[time-nuts] On choosing reasonable synthesizer PN requirements

[Karen Tadevosyan]

Hello Bill,

 

Thank you for the clarification. It is especially pleasant that our opinions
are 100% the same.

However, I would like to find some tool for calculating the balance of the
radio link in order to understand exactly the reasonable requirements for
synthesizer's PN. 

The issue of stability is now gone - I use a good OCXO with the well-known
Allan deviation values
(http://www.ra3apw.ru/wp-content/uploads/2020/04/OCXO_Allan_dev_photo-768x48
3.jpg &
http://www.ra3apw.ru/wp-content/uploads/2019/10/OCXO_AllanDeviation_1-768x37
4.jpg ) and sufficient stability is confirmed by the successful work in FT8
mode via QO-100. 



Regards,
Karen ra3apw

 

>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