Been there, done that a couple times. It is surprisingly easy to generate
subharmonics. All it takes is a resonant length of conductor with a
non-linear junction at one end.
http://wiki.k1ttt.net/2008%20Maintenance%20and%20Upgrade%20Blog.ashx#subharm
onics
http://wiki.k1ttt.net/2008%20Maintenance%20and%20Upgrade%20Blog.ashx#daiwame
ter
http://wiki.k1ttt.net/subharmonics/subharmonic.pdf (the generator here is
more complicated than it needs to be, I later reduced it to one diode or the
other, both are not needed)
http://www.k1ttt.net/2003towerwork.html#20msubharmonic
the simplest one was a length of jacketed hardline that wasn't grounded at
the top and bottom of the tower and must have had a puncture in the jacket
that made a poor contact and would rectify.
Don't count on turning power off doing anything as the thing generating it
can be purely passive. If it is something powered it may change the note if
it is contributing to the buzz.
David Robbins K1TTT
e-mail: mailto:k1ttt@arrl.net
web: http://wiki.k1ttt.net
AR-Cluster node: 145.69MHz or telnet://k1ttt.net:7373
-----Original Message-----
From: RFI [mailto:rfi-bounces@contesting.com] On Behalf Of Dave Hachadorian
Sent: Friday, November 11, 2016 21:13
To: reflector RFI
Subject: [RFI] Unusual subharmonic RFI
Here's the story. When I transmit a nice clean 200 watts CW on
14.060 MHz, I can hear a loud, buzzy, broad signal centered on 7.030, and I
can also hear its third harmonic on 21.090. The broad signal pretty much
wipes out the 40 and 15 meter bands.
The noise, and the amount of RF power required to trigger it, vary with the
azimuth of my transmitting antenna, and point in the direction of the house
across the street. I am sure that this signal is not coming from my radio
equipment, or from my house.
A friend walked over to the neighbor's house with a portable shortwave
receiver while I was transmitting, and the noise is definitely coming from
that house. He walked into the front yard, and the noise peaked when he was
directly beneath two satellite dishes which are mounted on the roof. One is
DISH TV and the other is DirecTV. I plan to approach the residents tomorrow
to seek their cooperation. I suspect they have also been having problems
with the malfunctioning device. If they cooperate, I plan to listen to the
noise on the shortwave receiver, and start turning off circuit breakers
until the noise goes away, and zero in on which device on the circuit is the
problem. If the breakers are labeled, I'll start with the room that has the
DirecTV and DISH receivers.
Has anyone encountered a situation like this, where a subharmonic is being
generated? I could use any other advice you can think of. I am trying to
do a multi-operator radio contest on Thanksgiving weekend, so I would like
to get this fixed as soon as possible. I'll provide more info tomorrow,
after I approach the residents.
Dave Hachadorian, K6LL
Yuma, Arizona
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