[time-nuts] Outdoor GPS Antenna Selection
ve3oat at storm.ca
Mon Jan 8 16:54:12 EST 2018
I am actually using a small commercial GPS antenna with the small
(lossy!!) coax and getting good results.
It is either a Garmin or Gilsson "puck" style antenna with 15 feet of
that terrible coax, mounted on a 3 foot wooden pole at the peak of the
roof. The antenna sits on a cast-off 10 inch aluminum pizza plate
(turned upside down for drainage) for ground-plane, covered by a large
plastic funnel to keep off some of the snow. The coax is just long
enough to reach my Thunderbolt receiver in the room below the peak.
Lady Heather shows that there are almost always at least 7 birds in
view at any time and the setup seems to work fine.
You can engineer your solution for optimum results but I would guess
that, as long as you are above a certain minimum level of signal for
the receiver, you will get reasonably good performance.
... Martin VE3OAT
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Duane Wheaton wrote :
I'm selecting an outdoors antenna for a Jupiter Pico T Timing GPS
(TU36-D400-020) but don't clearly understand what "dB" rating of
amplified antenna to use. From web references, it looks like the
degree of amplification required is dependent on 1.) The length of run
of coax lead-in, combined with the characteristic loss of the type of
coax used 2.) The amount of amplification needed to increase the very
weak GPS signal to the range the receiver requires it. If I'm running
20 feet of RG-58, would a 26dB antenna be sufficient?
The datasheet for the receiver family states, "1575.42 MHz at a level
between –115 dBm and –133 dBm into a 50 Ω impedance." So the receiver
needs at max a -115 dBm signal. The typical received signal power from
a GPS satellite is −127.5 dBm. So it looks like I need to amplify the
RF signal for the GPS receiver requirements + compensate for the high
loss of the GHz signal traveling through ordinary RG-58 coax. Am I on
track, here? Recommendations?
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