[time-nuts] Difference in antennas

[Achim Gratz]

John Ackermann N8UR writes:
> One related question, especially with mixed systems -- how do you tell
> if you have optimum signal level at the receiver?

I don't think you're going to figure out an _optimum_ gain without
proper measurements along the whole signal chain.  As a proxy, the
reported SNR should stay fairly constant with changing constellation and
environmental conditions.

> Most show some sort of SNR or Cn value.  What should we look for?  What
> are the indication of *too much* signal?  One issue in particular is how
> to handle a modern GPS that expects modest antenna gain when it's
> plugged into a system with a 50dB gain antenna at the top.

That one is easy to solve with either a too long / too low quality
cable.  :-) Otherwise you may just have to add a 20..30dB damping plug
on the receiver side.  Keep in mind that a 50dB antenna typically either
would not work at all with the supply coming from that GPS module (12V
vs. 5V or even just 3.3V) or actually has lower gain because of the
lower supply voltage.  So you may need a DC block on the receiver and a
bias-Tee at the antenna as well.


Regards,
Achim.
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