I recently built the W1 Wattmeter/SWR Bridge to use in tuning my antenna.
I've noticed that whenever I have it in-line between my K1 and the antenna, I
hear a dramatic increase in receiver noise level. The S-meter on the K1 goes
from 2 bars to 4 bars. This happens whether I have the W1 turned on or turned
off, and happens on both 20 and 40 meters.
The noise level is lower when the antenna is out of tune (it's a manual trap
antenna that requires me to manually change a wander lead and change the length
of a counterpoise when I switch bands). When I first switch bands, the noise
is down at 2-3 bars. Once I tune up the antenna with the wander lead and
counterpoise, the noise is back up to 4 bars. I believe (but can't measure)
that the level of actual transmissions is higher with the W1 in the circuit
than with the W1 not in the circuit.
The noise itself sounds like broad atmospheric QRN -- it's nothing specific,
just loud crackling as opposed to a hum or ignition noise or a specific tone.
The only other thing I can say is that I have the W1 connected to the K1 by a
3' BNC to BNC cable. The cable is coiled to sit on my desk. I have tried
stretching out the cable, but it has not reduced the noise. Similarly, I have
tried moving the W1 to various locations on my desk and off the desk without
any noticeable improvement.
My antenna is not that far from power lines, telephone lines, and cable lines
(about 10' at closest point, but positioned so that it can't fall on any of the
lines), and the W1 is not that much further away from the antenna (the antenna
is mounted to the house just outside the window of my shack).
Any thoughts as to why the noise level would be dramatically louder with the W1
in the line? Could I have done something wrong in building the W1? It seems
to be working correctly.
Obviously, I can just take the W1 out of the antenna line to eliminate the
noise, but I'm curious as to why I would be getting this effect.
Thanks.
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