29 November 2007

Letting the Smoke Out


I recently broke the 1st rule of electronics - "Never Let the Smoke Out". This picture shows my MFJ-705 Low Pass Filter, which decided to misbehave during a recent PSK31 transmission. The odor was intense, not just a smoky smell but a seriously awful chemical olfactory offense which somehow managed to infiltrate the entire house.

I have not figured out why this happened as the 705 is rated for high power (2500 watts) and I was only running about 50 watts. Sure, the PSK signal is continuous duty, but it doesn't seem like that should cause it to melt.

So I guess I will be testing out the famous MFJ "No Matter What" warranty. Meanwhile I'll just be grateful that the whole shack didn't burn down!

1 comment:

Bill said...

Hi Keith, From the looks of that filter I'm going to make a guess that the burned section was on the output. It got Hot, meaning probably high current. That would indicate that there may have been a very low impedance at that point. Alternately, a high swr with the hot point 1/4 wave away (or odd multiples of that) from an open circuit would produce the same result. A filter is desinged to go in a properly matched circuit. If you were using an antenna tuner, it should be on the input to the tuner, where it will see the correct impedance. Sorry to hear about the problems. Good to hear you are still very active. I get the RST club newsletter even though I was never a member. It formed about the time I left Tucson.
Bill WB0KSW