jimbob50613 wrote:
>Jeff, I disconnected the audio line to the exciter. NO Noise, so
>then I disconnected the audio from the Rx. The noise was still
>there. The only thing left is the NRHC 3+ controller. What would
>generate noise there, Bad Cap? What should I look for? Tnx...Jim
>
This particular problem surfaces with some NHRC controllers when the
audio level to the controller is high. The particular FET NHRC has
chosen for audio muting will let some audio peaks come through when the
audio level is high, like when driven from the Vol/Sq. high from a GE
Mastr type receiver. The problem with a discrete FET mute is that you
need to keep the peak-to-peak audio levels much lower to avoid
non-linear effects of the FET. Why? As the audio tends to move the
source voltage around, it affects the conduction of the switch.
I know you state you disconnected the audio from the receiver and the
noise was still there, but I wonder if you were mistaken about actually
disconnecting the audio, or if there was any other audio source still
connected.
If audio is actually still connected and the problem is the result of
audio that is too high making the FET conduct, there are two solutions.
One is reduce the audio coming into the controller by setting the level
of the receiver control pot lower. This can result in not enough audio
getting to the transmitter (even with the TX pot full) and audio balance
can be difficult to achieve in some types of radio sets. The other
solution is to replace the muting FET with something better like a PN4393.
Kevin Custer
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