[time-nuts] Z3801 replacement

[Bob Camp]

Hi

Ok, so the 100 MHz cleanup oscillator hopefully will be about -130 dbc / Hz or better at 100 Hz offset. That would mean a -150 dbc / Hz OCXO is roughly a tradeoff at 100 Hz. At 1KHz your cleanup oscillator should be around -150 to -160. That would put the 10 MHz at -170 to -180 to be in the same ballpark. You will have trouble getting a divider and phase detector to hit -180, so the simple answer is to keep things cheap and roll off inside about 100 Hz or so. Spurs are an unknown, but they likely will mean you want to roll off sooner rather than later as well. 

I'd go shopping for something that's got better than -155 dbc / Hz at 100 Hz and see what you can find. The TBolt OCXO meets that, there are other OCXO's that also do so. The auction sites often have TBolt pulls for < $40. I'd stick with a modern hermetic part if possible. It'll make for fewer issues down the road. 

Bob

On Jun 28, 2013, at 10:22 AM, Jim Sanford <wb4gcs at wb4gcs.org> wrote:

> Bob:
> Thanks.
> You correctly anticipated that I will use this to lock a 100 MHz Oscillator, and either multiply or lock from there.  (I'm considering a VCXO at 1GHz as well, it would either be locked to 100 MHz or 10 Mhz.  Haven't decided yet, also considering multiplying up to 1000 and then from there to 2Ghz, 3Ghz, and 5.  Haven't decided about 10 Ghz yet.
> 
> Appreciate the info.  The units on ebay are cheaper than the VCXO I was considering (first time I looked, they were more), so will probably just do that.
> 
> Thanks again,
> Jim
> wb4gcs at amsat.org
> 
> On 6/28/2013 10:07 AM, Bob Camp wrote:
>> Hi
>> 
>> 
>> On Jun 28, 2013, at 9:45 AM, Jim Sanford <wb4gcs at wb4gcs.org> wrote:
>> 
>>> All:
>>> 
>>> My Z3801 no longer works, and I've not been able to get any new ideas on it, so am looking for a replacement.
>>> 
>>> I've come across a nice 10 MHz that has very good phase noise (-145db or so at 10 KHz offset), but costs $175 in single quantities (digi-key, I think.)
>> The OCXO in the TBolt is about -165 at 10 KHz
>> 
>>>  I was considering using one of W1GHz's boards to lock it to a jupter GPS engine that I already have.  Several people have told me this is overkill, recommending the Thunderbolt.
>>> 
>>> I've read that there are various OXCXs used in Thunderbolts, some OK, some not so good.
>>> 
>>> Looking on ebay right now, I see a Nortel Trimble NTBW50AA, a Symmetricom, NTBW50AA, and another Nortel.
>>> 
>>> Does anybody have experience with these?
>> Yes
>> 
>>>   I'm particularly interested in the best phase noise I can get.
>> Spurs are what will kill you.
>> 
>> Phase noise is about 10 db worse than the TBolt far removed. It's similar close in.
>> 
>>>  This will be station master frequency reference, and will ultimately lock stations up to 10 GHz.
>> Simple answer is to run a clean up oscillator at 100 MHz and then go from there. None of the GPSDO's have low enough spurs to really do an excellent jobs at 10 GHz.
>> 
>> 
>> Bob
>>> Thanks & 73,
>>> Jim
>>> wb4gcs at amsat.org
>>> 
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