[time-nuts] 10MHz LTE-Lite

SAIDJACK at aol.com SAIDJACK at aol.com
Thu Nov 20 17:18:01 EST 2014

Hi Dave,
very good question, for up-conversion it almost always pays off to use the  
highest frequency possible in my opinion. The reason is that you get a 
noise  increase of 20log(n/m) when up-converting.

So say you have two references, one at 10MHz and one at 100MHz. Say  both 
have a noise floor or -160dBc which is realistic.
If you up-convert the 10MHz noise floor to 1GHz by using a harmonic  
converter with very wide BW rather than a PLL with limited BW, then  the resulting 
1GHz noisefloor would theoretically be 40dB higher from the 10MHz  source 
or -120dBc. That's not very good.
If you upconvert the 100MHz source, the noise floor would be 20dB better,  
or 140dBc.
For up-conversion using a PLL with limited bandwidth this would not hold  
true. Only the noise within the BW would be up-converted.
So to answer your question: its tough to say if a 10MHz or 20MHz source  
would be better.
However many oscillator vendors use the same crystal for 20MHz and 10MHz  
TCXO parts, and simply do an internal divide-by-2 inside the TCXO to get 
10MHz  from a 20MHz crystal!
In that case you would save yourself one processing step when going from  
20MHz instead of 10MHz, so theoretically the 20MHz part would be the one to  
Another consideration could be that at 10MHz you have a huge number of  
beating noise sources all around in a typical lab, the 10MHz short wave  
transmission from Colorado, other test equipment, etc etc, and at 20MHz you have  
much less noise that could beat with your source, so that would be another  
reason to use 20MHz if you can in my opinion.
In a message dated 11/20/2014 13:40:37 Pacific Standard Time,  
drkirkby at kirkbymicrowave.co.uk writes:

For a general purpose lab source, to feed things  like

* 22 GHz spectrum analyzer
* 4.5 and 20 GHz signal  generators
* 3 and 20 GHz VNAs
* 20 or 40 GHz frequency counter (I'm  just looking to buy one)

what would you think is the best one to get -  10 or 20 MHz ? Or toss a 

Dr. David Kirkby Ph.D CEng  MIET
Kirkby Microwave Ltd
Registered office: Stokes Hall Lodge, Burnham  Rd, Althorne, Essex, CM3 
6DT, UK.
Registered in England and Wales, company  number 08914892.
Tel: 07910 441670 /  +44 7910 441670 (0900 to 2100 GMT only please)

On 20 November 2014  20:32, S. Jackson via time-nuts <time-nuts at febo.com> 
>  Hello everyone,
> after what must have been the longest thread  in T-nuts history its  
> all quiet today. I am going to take  advantage of that and  announce some
> good news:
>  Its a miracle: the 10MHz DIP-14 TCXOs for the LTE-Lite came in weeks   
> of schedule from the factory! And they work very  well.
> We will thus be shipping out the 10MHz LTE-Lite eval  boards in the  next
> couple of working days. There are still a  number left for sale on Ebay
> (search for "LTE Lite GPSDO"), so if you  were hesitant to get one due to 
the  long
> lead-time, then now is  your chance.
> Also, after being in time nuts hands for almost a  week I am surprised
> there are very few mails, questions, or comments  about the 20MHz boards, 
 and we
> have received almost no feedback  on Ebay :( I hope that is a good  sign.
> Bye,
>  Said
>  _______________________________________________
> time-nuts mailing list  -- time-nuts at febo.com
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