[time-nuts] Re: Ublox NEO-M8T-0-10​as a LO question

[Lux, Jim]

On 3/29/21 10:14 AM, John Ackermann N8UR wrote:
> That's probably a really bad idea.  The phase noise from the TIMEPULSE 
> output is pretty bad compared to a "real" RF source, and by the time 
> it's multiplied up to 10 GHz you'll have more noise than signal. 
> Attached are some phase noise plots and a couple of spectrum analyzer 
> captures to give you some idea what to expect.
>
> BTW, even the Bodnar unit may not look too good at 10 GHz -- remember 
> that you increase phase noise by 20 dB for 10 times multiplication.
>
> John
>
What's the signal bandwidth from Es'Hail?

The optimum strategy is a *very quiet* crystal oscillator that you 
discipline with the 1pps, and choose that oscillator so its frequency is 
what you need.

What we've done in the past is use the reference to clock a NCO in FPGA, 
and use one of the well known spur reduction techniques that pushes the 
spurs away from the center before running it to the DAC. This degrades 
the performance at, say, 100kHz away, but improves the performance 
within 1 kHz. This relies on knowing what the loop bandwidth is in your 
10GHz LO PLL, since inside that bandwidth it's the reference, but 
outside it's the DRO or GaAs oscillator.


There might be some DDS chips that implement this kind of thing - the 
latest chips from ADI are pretty sophisticated.




>
> On 3/29/21 12:25 PM, Chris Wilson wrote:
>>
>>
>> Â Â  29/03/2021 17:20
>>
>> Can I use my Ublox NEO-M8T-0-10​  as a LO for  a  modified satellite 
>> LNB on 10 GHz? It needs 25 MHz and the Ublox is my only GPS locked 
>> source for such a frequency. I want to receive the Es Hail downlink 
>> with excellent stability. I can lock the receiver to 10 MHz which is 
>> available from my Trimble Thunderbolt. If the Ublox would do I would 
>> not have to buy something like the Leo Bodnar GPS. Thanks.
>>
>
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