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

Bruce Griffiths bruce.griffiths at xtra.co.nz
Sun Apr 19 22:04:04 UTC 2009


Arnold

Additional German source for Minicircuits:
http://www.industrialelectronics.de/

Bruce

Bruce Griffiths wrote:
> 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.
> 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.
>   
>> Thank you Bruce,
>>
>> Arnold
>>
>>
>>
>> On Sun, 19 Apr 2009 08:51:50 +1200, Bruce Griffiths wrote:
>>
>>   
>>     
>>> Arnold
>>>     
>>>       
>>   
>>     
>>> Arnold Tibus wrote:
>>>     
>>>       
>>>> Bruce, Magnus, Pete, 
>>>>
>>>> sorry for being late responding, but the Easter Holydays ... 
>>>> they are over now :(
>>>>
>>>> Thank you for the informations giving me some more ideas! 
>>>>
>>>> I am still wondering about the specials of these mixers. 
>>>> What are their secrets, what the differences to "normal" or high level DBMs? 
>>>> Is high level a criteria?
>>>>
>>>>   
>>>>       
>>>>         
>>   
>>     
>>> The dc offset at the mixer IF output (a measure of the diode matching
>>> and transformer balance) should be low as should its drift.
>>> The real criterion is low mixer phase noise particularly at low offset
>>> frequencies.
>>> The 10514 and 10534 are reputed to have low flicker phase noise.
>>>     
>>>       
>>   
>>     
>>> Using a high level mixer as suggested by NIST does have the advantage of
>>> allowing a preamp with higher input noise to be used to amplify the low
>>> pass filtered IF port output.
>>>     
>>>       
>>>> There are some companies selling the 10514A with SMB connectors. 
>>>> I have no idea what is a good or reasonable price fore and if I am running 
>>>> into possible risks to get deaf ones, for totally around $ 100,- ?
>>>>
>>>>   
>>>>       
>>>>         
>>> That price appears significantly higher than the Minicircuits price:
>>> http://www.minicircuits.com/pdfs/ZP-10514.pdf
>>> However there is no guarantee that the modern 10514's use discrete
>>> diodes or what their flicker phase noise characteristics are.
>>>     
>>>       
>>   
>>     
>>> A mixer which has a common IF, LO and RF grounds is susceptible to low
>>> frequency ground loop noise.
>>> However you can use RF transformers at the RF and LOP ports to break the
>>> ground loops.
>>>     
>>>       
>>>> In may 2007 there was aleady a short discours about the 10514A. 
>>>> Rick mentioned that today it could be possible to build a considerably better 
>>>> design with currently available technology. 
>>>>
>>>> Does it mean it is really possible to build a DBM with currently available 
>>>> diodes, transformer cores etc. with similar or better characteristics 
>>>> as the old known commercial types? Or did he think to special chip 
>>>> designs?
>>>> Are there no real merits anymore with the famous old hp 10514A? 
>>>>
>>>>   
>>>>       
>>>>         
>>> They were widely used for such measurements and their phase noise was
>>> well characterised.
>>> You can achieve better diode matching with monolithic diode quads,
>>> however the flicker noise of such quads is reputed to be higher than
>>> equivalent discrete diode quads.
>>>     
>>>       
>>>> Would be interesting to learn more about.
>>>>
>>>> Arnold
>>>>
>>>>
>>>> On Tue, 07 Apr 2009 11:40:41 +1200, Bruce Griffiths wrote:
>>>>
>>>>   
>>>>       
>>>>         
>>>>> Magnus
>>>>>     
>>>>>         
>>>>>           
>>>>   
>>>>       
>>>>         
>>>>> Magnus Danielson wrote:
>>>>>     
>>>>>         
>>>>>           
>>>>>> Bruce Griffiths skrev:
>>>>>>   
>>>>>>       
>>>>>>           
>>>>>>             
>>>>>>> Pete wrote:
>>>>>>>     
>>>>>>>         
>>>>>>>             
>>>>>>>               
>>>>>>>> Arnold,
>>>>>>>>
>>>>>>>> I have had good experience with the SYPD series
>>>>>>>> from Mini-circuits. I have not seen any used, but
>>>>>>>> their new cost is reasonable. They do several things
>>>>>>>> well e.g. the DC offset on the units I received is
>>>>>>>> <1mV & they produce >2V p-p when driven @
>>>>>>>> +7dBm.
>>>>>>>>
>>>>>>>> Pete Rawson
>>>>>>>>
>>>>>>>> _______________________________________________
>>>>>>>> time-nuts mailing list -- time-nuts at febo.com
>>>>>>>> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>>>>>>>> and follow the instructions there.
>>>>>>>>
>>>>>>>>   
>>>>>>>>       
>>>>>>>>           
>>>>>>>>               
>>>>>>>>                 
>>>>>>> Pete
>>>>>>>
>>>>>>> These are OK except when one needs to isolate the IF ground from the RF
>>>>>>> grounds to avoid low frequency ground loop problems.
>>>>>>> The RPD and MPD through hole series are better in this regard as they
>>>>>>> allow the IF ground to be isolated from the RF grounds.
>>>>>>>     
>>>>>>>         
>>>>>>>             
>>>>>>>               
