[Boatanchors] Microphone

[Richard Knoppow]

----- Original Message ----- 
From: "David C. Hallam" <dhallam at knology.net>
To: "Richard Knoppow" <1oldlens1 at ix.netcom.com>
Cc: <Boatanchors at mailman.qth.net>
Sent: Friday, February 08, 2013 2:35 PM
Subject: Re: [Boatanchors] Microphone


> Well, a little more information.  I connected it to an 
> SBE-33.  What happened was when I pushed the PTT switch, I 
> got full output on the SBE-33 with no audio input to the 
> microphone.  The purpose of the walwart to to simulate on 
> the bench the voltage applied through the switch contacts 
> when it was connected to the SBE-33 while I observed what 
> was happening on the scope.
>
> I have downloaded the same file.  Looking at the switch 
> diagram in the file.  I have the microphone connected to 
> contacts 1 & 2. Contact 1 is also connected to the braid 
> shield.  PTT wires are connected to contacts 4 &5. 
> Contact 4 is also connected to the shield.
>
> David
> KW4DH
>

     First of all, the microphone contacts can be tested 
with a plain ohm meter. If you get it across the mic element 
it won't do any damage.
     Some transmitters have three terminal microphone 
connections and some have four terminals.  Where there are 
three terminals one is shield-ground, one is the microphone 
hot side, and one is the PTT contact which uses the shield 
as the common.  Where there are four terminals two are for 
the microphone element and two are for the PTT. The PTT and 
microphone do not use the same return.
     If you are getting full output when the PTT is actuated 
its likely you have an open ground for the microphone 
element. Check the leads going to the element through the 
PTT switch. They should show a short when the switch is not 
actuated and several thousand ohms when its pushed. If it 
shows an open circuit you have either an open lead somewhere 
or the voice coil is open. I suggest opening the switch and 
measuring at its connections. Check the mic element to see 
if its open (you should hear a click beside getting a 
reading) and make sure the switch is not wired wrong, i.e., 
that its wired to short the element when not in transmit and 
not somehow wired in _series_ so that its opening the mic 
lead when pushed.  You can determine all this in a few 
seconds using an ohmmeter.



--
Richard Knoppow
Los Angeles
WB6KBL
dickburk at ix.netcom.com