In article , Andrew
wrote:

I've got a 2 meter antenna for my mobile unit, and I'm wondering if it
could double as a GPS antenna. I've got a friend, who 5 years ago
showed me how he had his laptop running MS Streets & Trips hooked to a
GPS receiver. I'm not sure if he had a standalone receiver meant for
laptop use, or somehow used his ham antenna and another receiver. Any
ideas?

Thanks,
Andrew Weber
KG4OTT

The L1 GPS frequency used by us common folks is 1575.42 MHz, a little
more than 10x 2 meters. Another minor problem is that GPS antennas (and
signals) are circularly polarized (easy to do with a patch or with
helical designs). If at the end of a cable, most GPS antennas (such as
patches) have built-in amplifiers (and filters), and expect +5 VDC
(current limited) supplied on the cable to run the amp.

You could try to use your 2m antenna at GPS frequencies by putting a
high-pass filter between it and the GPS receiver; I don't think it's
going to work very well. Already mentioned is the fact that vertical
antennas have a sharp null directly overhead. Circular polarization is
another issue. Gain (loss) at L1 is going to hurt.

But give it a try and let us know how it works!