K6JRF's Page formerly W6FZC ESSB Audio Techniques Page |
This Technical Note details how to eliminate RFI problems w/ CMOS and LCD
electronic ckts. The case here is a LCD AC Line Voltage Monitor.
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I guess that we all have RFI problems with electronic ckts at one time or another. It goes with the territory. This note shows how I eliminated some major RFI problems w/ a LCD AC Line Voltage Monitor. Recently, I decided that monitoring my 240Vac line voltage would be handy b/c of the heavy load that is placed on this service in my shack. The FT-2000, YO-301, TS-711 and FT-1500 Linear amp are all connected to the 240Vac line. When all are operating, the line sags a bit so a line monitor would show me what happens. Easy enough you would think! ![]() ![]() After the LCD AC Monitor arrived, it was connected to a standard "zip-cord" line plug, the readings varied when transmitting. Based on where it is located, it is in a very high RF environment and reads anything from 100Vac to 390Vac. A 0.01uF, 1KV disc capacitor was added close to the input along with three (3) clamp-on ferrite chokes. All of this helped but there was still over 40Vac variance in the readings. ![]() So I constructed a "copper-house", using 4 mil copper tape, to act as a shield. The ground was soldered to the top of the house to ensure that it acts as an RF shield. The RF currents are now "common-mode" to the ckt so there's no interference. The "hole" is for readout voltage adjustment. Copper tape can be obtained here . Recommend that you get the 8" width tape. ![]() ![]() |