setting up a tiny gmrs station?
 

Hi folks! General hardware question, and I may be in over my head.

One of the prime camping locations at a nearby park is unfortunately
in a valley. This has the effect of radically limiting our GMRS
radios.

Would it be at all useful to run a mobile or base antenna about
50 feet up a tree and leave an antenna line so that we can just
plug in when we're at camp to get in contact with folks out
in the bush?

The amount of info out there is overwhelming. It seems like with
the tiny (~ 1W) radios, it's going to be important to get as
low-resistant cabling as possible.

Can anyone make a suggestion as to the right hardware for the job?
Is this a scenario where I'm going to need to "tune" an antenna?
Heck, is this even worth it?

Thanks!
WB

Hi folks! General hardware question, and I may be in over my head.

One of the prime camping locations at a nearby park is unfortunately
in a valley. This has the effect of radically limiting our GMRS
radios.

Would it be at all useful to run a mobile or base antenna about
50 feet up a tree and leave an antenna line so that we can just
plug in when we're at camp to get in contact with folks out
in the bush?

Quite possibly so, if your feedline has low-enough loss.

GMRS is a UHF frequency, which propagates mostly by line-of-sight.
There's some diffraction around edges, and some amount of reflection,
but as a general rule you can expect a better signal (somewhat-better
to lots-and-lots-better) if at least one antenna is up out of the
"ground clutter".

Feedline loss, on the other hand, will work against you. Thin
feedline will eat up a lot of your transmit power and your received
signal... e.g. ordinary RG-58 will lose about 6 dB (that's 75%) of the
power in a 50-foot run. That might, or might not, overwhelm the
advantage of having the antenna up at some height.

You can get the loss down to 4 dB by using RG-8X "mini" coax.
Standard RG-8 cable will lose 2 dB, which ought not to be a problem.

A decent combination might be to use a GMRS base antenna which has a
few dB of gain, and a run of RG-8X (which is fairly light and
unobtrusive). The antenna gain and the feedline loss might just about
cancel out, giving you something roughly equivalent to what you'd get
if you were standing up in the tree with the radio :-)

Can anyone make a suggestion as to the right hardware for the job?
Is this a scenario where I'm going to need to "tune" an antenna?

If you buy a pre-tuned commercial GMRS antenna and its usual
installation kit (which may include pre-tuned radials), it'll probably
be a "wire it up and go" job, with no antenna tuning required.

Be careful to take all of the appropriate precautions - e.g. a
climbing belt/harness, safety rope, and so forth. A distressingly
large number of amateurs are killed due to failure to take proper
safety precautions when climbing towers, buildings, and so forth.

Also - for legal reasons, this sort of antenna mod can only be done to
a real GMRS radio, for which a GMRS license is required. It's not
legal to modify the antenna setup on an FRS radio.

--
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!

Dave Platt wrote:
You can get the loss down to 4 dB by using RG-8X "mini" coax.
Standard RG-8 cable will lose 2 dB, which ought not to be a problem.

Is it worth it to shoot the extra cash on LMR 400 or Heliax?

The antenna gain and the feedline loss might just about
cancel out, giving you something roughly equivalent to what you'd get
if you were standing up in the tree with the radio :-)

On the topic of antennae, I see mentions of a "no-ground-plane" antenna.
I assume I need one of these since it will be up in a tree?

Hoping to do this one without a climb. I was thinking of shooting
a guide wire over a branch and using it to haul the antenna up, with a
few wires to stake it down with.

Also - for legal reasons, this sort of antenna mod can only be done to
a real GMRS radio, for which a GMRS license is required. It's not
legal to modify the antenna setup on an FRS radio.

Right, I think FRS radios come without the removable antenna for this
very reason.

Thanks, Dave!
-- WB

Travis Jordan wrote:
lid wrote:
Is it worth it to shoot the extra cash on LMR 400 or Heliax?

Both these lines are very heavy compared to 8X. I doubt that a few db
will make or break your ability to use the radio. If the valley is
very deep, I doubt that 50' in elevation will help much either,
especially if you are trying to communicate 'over the hill'. These
are line-of-sight radios.

Another thought if you are into 'build it yourself'. There are eight
GMRS frequency pairs reserved for repeater use. Cobble together a
low-cost, solar powered GMRS repeater. Is there someplace you could
install it on the peak of a nearby hill?

You can get the loss down to 4 dB by using RG-8X "mini" coax.
Standard RG-8 cable will lose 2 dB, which ought not to be a problem.

Is it worth it to shoot the extra cash on LMR 400 or Heliax?

I doubt it, in the case of LMR 400.
No way, in the case of Heliax.

On the topic of antennae, I see mentions of a "no-ground-plane" antenna.
I assume I need one of these since it will be up in a tree?

You can either use a half-wave end-fed radiator such as a J-pole
(which needs no ground plane).

Or, you can use a quarter-wave or stacked-collinear antenna, which
does need a ground plane. Many of these will come with a set of
radials which are attached at the bottom of the radiator, and which
serve as an elevated ground plane.

Hoping to do this one without a climb. I was thinking of shooting
a guide wire over a branch and using it to haul the antenna up, with a
few wires to stake it down with.

In that case, you're definitely going to want a relatively light
feedline, since the antenna and its connector are going to have to
support the weight of the feedline all the way to the ground. I
wouldn't use anything heavier than RG-8X in this situation.

Right, I think FRS radios come without the removable antenna for this
very reason.

Correct.

--
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!

Travis Jordan wrote:
Travis Jordan wrote:
lid wrote:
Is it worth it to shoot the extra cash on LMR 400 or Heliax?

Both these lines are very heavy compared to 8X. I doubt that a few db
will make or break your ability to use the radio. If the valley is
very deep, I doubt that 50' in elevation will help much either,
especially if you are trying to communicate 'over the hill'. These
are line-of-sight radios.

Another thought if you are into 'build it yourself'. There are eight
GMRS frequency pairs reserved for repeater use. Cobble together a
low-cost, solar powered GMRS repeater. Is there someplace you could
install it on the peak of a nearby hill?

Wow! That'd be a fun little project! I'm not very talented in the
DIY department, but it doesn't stop a guy from tryin'.

I'll have to re-scout the area. Most of this is old-growth forest,
so solar might be very limited.


- WB

lid wrote:
Wow! That'd be a fun little project! I'm not very talented in the
DIY department, but it doesn't stop a guy from tryin'.

For sure!

Here's a helpful link:
http://www.gmrsweb.com/gmrsrpt.html

Have fun.

In article , Dave Platt wrote:

Also - for legal reasons, this sort of antenna mod can only be done to
a real GMRS radio, for which a GMRS license is required. It's not
legal to modify the antenna setup on an FRS radio.

At one time Radio Shack sold a FRS radio that was designed for use in
an automobile. There was a part that went in the car and an external
antenna that went outside. The part that went in the car was really
just a remote control head, with the real radio being in the base
of the antenna.

If you can find one of them and get someone to seperate them
by a much longer cable, it would give you the height that you need.

Geoff.


--
Geoffrey S. Mendelson, Jerusalem, Israel N3OWJ/4X1GM
IL Voice: (077)-424-1667 IL Fax: 972-2-648-1443 U.S. Voice: 1-215-821-1838
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