[time-nuts] 10 MHz phase comparison using Bruel & Kjaer type 2971 phase meter

Alex Pummer alex at pcscons.com
Sat Jan 30 22:52:28 UTC 2016

Hi Luca,
look here:  http://www.clmt.de/service-manuals/
On 1/30/2016 12:49 PM, Luca Dal Passo wrote:
> Hi All,
>      while i was looking for an hp k34-59991A phase comparator on ebay in
> order to make some long term measurements of frequency drift of a dut
> against a reference (by logging the analog output of the meter) i found and
> bought a Bruel & Kjaer type 2971 phase meter instead of the hp.
> It is a very nice unit, with digital and analog readout, high resolution
> and high precision.
> The drawback is that it is a very low frequency device, specified for the
> range 2Hz to 200 kHz.
> So, to compare two 5 or 10 MHz signals i'm thinking to use two simple
> double balanced mixer, some low pass filtering on the IF outs of the
> mixers, and a common local oscillator of about 5,1 MHz or 10,1 MHz to
> convert signals into the range of the instrument.
> The actual frequency of the local oscillator does not metter, because it is
> the same for the two input signal, and theoretically i could use even a
> simple free oscillator, provided only the frequency falls in the correct
> region regardless of phase noise and stability because their effects are
> subtracted cancelling themselves. Anyway i think to use a simple ambient
> temperature xtal oscillator for that.
> What are your opinions? What i'm forghetting to consider? What kind of
> drawback i have to expect?
> The other question is about the availability of user/service manual (or at
> least schematics) of the  Bruel & Kjaer 2971: i'm not able to find anything
> on the net.
> Many thanks!
> Luca
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