Cobra 142 GTL making popping sound when microphone key is released fast.

[snippits75]

Using a Cobra 142 GTL with a D104 hand held power mic, and have headphones connected to external speaker jack. Radio is stock, and nothing has been clipped or volted. When I release the mic key fast like I do normally, I hear a loud pop. Release the mic key slowly, and it does not make a popping sound.

A friend of mine said his Cobra 2000 does the same thing, but releasing the mic key slowly, and there is no popping sound coming through to the headphones.

Is there a common fix for this problem?

 

[nomadradio]

Is there a common fix for this problem?

Yep. Release the mike slowly.

The hand mike has a switch that opens the transmit side, causing the "POP" before closing the speaker circuit. This short delay prevents the pop from being heard.

Doesn't take much, around 1/30th of a second more or less.

We developed a conversion gadget for the Uniden-made sideband CB radios with the 5-pin mike socket. Converting it to 4 pins requires a relay to keep the radio's two separate ground circuits separate from each other. Put it all on a small printed circuit board soldered to the back of a 4-pin mike socket.

This caused the "POP!" problem because the relay turned on the speaker too fast when you unkey. Ended up redesigning it to use two relays. One relay for the transmit side, and a second one that had a short delay before turning the receiver speaker back on. Cured the POP problem, but made the whole thing hard to fit on a sufficiently-small circuit board.

The spring contacts in the switch can become distorted if someone tries to "adjust" them instead of just cleaning out the oxide schmoo. This can disrupt the timing, causing the speaker to be turned back on too soon.

Maybe fiddling with the leaf contacts in the mike will help.

Might make it worse.

73

 

[snippits75]

Thank you Nomad!

I don't have another five pin mic to play around with right now. Got a five to four pin adapter on order, so I can try the other four pin microphones I own, and see if I get the popping sound with them.

Have a four pin D104 hand held too, and I will try that one to see if it pops like the D104 hand held five pin.

Until then, release the mic key slowly!

 

[nomadradio]

The use of a 4-pin mike on the 5-pin SSB radios like that one presents you with a math problem. Five doesn't equal four.

The five-pin socket has two separate ground pins. Pin 2 carries only the ground current for the mike's audio signal. Pin 4 carries only the circuit currents for the speaker on receive, and for the transmit-switch circuit when you key the mike.

An adapter will be wired one of three possible ways. With only pin 2 connected, or only pin 4 connected, or with a jumper connected to both, where the 4-pin mike's one and only ground wire will connect.

One setup tends to cause feedback squeal in transmit. The other mainly in SSB receive mode, and the other one balances the squeal noises between both.

This is one of those "my buddy Joe got away with this" propositions. Might work okay. Might not. If it's just your radio, why not try it?

But it someone is paying you to fix up a radio that won't make squeal noises, it's better to stick with a "for sure" setup than a "it might" setup.

And if the adapter doesn't work out the way you want, there wasn't a lot wasted to find out.

73

 

[johnnytek]

Using a Cobra 142 GTL with a D104 hand held power mic, and have headphones connected to external speaker jack. Radio is stock, and nothing has been clipped or volted. When I release the mic key fast like I do normally, I hear a loud pop. Release the mic key slowly, and it does not make a popping sound.

A friend of mine said his Cobra 2000 does the same thing, but releasing the mic key slowly, and there is no popping sound coming through to the headphones.

Is there a common fix for this problem?

bend the contacts in the mic to release the audio 1rst