Thread: Spotty tracks
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Old 04-28-2016, 01:26 AM
VHS VHS is offline
Join Date: Feb 2008
Location: Napa, CA
Posts: 293
Default Poor track

Originally Posted by Sam Buchanan View Post
Assuming there were no power interruptions to the system, The most common causes for intermittent beacons is poor GPS or antenna connections. The trackers themselves have proved to be quite reliable.
It looks like John's tracker is a very early single channel unit. If the GPS was purchased at the same time, its very likely that the GPS is on its way out, the first gen units did not tend to work for more than a few years.

The RV present an unusual situation for an APRS transmitter. Most people end up with a wire J-pole or similar in the wingtip. Its also installed ( Depending on your ship's attitude) largely in the horizontal plane, which massively attenuates the signal from the perspective of the vertical VHF antennae that sit on the skin of the globe ( Actually, every vertical antenna is only perpendicular to an imaginary line across and through the planet; Another antenna a mile away has a little bit more "lean" to it compared to other antenna, even though both are measurably "vertical". At any rate, the cross polarization does not help. Another peculiarity to the RV is the asymmetry of the antenna. With the antenna in one wingtip, The fuselage provides shielding that interferes with radiating to the opposite side. Some of you may have noticed good performance on a one way trip, but poor performance on the return trip, flying the reciprocal heading. Optimally a roof or belly whip is the best option. The pattern is about as isotropic as you could hope for ( assuming you are not in contact with Space Stations. I sympathize and fully appreciate what a gold plated batch it is to install new gear, especially when it means drilling or sawing a hole in the skin of your beloved ship. One of the best jobs I heard about was a guy who purchased an approved VHF (airband) antenna, installed it on the upper spine, and ran the cable to his panel, where it was brought out as a BNC connector. As far as the FAA knew, that spare antenna was for his aviation handheld as a back-up system or to monitor several channels. When flying, he plugs in his MT-AIO to the panel with an SMA to BNC cable.

p.s. Not actually dead yet!
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