Great explanation Bob,
One of the most common problems in audio and DC control circuits.... confusing
"shield" and "ground" then grounding the shield at both ends causing hum or RF
in the audio.
Best regards,
Gary - AB9M
CSM(r)G.L.Huber
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----- Original Message -----
From: Robert & Linda McGraw K4TAX<mailto:RMcGraw@Blomand.Net>
To: Discussion of Ten-Tec Equipment<mailto:tentec@contesting.com>
Sent: Wednesday, December 28, 2005 10:36 AM
Subject: Re: [TenTec] Mic Extension Cable Doesn't Work
The shield should be connected to pin 2 and the connector shell at the
transceiver end. Based on your description, the shield is floating and is
thus not at system ground potential. Hence, RF getting into the cable and
keeping the PTT circuit in the base of the mike latched on.
In audio, the rule is: Shield is shield and is thus not a current carrier.
Shield should be connected to ground at the load end only. Thus the shield
from the mike to the connector is connected at pin 2 of the female mike
connector which is the same point that a ground wire from the mike is
attached. Then on the extension cable male, pin 2 only has the wire
designated as ground and shield is not connected. Then at the transceiver,
the female cable connector has the ground and shield connected together.
With this method there is a dedicated ground wire from one end to the other
and the shield is connected at one end only.
73
Bob, K4TAX
----- Original Message -----
From: "John Huffman" <hjohnc@adelphia.net<mailto:hjohnc@adelphia.net>>
To: "tentec" <tentec@contesting.com<mailto:tentec@contesting.com>>
Sent: Wednesday, December 28, 2005 7:49 AM
Subject: [TenTec] Mic Extension Cable Doesn't Work
>I have a new Ten Tec 706 microphone that I'm using with my Pegasus. It
>works
> fine, no problems.
>
> The cord is too short, so I bought an extension cable with a 4 pin female
> connector on one end. I wired a 4 pin male to the other end. I connected
> the
> extension cable to the Pegasus and the mike to the other end of the cable.
>
> Audio works fine, but the PPT button and the VOX button on the microphone
> won't
> go off. You have to unplug the mike from the cable to get them to go off.
> I
> start with the buttons off, all is well. I push either button and it locks
> in
> the on position.
>
> I've checked the cable a dozen times. Pin 1 goes to pin 1 and nowhere
> else.
> Same for pins 2, 3, and 4. None of the pins are connected to the shield
> of the
> cable or the shells of the connectors. None of the pins are shorting
> against
> each other.
>
> This even happens when I have the "Xmit Disable" button pushed on the N4PY
> program, so no RF is causing the problem.
>
> I'm guessing it may be a ground problem with the PTT circuit in the base
> of the
> mike. I've tried jumpering the shells at each end of the extension cable
> with
> no luck.
>
> I am at a loss to understand how extending 4 wires would cause the PTT to
> lock
> on.
>
> Any suggestions will be greatly appreciated.
>
> 73 de NA8M
> John
>
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>
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>
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