[Lowfer] Isolation transformer, Computer noise, etc.

[Mike.WE0H]

Hey Andy,

Turn the computer off and unplug the power supply. Is the noise gone 
now? Build a 1:1 broadband transformer for your feedline. That will stop 
the common mode noise you have. I did years ago, no noise now. I'd like 
to say someone said years ago that you want 4x the feedline impedance 
for the primary & secondary of the transformer.

How about this easy idea, wind 10 turns each side interweaving the turns 
on a FT240-77 core. That should be enough inductance on each side to 
work for your LF setup. You could use a much smaller core if you like 
but use -77 material. On your HF antennas, use a -43 core. Stick with a 
FT240-43 core for the typical 100-200w rig. It should work fine.

I found one other possible noise source hear many years ago and that was 
the negative terminal on my bench power supply was tied to the A/C mains 
ground. It isn't anymore.

On those audio 1:1 isolation transformers, dig inside a old computer 
power supply and find a 1:1 transformer with a whole lot of inductance 
on each side. Use that. Problem solved. My audio transformer is about 5 
millihenry each side. Been working great for 7 plus years.

Mike
WE0H