[SFDXA] : K4FK station update -- new On/Off power switch, noise, etc.

[Bill]

 From Ed N4II:

Today N4IS and I (well, mostly N4IS) added common-mode chokes to the 
K4FK power lines and receive antenna coaxes, enlarged the grounding 
straps, and added an isolation transformer to the station AC supply.  
All the station 120-V AC now passes through the isolation transformer, 
which is the black box on the floor next to the right foot of the 
station operator.



*** I bring this up to point out that the isolation transformer has an 
on-off switch, which needs to be in the “on” position to power the 
station.  Please turn the switch to the “off” position when going QRT. ***



With the station upgrades, there is no detectable noise entering the 
station via the common mode on any transmission line, or on the power 
lines.  The first layer of the noise onion has therefore been peeled.  
There is, however, significant noise coming into the station from the 
antennas, i.e., the antennas are working as designed, and picking up 
noise generated externally.  Since the noise level does not change when 
the HWF is rotated, the noise source(s) are likely to be on the roof, 
near or even under the HWF. Additionally, there is (at least in the 
daytime) significant AM broadcast IMD on both 160m and 80m (and, in 
fact, going above 4 MHz), which is detectable with both the HWF and the 
transmit antennas.



The next onion layer to be peeled is to identify the IMD source on the 
roof, which we currently suspect to be a passive semiconductor junction 
– a corroded mechanical contact on a guy wire, for example.  It’s likely 
that identification of the IMD source will be a clue to the source of 
the broadband noise itself.  In a couple of weeks N4IS and I will 
conduct a fox hunt on the roof for the IMD source (and any other noise 
sources).



Additional, known, onion layers to be peeled include the identification 
of the source of the rotary machine noise that every so often starts, 
runs, and then stops, and the conventional power line noise issue we 
have on 10 and 12m (the source is to the N or NNW, and probably not too 
far away).  These will be addressed next, probably in the order I have 
presented them.



A reminder:  As a result of the tower work by N8PR and KE4PT, the 
antennas are now pointing in the correct direction, that indicated by 
the rotator controller.