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

On 2 Jul 2004 17:39:05 -0700, (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?

The 2 meter band is about 146 megaHertz. GPS uses a frequency of
around 1.2 gigaHertz.

Not many antenna designs can handle a 10:1 frequency range, especially
with such high frequencies.

There are external antennas available for some GPS units, but most
have a built in antenna,

There is a type of GPS receiver, sometimes called a "mouse" type,
which has no display or processor iteself, but must be attached to a
laptop or PDA in order to work.

Happy trails,
Gary (net.yogi.bear)
------------------------------------------------
at the 51st percentile of ursine intelligence

Gary D. Schwartz, Needham, MA, USA
Please reply to: garyDOTschwartzATpoboxDOTcom

Here's a great chance to be on the cutting edge ... try it and tell us how it
worked out!

Marconi pushed the envelope ... your turn!

(it wont hurt your GPS)

jw
K9RZZ

Here's a great chance to be on the cutting edge ... try it and tell us how it
worked out!

Marconi pushed the envelope ... your turn!

(it wont hurt your GPS)

jw
K9RZZ

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.

Possibly, but I doubt that it would be a good one. GPS uses
frequencies roughly 10x as high as a 2-meter rig. The 2-meter antenna
would probably not be resonant on GPS frequencies, and if it is of a
helical design or has a base-loading coil it might very well be a
_lousy_ antenna on the GPS frequency (the coil or helical winding
could act as a low-pass filter, blocking the GPS signal).

Its radiation pattern would probably have a lot of lobes pointed in
weird directions, and I suspect that the GPS signal from any given
satellite would be subject to a great deal of fading and jitter as the
vehicle and antenna move.

GPS receivers tend to use small "patch" antennas, etched into a piece
of PC-board substrate. These most often have a fairly uniform,
low-gain sensitivity pattern in the skyward direction.

Also, the GPS antennas separate from the GPS receiver are usually
"active" ones - they have a preamplifier very close to the antenna,
and boost the signal before it's fed down the coax to the receiver.
Losses in a typical RG-8X or RG-59 thin coax are quite high at 1.5
gigs, and the already-weak GPS signal could tend to be lost if not
preamplified.

The other problem with using a 2-meter antenna as a GPS antenna would
be that you'd need some pretty good form of switching, to keep the
input of your GPS receiver from being blown out when you keyed up the
2-meter transmitter.

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?

I'd guess that it was a standalone receiver. Even back then, there
were GPS receiver the size of a pack of playing cards (or smaller),
which plug into a PC's serial or USB port.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

Not only is the frequency range vastly different, (tho, the SWR LOSS's
would mean quite little extra loss from coax , in receive mode for the
GPS) BUT- the GPS uses a psudo omni directional antenna , read that an
immitation of an isotropic , relative to ALL angles, and polarizations)!
(remember that , with a verticle, a direct overhead signal will be next
to invisible)! and it take something like 4 satellites, to calculate
where you are (these are moveing FAST! Altho, think there is a ham
antenna was designed for such purpose- but SPENDY! Jim NN7K



Dave Platt wrote:
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.


Possibly, but I doubt that it would be a good one. GPS uses
frequencies roughly 10x as high as a 2-meter rig. The 2-meter antenna
would probably not be resonant on GPS frequencies, and if it is of a
helical design or has a base-loading coil it might very well be a
_lousy_ antenna on the GPS frequency (the coil or helical winding
could act as a low-pass filter, blocking the GPS signal).

Its radiation pattern would probably have a lot of lobes pointed in
weird directions, and I suspect that the GPS signal from any given
satellite would be subject to a great deal of fading and jitter as the
vehicle and antenna move.

GPS receivers tend to use small "patch" antennas, etched into a piece
of PC-board substrate. These most often have a fairly uniform,
low-gain sensitivity pattern in the skyward direction.

Also, the GPS antennas separate from the GPS receiver are usually
"active" ones - they have a preamplifier very close to the antenna,
and boost the signal before it's fed down the coax to the receiver.
Losses in a typical RG-8X or RG-59 thin coax are quite high at 1.5
gigs, and the already-weak GPS signal could tend to be lost if not
preamplified.

