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

[Bruce Griffiths]

Hej Magnus

Magnus Danielson wrote:
> 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.
>
Yes its likely that at least some SMT mixers have isolated grounds,
however not all will.

In particular all Minicircuits SMT phase detectors appear to have a
common ground:
The bottom view of the SYPD series phase detectors (attached) seems to
indicate that all grounds are connected together internally (or at least
externally on the package).

>> 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.
>
> Cheers,
> Magnus
>
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Bruce
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