GPS Antenna

ffighter_94 · Post by **ffighter_94** » Mon Jan 05, 2004 10:41 pm

This is slightly off topic, but I am planning on mounting a GPS active antenna along with a U/V, a 2 M yagi, 800 Mhz Omni and a 70 cm yagi on a small tower (60') outside of my work shop at my house. My question is what would be the best cable to use for the GPS antenna to carry the signal 60' down the tower and then 15' laterally inside the building to where my GPS rcvr is. I am thinking of using LMR400. Any suggestions on anything better or that will work about as good for a little less $$.

Thomas

RKG · Post by **RKG** » Tue Jan 06, 2004 6:11 am

First, check the specs on your active antenna to see what its cable requirements are. Most are 50 ohm; some are 75.

In general, feedline loss is not a problem with active antennas, since the signal is amplified in the antenna itself.

Most folks today would opt for mounting a GPS head, rather than just an antenna, on the mast, and bringing GPS data (in NMEA format) down the pipe in ASCII. Check the Garmin and Northstar sites for GPS heads.

Big BOB · Post by **Big BOB** » Tue Jan 06, 2004 4:26 pm

In all of our GPS installations we use RG-142. You don't need to mount the GPS antenna that high on the tower as long as you have a clear view of the horizons.

ffighter_94 · Post by **ffighter_94** » Tue Jan 06, 2004 6:53 pm

Thanks for the replies. As far as mounting the GPS head on the tower, I am using a Trimble SK II OEM board that is providing a 1 pps output. I also am using it for an APRS project at times. So, I prefer to have the ant. cable run into the building so that I can change what is connected to it without having to go outside. As for mounting the antenna on the tower, the only reason it is going up near the top is that it is bulk head mounted (if that is the right term) to a 12"x12"x6" box that has some other stuff in it. (Rx preamp, and a few ant. relays) I have thought about changing how I have the antenna mounted, but then I have a 3/4" hole and 4 1/4" holes in the top of my what was once weather proof enclosure..... I have had several people locally suggest Rg142, so I am sure that is what I will end up using.

Nand · Post by **Nand** » Tue Jan 06, 2004 7:45 pm

For a GPS, the RG142 is rather expensive 50-Ohm cable. Unless you really need the double-shielded silver plated features of this cable, why not just use cheap RG58 instead. The losses are nearly identical. Or a cheap 75-Ohm cable as used for TV and satellite receiver systems.

Nand.

ffighter_94 · Post by **ffighter_94** » Tue Jan 06, 2004 8:59 pm

What about RG213? I have several spools of that already laying around.

Nand · Post by **Nand** » Wed Jan 07, 2004 4:19 am

If the GPS likes a 50-Ohm cable, I see no reason why you should not use RG213 since you already have it. It has less loss than either RG142 or RG50. Are connectors not going to be a problem though?

ffighter_94 · Post by **ffighter_94** » Wed Jan 07, 2004 5:02 am

Connectors will be no problem. The GPS Ant. has a SMA on the bottom of it, I am planning on a N(f) bulkhead on the bottom of the box with a Rg-142 SMA(m)- SMA(m) jumper about 9" long on the inside of the box. Then it will be Rg-213 for 75' where it will exit the wall inside a junction box in my workshop. There it will have a N(f) that I will connect to whatever I happen to be needing a GPS antenna for.