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Author Topic: loud noise and softer sound, but something is not right  (Read 871 times)
AG5T
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Posts: 162


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« on: November 25, 2012, 03:46:42 PM »

I have a weird situation where when I key up the microphone, the sound I hear in my headphones drops way off. When I move the MFJ tuner or tap on it, I can sometimes get the loud white noise you usually hear to come back. However, I am not sure which is correct and what is going on. Sometimes I can key the microphone again to get the louder sound come back. All of my equipment is quite old - the tuner is a versa tuner II, circa 1990, and the rig is a Yaesu FT-747GX, also circa 1990. To make things even more confusing, the microphone is plugged into a Rigblaster. The cable from the rigblaster to the radio looks fine. Here is the deal - the louder white noise sounds more like what you usually hear; the softer noise is much quieter and I can hear the stations, but I have to turn up the volume/AF on the HF rig. -- I have done a trace on everything from the coax coming in from the outside all the way through the antenna selector, low pass filter, etc. and just haven't been able to pinpoint what is going on. Maybe someone can figure out what is taking place.
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WD5GWY
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Posts: 403




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« Reply #1 on: November 25, 2012, 05:16:47 PM »

Bypass your switches, tuner etc. and connect your antenna directly to your rig.
(do it on a band where the antenna is resonant) Then, try keying up etc.
Since you say when you tap the tuner things seem to return to normal, I'd suggest
that you have some issues with the tuner. It may just need some cleaning or some
connections tightened a bit. Band switches etc. do get dirty and can cause problems.
I have an older MFJ tuner that has a roller inductor and over time it will do something
similar. I have cleaned the coil surface with a soft cloth and some DeOXIT (light spray
it doesn't take much) and that usually brings things back to normal.
The tuner is probably the source of your problem. But, bypassing things like I mentioned
will help rule out other things.
james
WD5GWY
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