[TowerTalk] Sharing a GPS Antenna

[Jeff DePolo]

> I'm toying with the idea of trying to share a single PCTEL GPS antenna
> three-ways.
> 
> I would prefer to NOT have to put up three different GPS 
> antennas, have
> three different feed lines coming into the shack, et al.

Most purpose-built GPS splitters have diode-steering for the DC from each
port to the common (antenna) port, so if you hook up multiple GPS receivers
that each source voltage for powering the LNA in the antenna, it will simply
pull current from the one with the highest voltage and/or pull from multiple
sources depending on the IR drops involved.

If you don't want to spend the money for a real GPS splitter with a Z0 of 50
ohms such as those made by Symmetricom, MiniCircuits, et al, you can likely
get by using 75 ohm splitters (with F connectors), but the ones you'll want
to look for are made for commercial satellite receiver distribution, not the
generic type often used for cable TV.  The satellite type will have DC pass
on all ports as described above, or some will have DC pass on one port only.
The commercial ones will be rated for a minimum of 950-1450 MHz (L-band),
and many will be rated to 2150 or 2500 MHz which is even better.

Example:

http://www.markertek.com/product/201-234 (one port DC pass)

The LNA in most GPS antennas has plenty of gain to drive any reasonable
length of cable and overcome the splitting losses.

						--- Jeff WN3A


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