[time-nuts] REF osc distribution.

[David]

It is even more difficult when the schematic is wrong like in figure 1
where the emitter and collector of the PNP are reversed.

On Wed, 5 Sep 2012 16:26:04 -0600, Tom Knox <actast at hotmail.com>
wrote:

>
>Hi Bob;
>There are many designs I have seen employed at NIST that have low phase noise and low noise floor.  But it is often not that easy to build a working prototype that actual achieves those levels of performance. power supply design, parts layout, shielding, and part selection all play a substantial role in achieving that level of performance. 
>
>Thomas Knox
>
>> From: lists at rtty.us
>> Date: Wed, 5 Sep 2012 18:05:41 -0400
>> To: time-nuts at febo.com
>> Subject: Re: [time-nuts] REF osc distribution.
>> 
>> 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