| Author |
Message |
    
Chad
Intermediate Member
Username: Chad
Post Number: 331
Registered: 11-2004
| | Posted on Monday, June 20, 2005 - 2:22 pm: | 
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At a yard sale the other day and found a Cobra 29LTD Classic, new, in the box, wrapped, no fingerprints but mine. Bought it for 25 bucks.
Put it in the truck and found that if I use my Wilson trucker mic that the dynamike acts like a talkback. Stock mic works fine. Wilson works fine in the house on the DX2547.
I was on chat with lon, Tech291 and others before I tried the stock mic, thanks for your time guys, I feel like a fool by swearing it had talkback and wanting to disable it 
I really like the wilson trucker, it's noise canceling and I have a pretty deep voice, this mic seems to have a mid boost in the right spot for me. Not to mentiopn the stock mic is...well....not so great.
I wanna use the wilson. I checked the connectoer wiring and it's right. The mic has a very low impedance element going to a transformer to raise the impedance and this is then cap coupled to the input of the radio via a .1uF cap Could be .01? pretty sure .1 though.
What gives? This is the craziest thing I have seen in a while!
Chad |
Bc910
Advanced Member
Username: Bc910
Post Number: 543
Registered: 7-2004
| | Posted on Tuesday, June 21, 2005 - 1:15 am: |
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Chad
Simply put,
The Cobra uses a 4 wire/4 pin plug
Most exports use 3 wire/4 pin.
On the cobras and unidens, etc there is a "recieve" wire without which you get no audio on your recieve. This is why when you unplug the mic the audio drops to next to nothing. Most exports don't have this "recieve" wire there for when the mic is unplugged the recieve doesn't drop.
When you cross your recieve wire with your shield on a Cobra BAM you get talk back! The mic gain was doing as it should, adjusting mic gain. On the export since there is no "recieve" wire this isn't a problem.
Simple solution:
check the wiring of the mic, it should be
Pin1=Shield
Pin2=Audio
Pin3=Transmit
Pin4=Receive
obviousely pin 1 and 4 are crossing somewhere, either at the plug or in the mic or at the key.
Hope this helped, I know i said at the begginning "simply put" and it wasn't but... hope you get the idea
BC |
Hollowpoint445
Intermediate Member
Username: Hollowpoint445
Post Number: 424
Registered: 6-2004
| | Posted on Tuesday, June 21, 2005 - 6:39 am: |
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I've never owned either that microphone or that radio, but I'd have to guess that the microphone isn't wired correctly. It sounds like the radio isn't properly switched from receive to transmit and the audio is making it's way to the speaker during a transmission.
If you feel like experimenting - connect only the ground and audio from the microphone and use a clip lead to switch the radio into transmit mode. If it doesn't happen then I'd say it's definitely the switch wiring. If it does then I've got no clue without poking around in the microphone.
Nice deal by the way! |
Chad
Intermediate Member
Username: Chad
Post Number: 333
Registered: 11-2004
| | Posted on Tuesday, June 21, 2005 - 8:42 am: |
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Cool! Should have the new car back from the body shop today so the truck can go to the barn for a while. I'll grab the cobra out and try playing with the mic wiring a bit. It just blew my mind (and my ears! cranked the dynamike and keyed up, SHAZAM!)
I compared the stock mic to the wilson with a meter and all was the same except the lack of resistance on the wilson on the audio send (cap coupled). I'll tinker around and let you all know what I find!
Chad |
Chad
Intermediate Member
Username: Chad
Post Number: 334
Registered: 11-2004
| | Posted on Tuesday, June 21, 2005 - 8:44 am: |
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BC, If I read it right you feel that on transmit I have BOTH pins 3 AND 4 grounded? This could be. I'll check that out!
Guess it's a darn easy talkback mod if someone wants it I hate it!
Chad |
Hollowpoint445
Intermediate Member
Username: Hollowpoint445
Post Number: 425
Registered: 6-2004
| | Posted on Tuesday, June 21, 2005 - 4:26 pm: |
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Nope - The RX pin should not be grounded when you are transmitting. That's the problem. |
Bigbob
Senior Member
Username: Bigbob
Post Number: 1999
Registered: 12-2001
| | Posted on Tuesday, June 21, 2005 - 9:28 pm: |
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You know what?My buddy had this problem and his mike cable was too long,huh?Yep,RF from his rear mounted antenna was being rectified in his mike cable,cut the cable from 7 feet to 4 feet and no more talk-back,that sucked so we got another long cable and decoupled the audio and shield with .01mfd ceramic disc caps,much better solution |
Coyote
Intermediate Member
Username: Coyote
Post Number: 248
Registered: 11-2004
| | Posted on Tuesday, June 21, 2005 - 11:28 pm: |
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Gotta love them yard sale deals! Good find Chad. |
Chad
Intermediate Member
Username: Chad
Post Number: 337
Registered: 11-2004
| | Posted on Wednesday, June 22, 2005 - 8:33 am: |
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Thanks. I really like the radio. I've been into the more techno-type radios lately like the 257 etc. This is just a no frills AM unit with good audio that has the features I needed. I spend most of my time on sideband DX ing but found it to be a waste in the truck. The 257 is MUCH better suited tied up to the Imax!
Chad |
