On Wed, 07 Sep 2011 08:41:34 -0500, Jeffrey Angus
wrote:

MFJ isn't the only ones that can suffer at the hands of others.

I was trying to locate some interference using a UHF Yagi and
a Motorola R2018 service monitor. Do not key up a hand held in
front of the antenna. At least Motorola anticipated that, and
it took out the picofuse behind the antenna connector instead
of the front end mixer.

Well, do the math. The front end of the service monitor is 50 ohms.
The fuse is probably 0.1A. Power to blow the fuse is:
P = I^2 * R = 0.1^2 * 50 = 0.5 watts = +27dBm
I'll guess a 10dBi yagi and a 3 watt (+35dBm) HT into a 0dBi rubber
ducky.

[Q]: How close to the antenna can you use the HT before you blow the
fuse?

Go thee unto:
http://www.terabeam.com/support/calculations/som.php
and inscribe the tx power (in dBm) and the antenna gains into the
boxes. Use 0dB for coax losses and 440MHz for the frequency. Don't
worry about RX sensitivity. Plug in different values of distance
(miles) until you get an RX signal level of +27dBm. I get:
0.0003 miles = 1.6 ft

So, stay at least 1.6 ft away from your antenna and you won't blow the
fuse. Please change my guesswork to match reality and recalculate.

Drivel: Yes, I know we're close to the near field and the numbers
aren't very accurate.

Jeff-1.0

Jeff 2.0 (the upgraded version).

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558