At 12:49 PM 6/23/2003 -0400, you wrote:
>I received my HP Z3801 last week. To keep things on topic, the intent is to
>use it as an external reference for my RX340.
It's RF related and that's close enought for me!!!
As one of those 'radio guys' at the tower sites, I see these GPS antennas
frequently. Paging services use them for syncronization of their
transmitters. Cell carriers use them for E911 calls and many broadcast
stations use them for their frequency standard. 30' feedlines are common
and 50' runs are not uncommon. For shorter (<25') runs 1/4" hard line is
the norm and out to 50' 3/8" is often used. As with any tower/cell site
installation, a Polyphaser lightning protection device is in line at the
shack entrance. The antenna is typically mounted to the eves of the shack,
on the ice bridge or low on the tower. As long as there is a clear view of
the sky, life is good. The antenna itself is always in a radome to shelter
it from the weather.
When running the feedline for the antenna you need to remember a couple
things. Unless you want to replace the feedline every 6 months, go with
Andrews hard line. It is always weather tight. Use coax seal on any
connections outside. Connectors are never weather tight. SO239/PL259
connectors are OK for the "DC" bands. ;-) GPS signals are getting real
small are very picky about mismatches in impedence. Use N (or maybe TNC)
connectors until you get to the BNC on the HP. UHF connectors never were
designed to maintain an impedence match. Also remember you are sending a DC
voltage up the feed line. Poor connections will cause a voltage drop that
the patch antenna is unhappy about. (Also remember this when putting the
Polyphaser in line. It must be the type to pass the DC as well as low GHz
signals.)
Good luck es 73 de KD4GT
|