wrote in message
...
On Jun 22, 9:26 am, "Tio Pedro" wrote:
wrote in message
Sorry, I wasn't clear. When I listen to the SB-401 transmitter on a
shortwave receiver, I hear hum modulation. The SB-301 receiver, which
drives the SB-401, works fine.

-Dave Drumheller, K3WQ

Hi Dave

Yes, I understand. But remember you are listening to the
transmitter in the near field, which means a substantial amount
of RF is being carried on your house wiring. The hum you
are hearing may, or may not, be actually present in the
transmitter's RF output.

Tunable hum is not the result of a problem in the transmitter
signal, it is the result of RF being carried on the power
lines (common mode) causing a sixty cycle variation in the
RF received signal. The hum appears same as if the carrier
is being modulated by a signal cycle signal.

You need to have a local amateur (within a few miles)
listen to you signal to determine whether the hum
modulation is real, or is an artifact caused by RF interaction
with the shack's AC wiring.

Peter, K1ZJH