholm - not very far from Magnus domains. Magnus certainly knows how to do proper ADEV with that counter.

—

     Björn

Sent from my iPhone

> On 29 May 2018, at 20:58, gandalfg8--- via time-nuts <time-nuts at febo.com> wrote:
>
>
> 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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