[time-nuts] RF mixers for oscillator characterization, some questions

Magnus Danielson magnus at rubidium.dyndns.org
Sun Apr 19 23:20:30 UTC 2009

Bruce Griffiths skrev:
> Arnold
> Arnold Tibus wrote:
>> Bruce, 
>> a very good summary!
>> I do not know where I can get the proposed MinCircuits DBM 
>> here, I looked to all the big and international well known 
>> supplier of electronics parts with negativ result. 
>> If I have to import them from USA they could end up even above 
>> 100 $ ea. we have in Europe to take the high shipment costs 
>> and the 19% VAT into account.  
>> Is it likely to get used mixers with damaged diodes?
>> Did somebody alredy look inside the metal case of the 10514A?
>> Will it perhaps possible to reconnect the common ground connections 
>> such a way that the mentioned loops can be opened?
> Not without changing the IF port connector or at least insulating its
> shell from ground.
> It may be easier just to construct you own mixer if you cant easily
> obtain the PCB mount Mincircuits mixers that have separate IF and RF
> grounds.

Bruce, many SMD mixers also have separate LO, IF and RF grounds. It is 
just not documented in the datasheets. The recommended footprint pattern 
(on say RMS-5+) actually ties them together. The MiniCircuit SMD mixers 
I have been able to investigated (some of them have open bottom, so 
looking in just takes a sharp eye) is not hooked up with a internally 
forced common ground. A simple DC resistance measurement would indicate 
if a particular model has their grounds connected together, but really, 
they should fix their datasheets. I guess it just haven't been important 
for them before.

> Another alternative is to use a couple of RF transformers to isolate the
> mixer common ground from the RF source grounds and just have the mixer
> IF port grounded via its coax cable.
> If necessary you can easily wind you own RF transformers if you can
> obtain suitable ferrite cores.
> I thought that there was a Minicircuits distributor in
> Germany(http://www.municom.de/products/products960.php).
> Ulrich may know more about this.

Actually, MiniCircuits web indicates two.


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