Minimizing transmit distance

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jantman

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Apr 1, 2005, 7:09:32 PM4/1/05
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I'll keep this simple.

I have a mobile radio mounted in my car. It's an Icom 207H 2m Mobile. I
need to somehow (as easily, cheaply, and quickly reversible as
possible) restrict the transmit distance to something quite short (say,
between 50 and 200 feet, at the maximum). What's the best and easiest
way to do this, while still keeping something that can be easily
reversed?

Will simply running the radio on low power (5W) with no antenna do the
trick, keeping in mind that the radio is inside a metal car? Or should
I somehow shield the end of the coax and/or the body of the radio?

It will only be used to transmit in fairly short bursts, say 10 seconds
max, and at the maximum one burst per hour or two.

Thanks,
A newbie,

J. Antman

ra...@jasonantman.com

Brenda Ann

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Apr 1, 2005, 7:12:49 PM4/1/05
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"jantman" <use...@jasonantman.com> wrote in message
news:1112400571....@l41g2000cwc.googlegroups.com...

A dummy load should suit that purpose.. even the best shielded ones should
have enough leakage to be heard that far.


Brenda Ann

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Apr 1, 2005, 7:12:49 PM4/1/05
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"jantman" <use...@jasonantman.com> wrote in message
news:1112400571....@l41g2000cwc.googlegroups.com...

A dummy load should suit that purpose.. even the best shielded ones should

Dave Platt

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Apr 1, 2005, 7:30:46 PM4/1/05
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>I'll keep this simple.
>
>I have a mobile radio mounted in my car. It's an Icom 207H 2m Mobile. I
>need to somehow (as easily, cheaply, and quickly reversible as
>possible) restrict the transmit distance to something quite short (say,
>between 50 and 200 feet, at the maximum). What's the best and easiest
>way to do this, while still keeping something that can be easily
>reversed?

Disconnect radio from antenna.

Connect radio to good-quality VHF-rated dummy load.

>Will simply running the radio on low power (5W) with no antenna do the
>trick, keeping in mind that the radio is inside a metal car?

It will quite possibly damage the radio's RF finals. Some radios have
good high-SWR protection, others do not. How lucky to you feel today?

Use a dummy load, and minimum transmit power. Enough RF will leak out
of the radio and coax to allow you to hear it tolerably well over
short distances, and it should pick up enough of whatever signal you
transmit from an HT to be able to receive well enough.

> Or should
>I somehow shield the end of the coax and/or the body of the radio?

*terminate* the end of the coax with a 50-ohm dummy load.

--
Dave Platt <dpl...@radagast.org> 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!

Buck

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Apr 1, 2005, 8:46:16 PM4/1/05
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On 1 Apr 2005 16:09:32 -0800, "jantman" <use...@jasonantman.com>
wrote:

There is a strong possibility that if you operate the rig with a dead
short or open for the antenna that you will kill the finals more
quickly than you think.

Use a dummy load and see if that helps. Additionally, you may get
enough 1 watt resistors to put in parallel to make up 50 ohms at 5 or
more watts. That will work well and not risk damage to your rig.

using the dummy load inside the car will probably still allow it to
ttransmit outside for quite a ways.

Good luck
Buck
N4PGW

Buck
--
For what it's worth.

Dr. Anton T. Squeegee

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Apr 1, 2005, 8:46:43 PM4/1/05
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In article <1112400571....@l41g2000cwc.googlegroups.com>,
use...@jasonantman.com says...

> I'll keep this simple.
>
> I have a mobile radio mounted in my car. It's an Icom 207H 2m Mobile. I
> need to somehow (as easily, cheaply, and quickly reversible as
> possible) restrict the transmit distance to something quite short (say,
> between 50 and 200 feet, at the maximum). What's the best and easiest
> way to do this, while still keeping something that can be easily
> reversed?

Attach a good quality dummy load to the antenna connector, and
make sure your TX power is set at low. That should keep the emissions
down.

> Will simply running the radio on low power (5W) with no antenna do the
> trick, keeping in mind that the radio is inside a metal car? Or should
> I somehow shield the end of the coax and/or the body of the radio?

If you value your radio's transmitter stages, NEVER run it without
either an antenna or dummy load. Period.

Was that not covered in your ham radio license study material?

--
Dr. Anton T. Squeegee, Director, Dutch Surrealist Plumbing Institute.
(Known to some as Bruce Lane, ARS KC7GR,
kyrrin (a/t) bluefeathertech[d=o=t]calm -- www.bluefeathertech.com
"If Salvador Dali had owned a computer, would it have been equipped
with surreal ports?"

jantman

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Apr 2, 2005, 1:38:47 PM4/2/05
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Thanks to everyone for the replies. It turns out that the whole thing
no longer matters. The idea was to use the rig to activate a nearby
relay, based off of an old, re-programmed Motorola Minitor-II two-tone
paging reciever. However, I'm having some issues triggering the pager,
so the project is scrapped.

Thanks to all for the advice. When I place my next order from one of
the dealers, I'll buy a good dummy load in case I ever need it again.

Bruce - yes, I'm sure it was covered somewhere. But I was more worried
about getting the numbers and formulas and physics for the test, and
had no problem remembering the 'easy' stuff...when taking a test at
least.

cl

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Apr 3, 2005, 12:10:17 AM4/3/05
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"jantman" <use...@jasonantman.com> wrote in message
news:1112467127.1...@g14g2000cwa.googlegroups.com...

Based on what you're saying, I have a hunch what are you trying to do, is
test the Minitor with a 2 meter rig? I am betting you were using a "PL" tone
to try to open it up to receive. Not sure what you know about Minitor IIs,
but there are probably no less than 2 reeds in it. A "single" tone, won't do
it. And you couldn't possibly switch tones fast enough to make it work. It
is milliseconds of a difference. If you'd like some help with the Minitor
II, give me a yell privately. I repair them all the time.

cl


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