[TenTec] Omni VI Output Spike

[Ken Brown]

Hi all,

There is a clue here:
>  Mine does it on releasing the button on the Heil 
> HM-10 mike.  Interestingly enough, there is no spike when using the foot 
> switch.
>   
I know nothing about the Heil HM-10, so my speculation my be 
invalid....nevertheless...

The fact that using the foot switch does not result in the spike 
suggests one of the following:

1) A mechanical squeak or vibration produced by the motion of the button 
is being acoustically coupled into the microphone.

or

2) Power switching to a preamp, or condenser microphone bias is creating 
an electrical pulse that gets into the TX audio input while the rig is 
still in transmit mode.

or

3) PTT control switching current is getting coupled into the microphone 
audio.

or

4) Even if there is no preamp or condenser microphone bias being 
switched, some microphones have either a series switch or a shorting 
switch to deactivate the mic while not in transmit mode. If this switch 
transition occurs before, or too close to the PTT release, some kind of 
a pulse could get into the mic input while the rig is still transmitting.

Microphone PTT switches that switch multiple functions such as preamp 
power, mic bias or mic shorting SHOULD have the  contacts sequenced so 
that the PTT is released long enough before any of those other functions 
occur, thus letting the transmitter go off the air before any clunks or 
pulses are generated by the other switched functions. In the old days 
this was accomplished mechanically by the spacings of the various 
"leaves" of the multi pole PTT switch. These days electronic parts and 
circuit engineering are often cheaper than mechanical engineering of a 
multi pole leaf switch. So there may be a single pole switch that drives 
some simple digital circuitry which is used to control the multiple 
functions. The digital logic may not have the necessary delays designed 
into it to prevent the problem, or it may not be working right. If the 
sequencing is working right, possibilities 2 & 4 are ruled out.

DE N6KB