The other problem with using a 2-meter antenna as a GPS antenna would
be that you'd need some pretty good form of switching, to keep the
input of your GPS receiver from being blown out when you keyed up the
2-meter transmitter.


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?


I'd guess that it was a standalone receiver. Even back then, there
were GPS receiver the size of a pack of playing cards (or smaller),
which plug into a PC's serial or USB port.

Not only is the frequency range vastly different, (tho, the SWR LOSS's
would mean quite little extra loss from coax , in receive mode for the
GPS) BUT- the GPS uses a psudo omni directional antenna , read that an
immitation of an isotropic , relative to ALL angles, and polarizations)!
(remember that , with a verticle, a direct overhead signal will be next
to invisible)! and it take something like 4 satellites, to calculate
where you are (these are moveing FAST! Altho, think there is a ham
antenna was designed for such purpose- but SPENDY! Jim NN7K



Dave Platt wrote:
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.


Possibly, but I doubt that it would be a good one. GPS uses
frequencies roughly 10x as high as a 2-meter rig. The 2-meter antenna
would probably not be resonant on GPS frequencies, and if it is of a
helical design or has a base-loading coil it might very well be a
_lousy_ antenna on the GPS frequency (the coil or helical winding
could act as a low-pass filter, blocking the GPS signal).

Its radiation pattern would probably have a lot of lobes pointed in
weird directions, and I suspect that the GPS signal from any given
satellite would be subject to a great deal of fading and jitter as the
vehicle and antenna move.

GPS receivers tend to use small "patch" antennas, etched into a piece
of PC-board substrate. These most often have a fairly uniform,
low-gain sensitivity pattern in the skyward direction.

Also, the GPS antennas separate from the GPS receiver are usually
"active" ones - they have a preamplifier very close to the antenna,
and boost the signal before it's fed down the coax to the receiver.
Losses in a typical RG-8X or RG-59 thin coax are quite high at 1.5
gigs, and the already-weak GPS signal could tend to be lost if not
preamplified.

The other problem with using a 2-meter antenna as a GPS antenna would
be that you'd need some pretty good form of switching, to keep the
input of your GPS receiver from being blown out when you keyed up the
2-meter transmitter.


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?


I'd guess that it was a standalone receiver. Even back then, there
were GPS receiver the size of a pack of playing cards (or smaller),
which plug into a PC's serial or USB port.

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!

No. At best, the 2 meter element will be an endfire longwire at GPS
frequencies.

I don't know the reason you wish to run both on the same antenna, but I
also needed the same antennas on my car. I have a Garmin III Plus as
the input to APRS in the car. I use a suction cup mounted external
antenna for the Garmin GPS which is about (from memory) 2.5 inches wide,
1.5 inches deep, and .4 inches thick. It works very well mounted to the
lower center of the windshield on my Jetta. I run through a duplexer
into a trunk mounted Comet UHV for the 2m APRS antenna.

tom
K0TAR

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

"Andrew" wrote in message
om...
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

Andrew -

You should investigate the usage of a mobile antenna, such as the GPSx
Survivor by Antenex, 2000-205 Bloomingdale Road Glendale Heights, Illinois
60139
http://www.antenex.com/

GPSx Survivor - Model GPSDVHF
This very durable antenna features a 26dB gain active ceramic patch GPS
receive antenna with a durable black chrome plated, shock spring protected
VHF ¼ wave antenna in one complete package.
The real advantage of this antenna is its mechanical integrity. This dual
band antenna is constructed with a fully potted heavy wall resin housing, a
one-piece solid brass mounting stud, a large diameter tapered shock spring
and a tunable 0.100" diameter 17-7ph stainless steel radiator for VHF. All
of this makes it perfect for heavy equipment asset tracking and monitoring.

It comes complete with 14 feet of RG174 terminated with an SMB connector for
GPS and 14 feet RG58A/U terminated with N connector. It is mounted through a
5/8" diameter mounting hole and secured with an included heavy stainless
steel jam nut.

w9gb