[time-nuts] Spring cleaning and antenna placement
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
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...
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