[time-nuts] Spring cleaning and antenna placement

Magnus Danielson magnus at rubidium.dyndns.org
Mon Apr 20 17:35:15 UTC 2009


Brooke Clarke skrev:
> Hi Magnus:
> 
> The improvement is probably due to a noise figure reduction from use of 
> the LNA if it's near the antenna rather than at the receiver end of the 
> cable run.

A number of assumptions is wrong there...

I have an active antenna (Novatel GPS 502), followed by about 30 m of 
RG-58 which initially went straight into the Z12 using only a BNC to N 
adapter.

The LNA is inserted along with a passive splitter (with DC through from 
one of the ports) at the receiver end of the 30 m RG-58. The non-optimum 
setup makes the passive splitter enter before the LNA, but the passive 
splitter is just a poor bias tee.

So I am pretty sure that the improved S/N is mainly from gain and 
secondary from improved noise figure. I don't know the noise figure of 
the Z-12 antenna input.

If I had a passive antenna this type of arrangement would be even worse, 
but luckily I didn't start out there...

Cheers,
Magnus



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