Icom SM-8 Mic to K3 Need wiring advice

[Dean44]

I have a new condition Icom SM-8 Base Mic that I would like to wire to my K3.  I have the wiring diagrams for both but the Icom diagram (and schematic) shows a separate mic ground and regular ground and I am not sure how to handle that.

If anybody has experience wiring this mic, your help would be appreciated.

Thanks!

Dean
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[Don Wilhelm-4]

  Dean,

The Elecraft microphone pinout has 2 ground pins - both 7 and 8.
I believe it is conventional to connect the PTT return to pin 7 and the
AF Ground to pin 8.
In any case, it will make no difference with the K2 or K3 because both
pins 7 and 8 are connected to ground at the board.

73,
Don W3FPR

On 10/9/2010 8:06 PM, Dean wrote:

> I have a new condition Icom SM-8 Base Mic that I would like to wire to my K3.  I have the wiring diagrams for both but the Icom diagram (and schematic) shows a separate mic ground and regular ground and I am not sure how to handle that.
>
> If anybody has experience wiring this mic, your help would be appreciated.
>
> Thanks!
>
> Dean
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
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>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
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[w9gb]

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[Jim Brown-10]

  On 10/10/2010 9:56 AM, G. Beat wrote:
> It is not unusual for newer microphones to separate the microphone  shield/ground for Audio from the DC ground used for Push to Talk (PTT) switching.

Yes, mics and mic cables are wired in a variety of ways. Some have four
conductors plus a shield.  Some have two tiny coaxial cables plus an
overall shield. Some have only two conductors plus a shield. Some have
three conductors plus a shield.

When wiring a mic to a ham rig, we must figure out which of these we
have. To do that, we must get our words straight.  The return for a mic
capsule is not MIC GROUND, it is mic RETURN or COMMON. The return for
PTT is not PTT GROUND, it is PTT RETURN or PTT COMMON.  These points
will nearly always look the same with a DC Ohmeter, but at RF they may
have significant inductance between them, and that inductance creates a
Pin 1 Problem.

Cable shields can act as receive antennas, so they can carry RF current
(like from our transmitter). The ONLY proper connection for an overall
cable shield is the CHASSIS.  If you connect it anywhere else (for
example, to a circuit board, where it wanders around and eventually
finds the chassis), you have a PIN 1 PROBLEM, which is an open door to
RFI (RF in the shack).

If you have only one cable shield, it MUST GO TO THE CHASSIS to prevent
RFI.  Even though that shield may be used for mic RETURN and PTT return,
it still must go to the CHASSIS.  Inside the radio, MIC return and PTT
return are connected to the chassis via circuit traces. Those circuit
traces are plenty good enough to carry mic audio and PTT return (DC),
but they MUST NOT CARRY THE CABLE SHIELD.  That's a Pin 1 problem.

For more on The Pin 1 Problem, see http://audiosystemsgroup.com/RFI-Ham.pdf

73, Jim Brown K9YC

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[K4TEN]

I replaced one of these yesterday with one that I picked up from TenTec.

 

Although the mentioned Heil connector is of good quality, it is quite a bit
longer than others.  I much prefer the shorter ones!

The length was enough to make a difference in my shack.

 

I think mine came on a cable I got from Julius (W2IHY)

 

Frankie

K4TEN

 

 

 

Heil Sound's quality 8-pin male Foster (circular) connector !
 
http://www.universal-radio.com/catalog/parts/4065.html 
 
 

 

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