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

[Bob kb8tq]

Hi

…. a very normal way to get to 10 GHz is to lock up a low noise VHF oscillator
as a “cleanup” device. This is true even with a very good 10 MHz source. The
20 log N stuff simply beats you up to much. 

Some math:

A really good 10 MHz source might be in the -170 dbc/ Hz range far removed from carrier.
That gets to -150 with an ideal multiplication to 100 MHz. Any more “normal” source will
be worse than that 10 MHz OCXO. The 100 MHz will be even worse as a result. If your 
source is in the -140 to -150 range, the output will be -120 to -130 dbc/ Hz.

For not a lot of money, you can get small VCXO’s at VHF with pretty good noise numbers. 
A part that hits -160 dbc / Hz at 10 KHz offset is not all that unusual. That will give you a 
*lot* of noise reduction vs that -120 to -130 dbc/Hz. 

By the time you get to 10 GHz, you add another 40 db to the 100 MHz numbers. -120
goes to -80 dbc/ Hz. That’s a lot of noise ….

Bob

> On Mar 29, 2021, at 1:14 PM, John Ackermann N8UR <jra at febo.com> 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
> 
> 
> On 3/29/21 12:25 PM, Chris Wilson wrote:
>>   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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