[TenTec] Tentec 700 Hand Mic Question

[K8JDC]

Bob,

     Yes I did wire the voltage hot all the time as a test.  The power 
is definitely going thru the PTT switch but the mic is hot all the time 
if I  bypass the PTT switch.  In other words, if I use my footswitch to 
key the back-panel mic input (for digital modes or whatever), then the 
700 audio is also live if it is connected to the front of the radio.  
Now, I can obviously unplug the 700 but I was hoping to find a fix 
because I want to be able to use the front and back panel mic inputs 
interactively.  I can do this with my 701 hand mic without the spike but 
was hoping to fix the 700 so it was also usable.

Whatever transient is going on is not caused by activating the PTT 
anyway because I tried connecting the mic with the PTT switch already 
activated and it still causes the spike.  Seems like it is the 
application of voltage to the circuit and the PTT switch.

Dave



On 12/18/2010 12:26 PM, Bwana Bob wrote:
> Dave:
>
> Did you try rewiring the mic element so that it is powered all the 
> time? Maybe the mic power is going through the PTT switch and the 
> turn-on transient is putting out an audio pulse.
>
>                 73,
>
>                 Bob WB2VUF
>
> On 12/18/2010 10:50 AM, K8JDC wrote:
>> Friends,
>>
>>       I recently got a Tentec 700 hand mic and noticed that it causes 
>> the
>> radio to transmit a spike every time the PTT lever is pushed.  The mic
>> was set up to use a 9V battery when I got it but I have wired it to
>> operate directly off my Paragon II.  It spikes on either power source
>> and the spike is basically full output power so it's a bit alarming.
>>
>>       I originally thought the spike was related to the operation of the
>> PTT switch...i.e. a little clicking noise causing the spike but that's
>> not true.  If I key the PTT with the mic disconnected from the radio and
>> then connect the mic to the radio, the spike still happens so it appears
>> that it is related to applying the voltage to the mic circuit or
>> cartridge.  I played around a bit trying to add a capacitor to stabilize
>> the power in the circuit and eliminate any transients but the spike is
>> still there.
>>
>> Has anybody seen this and/or have a fix?  The existing caps in the
>> circuit appear to be okay (i.e not shorted) and I think the cartridge
>> itself is the cause of the spike.  There is a resistor feeding power to
>> the cartridge but I have not tried raising the value (yet).
>>
>> Thanks...
>>
>> Dave
>> K8JDC
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>>
>