[time-nuts] UCCM arrived

Bob Camp kb8tq at n1k.org
Sun Nov 27 09:14:36 EST 2016


You have a system with cascaded gains and noise figures. The “front end” of the GPSDO is 
in the antenna. The cable is between the front end of the receiver and the rest of the “radio”. 
With a cascaded noise figure situation, as long as the noise figure of the first stage is low (it is)
and the gain of the first stage is high (it is) and the noise of the next stage (in the GPSDO) isn’t 
awful (it’s not) there is no problem. The gain of the antenna is specified so you know what that is.
If the cable loss is less than the gain by about 6 db, there is little impact. In this case “little” means
that you can’t measure what the impact is. Since you have a 26 db antenna, the cable loss needs 
to be less than 20 db. If you can get it down to 16 db that would give you a bit of margin.


> On Nov 27, 2016, at 2:01 AM, David J Taylor <david-taylor at blueyonder.co.uk> wrote:
> Hello to all,
> I connected the unit to a 11m of H-155 cable(assumed 4.79dB loss "worst case" at 1.5GHz), thrown the GPS antenna on the balcony horizontally and this is what I got:
> []
> - Given the attenuation (less than 5 dB) do I really need to change the cable for something better?
> []
> Giuseppe Marullo
> =====================================
> Giuseppe,
> Most GPS antennas have an LNA built-in, making cable loss less significant. Doesn't your antenna have that?
> 73,
> David GM8ARV
> -- 
> SatSignal Software - Quality software written to your requirements
> Web: http://www.satsignal.eu
> Email: david-taylor at blueyonder.co.uk
> Twitter: @gm8arv 
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