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[RFI] 40 meter intruder?

To: RFI Reflector <rfi@contesting.com>
Subject: [RFI] 40 meter intruder?
From: Cortland Richmond <ka5s@earthlink.net>
Reply-to: Cortland Richmond <ka5s@earthlink.net>
Date: Thu, 9 Sep 2004 17:23:09 -0700 (GMT-07:00)
List-post: <mailto:rfi@contesting.com>
The ARRL web site reports widely a heard intruder on 40 meters, consisting of 
closely spaced carriers at 
7238.063, 7238.150, 7238.237 and 7238.412 kHz.

These are 87 Hz apart.

063 + 87 = 150
150 + 87 = 237
237 + 87 = 324
324 + 87 = 411 (close enough)

What is significant about 87 Hz? 

"Some monitors, at this point, use a technique called interlacing to cheat a 
bit and allow themselves to display at a higher resolution than they otherwise 
could. Instead of redisplaying every line of the screen, when in an interlaced 
mode the electron guns sweep alternate lines on each pass. So the first pass, 
odd-numbered lines are refreshed, and the next pass, even-numbered lines, and 
so on. This allows the refresh rate to be "doubled" because only half the 
screen is redrawn at a time. The usual refresh rate for interlaced operation is 
87 Hz, which corresponds to 43.5 Hz of "real" refresh given the half-screen 
source: http://www.pcguide.com/ref/crt/resRefresh-c.html

My conclusion: This is 87 Hz noise coupled from a computer monitor into the rig 
of someone east of Prescott. 

Cortland Richmond

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