[time-nuts] RF mixers for oscillator characterization, some questions
bruce.griffiths at xtra.co.nz
Mon Apr 20 00:19:18 UTC 2009
Magnus Danielson wrote:
> Bruce Griffiths skrev:
>> Hej Magnus
>> Magnus Danielson wrote:
>>> Hej Arnold,
>>> Arnold Tibus skrev:
>>>> 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.
>>> It was not too hard to find their official list of representatives.
>>> That is what I usually do besides the top catalog firms.
>>> Prices does not seem too bad...
>>>> Is it likely to get used mixers with damaged diodes?
>>>> Did somebody alredy look inside the metal case of the 10514A?
>>> You made me remember I needed too....
>>>> Will it perhaps possible to reconnect the common ground connections
>>>> such a way that the mentioned loops can be opened?
>>> Yes. The grounds is separated on the PCB, so it is only on the front
>>> plate that they actually interconnect when the BNCs screw tight.
>>> What's inside then?
>>> Well, there is 4 small torroid cores (as compared to the 10534A which
>>> has only two cores). It also has 4 diodes (marked as HP 82) and 2 50
>>> Ohm resistors.
>>> The L and R ports have an isolational transformer each, with the 50
>>> Ohm resistor loading on the secondary side. A inner transformer then
>>> follows, with two secondaries, hooked up like expected for a double
>>> balanced mixer. Essentially this is a double balanced mixer with
>>> additional isolational transformers and 50 Ohms terminations.
>> Its a little strange to terminate a mixer RF or LO port with 50 ohms to
>> ground as usually the IF port termination largely determines (together
>> with diode on impedance) the input impedance seen at the RF and LO
> I was also reacting to this...
>> Are you sure that the first transformer isnt a splitter with the 50 ohm
>> termination being the internal splitter termination?
> Yes. But looking more closely on them, they look like RF chokes, such
> that common mode is suppressed. Having an RF choke there, loading it
> with a resistor seems reasonable, as it needs to be loaded even for
> lower frequencies to be useful.
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Do you mean a common mode choke with a common mode termination or
perhaps a Guanella balun?
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