[time-nuts] Low cost SDR suitable for phase noise measurement?

Bob Stewart bob at evoria.net
Thu Aug 11 17:15:08 EDT 2016


Hi Bob,
If I understand the question correctly, yes.  The DMTDs that I've encountered so far use a zero-crossing detector and a TIC.  I wanted to build sort of a hybrid system that has a DMTD front end and an SDR back end.  It seemed to me that that would be sort of half way between a DMTD and a Timepod.  But whereas the Timepod digitizes 4 RF signals, this would digitize 2 audio signals.  It may be that it suffers all the disadvantages of both and has the advantages of neither, but I thought I'd build it and see where it leads.
As to the 1 to 10 Hz range, doesn't that depend on the heterodyne frequency you choose?  I mean, you don't have to use a 10 Hz offset, do you?

Bob
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      From: Bob Camp <kb8tq at n1k.org>
 To: Discussion of precise time and frequency measurement <time-nuts at febo.com> 
 Sent: Thursday, August 11, 2016 3:13 PM
 Subject: Re: [time-nuts] Low cost SDR suitable for phase noise measurement?
   
Hi

Just to clarify:

You are looking for a way to digitize the output(s) of the mixer(s) in a DMTD. The 
“target signal” is in the 1 to 10 Hz range.

Is that correct or are you looking for something to use instead of a DMTD? 

Bob


> On Aug 11, 2016, at 3:29 PM, Bob Stewart <bob at evoria.net> wrote:
> 
> Hi Brooke,
> It looks like I've asked a question poorly, yet again.  So, let me try again.  I have this idea of combining a DMTD with an SDR.  So, said that way, it looks like what I really need is a 2-channel audio SDR.  And having said that, maybe what I'm looking for is an external USB sound card.  Those I can find.  I can probably even figure out how to convert them to DC and supply them with a disciplined oscillator, if needed.
> 
> Bob
>  -----------------------------------------------------------------
> AE6RV.com
> 
> GFS GPSDO list:
> groups.yahoo.com/neo/groups/GFS-GPSDOs/info
> 
>      From: Brooke Clarke <brooke at pacific.net>
> To: Discussion of precise time and frequency measurement <time-nuts at febo.com> 
> Sent: Thursday, August 11, 2016 1:36 PM
> Subject: Re: [time-nuts] Low cost SDR suitable for phase noise measurement?
> 
> Hi Bob:
> 
> The SDR-IQ has a lower frequency limit of 500 Hz.
> http://www.prc68.com/I/Bats.shtml#SDRIQ
> 
> There is a mod that replaces the on board 66 MHz oscillator with one locked to 10 MHz.
> 
> -- 
> Have Fun,
> 
> Brooke Clarke, N6GCE
> http://www.PRC68.com
> http://www.end2partygovernment.com/2012Issues.html
> The lesser of evils is still evil.
> 
> -------- Original Message --------
>> A number of posts have appeared about Zynq SDRs on the "Shera revisited" thread.  So, I'd like to ask the more general question: Are there any low cost SDRs that are suitable for measuring phase noise when coupled with a DMTD?  I believe what I'm looking for is something with enough bits to work in the audio range down to DC.  Yes, I could use a modified sound card, but I'm really looking for something not sound card related.  My thought was to use a DMTD with a heterodyne frequency of maybe 5KHz.
>> 
>> Bob -----------------------------------------------------------------
>> AE6RV.com
>> 
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