[RFI] What I use to find Interference Sources

[Ron Watson]

David, Frank may not have some pictures I have and will email to you.

The RE units (238, 240A and 242 that I have) have digital filters in them that come off the IF and gate at 120 Hz. then amplified and shaped for video and audio, so the 60 Hz. components are well above any other source sounds or frequencies.

As seen in the pictures, you can make a pretty fair stab at similar results just by hooking a common O-scope to the audio output of an AM receiver, Icom 746 used in the pictures, also a comparison is the output of the Sprague 700 type units.

On the O-scope you will need to trigger on the line frequency, I have done fairly well by using a sine wave inverter in the car and triggering on it. A sweep speed of 1 ms./div gets close to the same display as the RE units but I prefer to sweep at 2 ms. (see pics). I also prefer to use a separate scope when convenience is not a big factor, triggered scopes give a lot more stable and defined view.

Feel free to email me directly with any questions.

Also attached a block diagram of an earlier RE unit.


Ronald E Watson