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[CQ-Contest] 30m contest - probably a spur

Subject: [CQ-Contest] 30m contest - probably a spur
From: W8JI@contesting.com (Tom Rauch)
Date: Sun Jan 28 21:31:53 2001
Hi Rich,

 > I've since heard 2 other stateside stations on 30m.  A few times
 > I've heard both sides of the qso.  All signals are very weak...
 > certainly weaker than expected for 30m, given the station locations
 > and time of day (night).  So I suspect they are indeed just spurs, as
 > several have pointed out.  How they are landing in 30m is beyond me.
 > Thanks to all,
 > Rich, KA8OKH

Even hearing ONE signal would be very unlikely as a transmitter
fault. It is very unlikely to be a transmitting station fault because
there are an incredible number of tuned circuits between the
oscillators in the rig and the antenna.

Even the PA stage alone has so much good low-pass filtering that
it is difficult to pass any signal out. I just had a look at my
homebrew amp, and the 80 meter second harmonic on a receiving
antenna 1000 feet away is only S-6 !  The forty meter signal is S-2.

Not only that, it can't be a harmonic because the 160 meter
harmonics do not  fall in 30 meters. It would have to be from a very
early stage in the transmitting system.

When we consider hearing more than one station, and sometimes
both sides of the contact, chances of it being in the transmitters
are less than the odds of winning the lottery!

Most likely the IMD is produced in your receiver or something in or
around your receiving antenna. It could be mixing of a strong
SWBC station removed 1.8 MHz or so from 30 meters with the
strong 160 signals. It can even be in a fence, tin roof, or any other
poor connection in your area!
73, Tom W8JI

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