[time-nuts] Advice on 10 MHz isolation/distribution amplifier

[Bruce Griffiths]

Yes implementing an exact copy without using a hybrid would be difficult.
However for 10MHz use, its probably not too difficult since that 
isolation amplifier is intended for a 100MHz signal and the requirement 
is for 10MHz operation.

If the transistor ft's are reduced by a factor of 10 or so it shouldn't 
be too much of a problem.
At 10MHz 2N3906 and 2N3904 transistors should suffice.

Bruce

Bob Camp wrote:
> Hi
>
> Implementing that circuit without using a hybrid would be a bit of a challenge.
>
> Bob
>
>
> On Feb 10, 2010, at 11:30 PM, Bruce Griffiths wrote:
>
>    
>> Clay
>>
>> Circuit schematic for a more recent JPL isolation amplifier design is attached.
>>
>> Bruce
>>
>> life speed wrote:
>>      
>>> Avoiding transformers and inductors will make it virtually impossible to
>>> achieve very low phase noise as the dc gain from say the base of any
>>> transistor in the chain to the output will degrade the flicker phase
>>> noise. Using transformers or using an inductor to shunt any collector
>>> resistors reduces the flicker phase modulation to low levels.
>>>
>>> JPL in the past has built capacitively coupled complementary symmetry
>>> isolation amplifiers that avoid transformers but suffer from dc loop
>>> gains of around 3 or so.
>>>
>>> Using complementary symmetry can be a good way of keeping the dc current
>>> down.
>>>
>>> How much reverse isolation do you need?
>>> How low does the phase noise floor need to be?
>>> What about flicker phase noise, how low does that need to be?
>>>
>>> Bruce
>>>
>>> Right, what do I really need? I only have a really good 10 MHz OCXO crystal oscillator to distribute, so about -120 dBc at 10 Hz, -140 dBc/Hz at 100 Hz, - 150 dBc/Hz at 1KHz, and -155 dBc/Hz noise floor.  No maser or cesium clock, living in the world of practical realities here.  Of course I would like to be 3 - 6 dB better than the OCXO numbers.
>>>
>>> Reverse isolation is my primary interest in the distribution amplifier approach, although the OCXO is good enough that a sloppy approach could contaminate the phase noise also.  I would like to accomplish at least 100 dB reverse isolation at frequencies below 20 MHz, but more is better in this case.  The 10 MHz is running all over a noisy aircraft, to potentially noisy receivers.
>>>
>>> In reading up on the subject, I have come to understand that DC gain is the bane of close-in phase noise.  Given that flicker noise is such a headache for we frequency synthesizer designers, I guess this should come as no surprise.
>>>
>>> Clay (AKA Lifespeed)
>>>
>>>
>>>
>>>
>>> _______________________________________________
>>> 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.
>>>
>>>
>>>        
>> <JPL_Iso_Amp_2A.png>_______________________________________________
>> 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.
>>      
>
> _______________________________________________
> 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.
>
>