[time-nuts] HP10514B Mixer Terminations

[Brian, WA1ZMS]

Bruce is correct. For best RF performance in an "rf" environment
the use of 50ohms for all ports is a
good start. However, even in RF designs
you can often optimise a mixer spec
with something other than 50 ohms.

With a VLF IF freq like a DMTD, each
mixer model might have an ideal
termination impedance. Steve Mass' book on RF mixers is good for typical
mixer applications but the NIST papers
are better for DMTD uses.

In the mm-wave work I have done, the
first place to start is to increase LO
power until the s11 of the IF port starts
to look like a good match for the IF pre-amp. So each application of a mixer
can often be based around what you
are doing with it.

Each time I use one, I learn a new
fact! :-). Great hobby!

-Brian, WA1ZMS/4

On Sep 9, 2012, at 4:41 PM, Bruce Griffiths <bruce.griffiths at xtra.co.nz> wrote:

> David Kirkby wrote:
>> On 9 September 2012 18:28, Pascual Arbona<p.arbona at securimar.com>  wrote:
>>   
>>> 
>>>             Hello Brian,
>>>              I am a radio amateur and and also in the Time nuts list,  At the moment I am planning to bild a DMTD for experimentation. and as you have a nice experience in this field , for me will be very wellcame your help. My ask is ¿whitch is te best temination for the mixer? (FI 10Hz or 100Hz)  ¿what about the amp, limiters and zero crosing detec.)
>>>     
>> Mixers should be terminated in 50 Ohms - at least at all frequencies
>> where there is an output. Someone mentioned minicircuits. They sell
>> constant impedance filters, where the impedance in the both the
>> passband and stopband are 50 Ohms. Most filters have a impedance far
>> away from 50 Ohms in the stopband.
>> 
>>   
> This is an often repeated fallacy.
> For low IF frequencies such as in a DMTD, a reactive IF termination can have the advantage of lower noise and larger IF signal slew rate.
> The resultant reduction in RF and LO port VSWR is easily corrected (at least for low RF and LO frequencies) with a series resistor and/or resistive pad.
> There are a number of NIST papers on the effect of mixer termination for DMTDs and phase noise measurements.
> The minicircuits phase detectors (actually specialised mixers) are specified for use with 500 ohm IF terminations.
>> I don't know the details of what you are trying to do, but keep in
>> mind what I said.
>> 
>> Dave
>> 
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>>   
> Bruce
> 
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