[time-nuts] REF osc distribution.

Bob Camp lists at rtty.us
Wed Sep 5 22:05:41 UTC 2012


Hi

The NIST bipolar designs can indeed do better than a good quality OCXO for short term and close in phase noise. If you have a wide band floor at -185 dbc/Hz on your OCXO they aren't quite up to that level. 

Bob

On Sep 5, 2012, at 5:55 PM, Tom Knox <actast at hotmail.com> wrote:

> 
> I have seen that many commercial ref distribution amps are not as good as a quality low phase noise 5 or 10MHz oscillator, considering the time and resources that went into their design 
> I think it would be difficult to design a amp capable of distributing something much cleaner then a LPRO.  
> Thomas Knox
> 
> 
> 
>> From: lists at rtty.us
>> Date: Wed, 5 Sep 2012 17:37:34 -0400
>> To: time-nuts at febo.com
>> Subject: Re: [time-nuts] REF osc distribution.
>> 
>> Hi
>> 
>> You *can* get the job done with a CMOS inverter biased up and filtered. An op amp is likely not as good as the full bipolar approach and may be better / worse than the gate depending on exactly what you are looking at.
>> 
>> Bob
>> 
>> On Sep 5, 2012, at 12:59 PM, Michael Tharp <gxti at partiallystapled.com> wrote:
>> 
>>> On 09/05/2012 12:46 PM, Bob Camp wrote:
>>>> Hi
>>>> 
>>>> There are a number of discrete transistor buffers that have very good
>>>> isolation and short term stability / phase noise performance. I'd take a
>>>> look at the one from the NIST papers and Bruce's more modern re-design.  All
>>>> are in the archives. http://tf.boulder.nist.gov/general/pdf/498.pdf is a
>>>> pretty good place to start.
>>>> 
>>>> Mostly what they do is to run a common emitter amplifier followed by several
>>>> common base amplifiers. They may or may not follow that with a buffer. Each
>>>> channel gets a separate string of amplifiers. All the common emitter amps
>>>> are driven in parallel by the reference source.
>>>> 
>>>> The transistors used are normally cheap stuff like the 2N3904. Except for
>>>> the power supply nothing in the circuit costs much. None of it is hard to
>>>> find.
>>> 
>>> For an integrated (op-amp) solution, how does OPA830 stack up? I'm trying one out for a GPSDO design to buffer the signal from the OCXO for 50 ohm output, but I may also build a distribution amplifier at some point.
>>> 
>>> At $1.91 for single pieces on Digi-Key it's not terribly expensive, but something cheaper could probably get the job done. There are also dual and quad versions (OPA2830 and OPA4830).
>>> 
>>> -- m. tharp
>>> 
>>> _______________________________________________
>>> 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.
> 		 	   		  
> _______________________________________________
> 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.




More information about the time-nuts mailing list