[AMRadio] frequency sweeper

Paul Christensen w9ac at arrl.net
Thu Jan 21 11:27:20 EST 2010

> "If it sweep perhaps a hundred kc at a time, and
at a rate of perhaps 10 sweeps per second,
then I would bet on OTH radar..."

More than likely, the sweeps you're referring to are created by this 


Every 18 minutes, the Department of Homeland Security is sweeping the 
ionosphere from three locations as it triangulates illicit drug activity 
involving ships and aircraft.  Here in the Southeast, we experience +40dB/S9 
sweeps starting around 6MHz up through roughly15 MHz from each of three 
synchronized ROTHR sites located in Virginia, Texas, and Puerto Rico.  The 
sweeps are constant and always upward moving in frequency.  I have developed 
an almost Pavlovian fear of the blast every 18 minutes on 40 meters.  If one 
has a pan adapter connected to their receiver, the sweep can be seen 
marching across the screen.

The next time anyone thinks someone is simply checking the SWR of their 
antenna by sweeping their transmitter's VFO, the interference just may be 
coming from DHS. The 18 minute interval is a dead giveaway.

Paul, W9AC

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