>>>>>> It should be noted that several of their SMB mixers have separated 
>>>>>> grounds, but it is not documented in their datasheets.
>>>>>>
>>>>>>   
>>>>>>       
>>>>>>           
>>>>>>             
>>>>>>> The flicker phase noise characteristics of the mixer/phase detector
>>>>>>> should be measured as some mixers/phase detectors have lower flicker
>>>>>>> phase noise than others.
>>>>>>> The termination of the IF port will affect the mixer phase noise. For
>>>>>>> offset frequencies < 100kHz a capacitive termination of the IF port
>>>>>>> which reflects the sum frequency back into the mixer reduces the mixer
>>>>>>> phase noise.
>>>>>>>     
>>>>>>>         
>>>>>>>             
>>>>>>>               
>>>>>> It essentially sees a very low impedance at those frequencies.
>>>>>>
>>>>>> My experiments with capacitive loading of mixers basically indicates 
>>>>>> that the actual low-frequency slope of an unloaded mixer does not 
>>>>>> change, but the capacitor load filters the sum-frequency (with 
>>>>>> overtones) while a resistive 50 ohm load just loads the amplitude down 
>>>>>> and gives no significant change to performance. Optimum performance out 
>>>>>> of a mixer in my experience comes from fairly high-impedance load at low 
>>>>>> frequencies with a direct capacitive loading for filtering effects.
>>>>>>
>>>>>> A non-filtered response is quite interesting to see with a fairly slow 
>>>>>> beating frequency occuring. Kind of soothing waveforms floating slowly 
>>>>>> as waves over the scope.
>>>>>>
>>>>>>   
>>>>>>       
>>>>>>           
>>>>>>             
>>>>> The effect of reflecting the sum frequency back into the mixer is
>>>>> documented in some Watkins Johnson and HP/Agilent appliction notes.
>>>>> It can be very effective even at microwave frequencies.
>>>>>     
>>>>>         
>>>>>           
>>>>   
>>>>       
>>>>         
>>>>>>> The tradeoff is that the mixer output at higher offset
>>>>>>> frequencies is attenuated by the IF port termination.
>>>>>>> Terminating the IF port in a capacitor reduces the RF port impedance, so
>>>>>>> that a low value series resistor (22 to 39 ohms - select for lowest
>>>>>>> VSWR) is then required to improve the RF port VSWR.
>>>>>>>     
>>>>>>>         
>>>>>>>             
>>>>>>>               
>>>>>> Which in improves phase-stability as reflected waves has less impact.
>>>>>> -3 dB pads have also been used by the good folks over at NIST at one time.
>>>>>>
>>>>>>   
>>>>>>       
>>>>>>           
>>>>>>             
>>>>   
>>>>       
>>>>         
>>>>> The best combination is a series resistor plus an attenuator pad.
>>>>>     
>>>>>         
>>>>>           
>>>>   
>>>>       
>>>>         
>>>>>>> Terminating the IF port with a capacitor also alters the mixer gain (as
>>>>>>> a phase detector) so this needs to be measured in conjunction with the noise
>>>>>>>     
>>>>>>>         
>>>>>>>             
>>>>>>>               
>>>>>> Well... the normal 50 Ohm loading alters the mixer gain... not the cap. 
>>>>>> But since the normation is towards 50 Ohm... ah well...
>>>>>>
>>>>>>   
>>>>>>       
>>>>>>           
>>>>>>             
>>>>>>> 10514 and 10534 mixers using discrete diodes supposedly have lower
>>>>>>> flicker noise than mixers using integrated quad diodes.
>>>>>>>     
>>>>>>>         
>>>>>>>             
>>>>>>>               
>>>>>> They however has common ground in their every day laboratory variants. 
>>>>>> There exist variants meant for production. However, they are not made 
>>>>>> out of that exquisite components, so their performance should be 
>>>>>> replicable, as have been pointed out before.
>>>>>>
>>>>>>   
>>>>>>       
>>>>>>           
>>>>>>             
>>>>   
>>>>       
>>>>         
>>>>> The B versions intended for through hole PCB mount have separate grounds
>>>>> for all ports.
>>>>> These don't seem to be as widely available as they once were although I
>>>>> have an HP10534B one.
>>>>>     
>>>>>         
>>>>>           
>>>>   
>>>>       
>>>>         
>>>>>> Cheers,
>>>>>> Magnus
>>>>>>
>>>>>> _______________________________________________
>>>>>> time-nuts mailing list -- time-nuts at febo.com
>>>>>> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>>>>>> and follow the instructions there.
>>>>>>
>>>>>>   
>>>>>>       
>>>>>>           
>>>>>>             
>>>>   
>>>>       
>>>>         
>>>>> Bruce
>>>>>     
>>>>>         
>>>>>           
>>
>>
>>
>> _______________________________________________
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>>
>>   
>>     
> Bruce
>
> _______________________________________________
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
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>
>   




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