[Lowfer] RX improvements

[N1BUG]

Hi LF, Lowfer,

This winter it seems my TX is not breaking down every night so I decided 
to work on my poor RX side. :-)

The first thing I found is a ground loop (or lack of single point 
ground) causing some RX noise problems. I fixed that.

Then I discovered something which I do not yet understand. The TX 
antenna is a vertical with top hat and a big coil/variometer at the 
base. It is transformer coupled to the coax, with the coax side floating 
(no connection to ground). The RX antenna is a short vertical ("LNV") 
which is only about 15m from the TX antenna, so there is strong coupling 
between TX antenna and RX antenna.

If I disconnect coax at the TX antenna, I see less RFI on the RX and S/N 
improves. Leaving the coax connected at the antenna but disconnecting 
the end in the transmitter room does not get rid of the RFI. Leaving the 
coax shield connected at the antenna but disconnecting the coax center 
conductor also gets rid of the RFI. This seems strange to me. I don't 
understand the mechanism by which the coax is apparently injecting noise 
to the TX antenna.

Anyway, I have less interference now. Not so many strong lines and 
bright areas in the spectrum. It is difficult to evaluate real 
improvement but I seemed to be hearing better last night. I was able to 
decode N3FL on WSPR during the middle of the day which has not happened 
in the past. I have to work on a relay system so I can RX and TX without 
going to the antenna to disconnect that coax!

Soon I will undertake to replace the RX crystal LO with a GPSDO source. 
The TX already uses a GPSDO derived carrier oscillator.

I think I should try a H field loop to see if that helps. Maybe some of 
these local interference sources are stronger in the E field? The 
e-Probe I built was completely useless in this environment...

73,
Paul N1BUG FN55mf