[time-nuts] 10MHz LTE-Lite
SAIDJACK at aol.com
SAIDJACK at aol.com
Thu Nov 20 17:18:01 EST 2014
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,
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
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
> 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,
> have received almost no feedback on Ebay :( I hope that is a good sign.
> time-nuts mailing list -- time-nuts at febo.com
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