[time-nuts] On choosing reasonable synthesizer PN requirements

[bill]

Hello Karen,
As a general rule of thumb, if uplink LO phase noise power ends up being 
at least 15-20dB below the expected kTB noise received at the satellite 
transponder, its contribution is not really significant. With -98dBc-Hz, 
on Tx, you should be in good shape because, to simplify things a bit,  
Tx SNR at the transmitter far exceeds the SNR at the QO-100 receive 
antenna.  Thermal noise from the antenna and receiver LNA will dominate 
the received signal noise at the satellite.  It's more important to keep 
your Tx frequency stable.  A GPSDO or Rb reference will be useful here.  
It's also important to keep the DL 10.45GHz receive on frequency as well 
(even more important, given the freq. multiplication up to 10GHz).

On the DL side, antenna temperature and LNA noise should be the dominant 
signal degradation factors, so good antenna/LNA G/T is all-important.

Cheers,
Bill

On 24.04.20 08:04, Karen Tadevosyan via time-nuts wrote:
> Hi,
>
>   
>
> one of the interesting HAM radio topic in Europe now is the use of the new
> geostationary satellite Phase-4A (QO-100) for analog and digital modes via a
> 2.4/10 GHz transponder.
>
>   
>
> For my transverter (input from a UHF transceiver) in TX mode I use a 1968
> MHz LO with a phase noise level -98 dBc/Hz @ 10 kHz. It is possible to do LO
> with the best parameters but every next 10 dB increases the cost and
> complicates the decision.
>
>   
>
> My question is:  How to calculate/evaluate the reasonable phase noise
> requirements of a transverter's LO which would not lead to degradation of
> the performance of 2400 MHz radio uplink and 10 GHz downlink on the Earth -
> Analog Satellite Transponder - Earth path?
>
>   
>
> Thanks.
>
>   
>
> Karen, ra3apw
>
>   
>
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