[time-nuts] GPS Antenna on Tower.

Bob kb8tq kb8tq at n1k.org
Fri Jun 16 14:38:20 EDT 2017


Will there be an effect? Yes. Are roughly 99% of all GPSDO’s run with antennas mounted that way
by “pros” ? Yes again. 

If you are setting up a reference site for high precision survey work, don’t do it that way. For a GPSDO,
you should be fine.


> On Jun 16, 2017, at 1:17 PM, Dan Kemppainen <dan at irtelemetrics.com> wrote:
> Hi All,
> Fair Warning: Nuts Mode Engaged.  :)
> Recently we've moved to a new house and am in the process of getting the antennas back up for various things. One of these is the GPSDO(s), and an obvious location is somewhere on a Roan 25 tower set up just south of the house. At about half way up the tower, there is clear sky view in all directions and the GPS antenna is temporarily parked there about a foot off the tower. The GPS antenna is on the south side of the tower and we're ~47N, so most of the GPS birds should be visible. Single band GPS antenna, nothing special.
> My guess is this will be fine. However, I'm still wondering what sorts of multi-path or reflections could be expected off the tower itself. And are these enough to worry about? If there is multi-path what sorts of things would help prevent this? (Mounting the antenna further off the tower, etc.)
> Once I get the tower guy lines redone, I'm thinking about putting the GPS antenna on the tip of the mast (No rotator on this tower). That's at about 75 feet with nothing close by. That would be slightly above the tree line, with a 360 degree sky view.
> FYI, currently the GPS antenna wire is "Priority Wire and Cable" RG-6/U. Did some measurements last night. It measures as 85 Ohm, with a velocity factor of ~.86. It looks pretty lossy, but it should still work.
> Any ideas and comments welcome!
> Thanks,
> Dan
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