For some reason, this was sent to me rather than autox@autox.team.net.
Reply to author, not me.
mjb.
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------- Start of forwarded message -------
Date: Mon, 21 Jan 2002 20:04:56 -0500
From: Lloyd Loring <LWLoring@attbi.com>
Subject: RE: FM Transmitters
The FCC has a limit of 100 milliwatts for unlicensed broadcasting on
the FM band. Since a milliwatt is one one-thousandth of a watt that
means you can broadcast with a power of 1/10 watt without having a
license or an FCC-approved transmitter (which is required for all
licensed use.) If you have ever seen a "Mr Microphone" or similar
toys, they can have up to this power limit.
Is 100 milliwatts enough to cover a normal autocross site? Usually it
is. Not from a "Mr Microphone, of course! I have been transmitting on
FM at autocrosses where I announce (using my own gear) for about 20
years with about that power. Although the technology I use is very
old, and prone to change frequency (drift) as the day warms up, it
can be received over the entire Peru site for example, and was able
to reach all the way to the Crawford Street motels at the old Salina
airport site back in the mid-80s (at least a half mile or more.) This
with a 100 milliwatt transmitter fed from the PA and an old modified
CB antenna stuck on top of my van.
Having a good antenna placed high up helps immensely with coverage.
Choosing a frequency that has no other stations either on it or
adjacent to it helps as well. It also means you aren't interfering
with others trying to listen to a licensed station (if you do, you
are more likely to generate complaints and FCC inquiries.)
Since most autocross sites are on relatively flat terrain, with few
obstacles to line-of-sight transmissions, the odds are good that very
low, legal power is all you need. And keep in mind that even
mod/prepared drivers can benefit in the pits if they use a good
pocket FM radio, as can workers on the course.
I'm sorry I can't recommend kits or units but you might ask Howard as
the SCCA has used them at the Nationals for several years.
Lloyd Loring <LWLoring@attbi.com>
------- End of forwarded message -------
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