Loud Squak when i UNkey

[jtrouter]

I have ran into this in the past but have been out of the radio hobby for many years now so i am looking for some help.
I know i have had this problem before with another radio i even think it was one of my tube Robyns? Anyways this time its
with a old Cobra 139 when i unkey the mic i lets out a LOUD squak sound, Its not a squeal but a loud squak. I am using a
4 wire hand power mic. The audio is clean and loud and the radio is stock. The radio is a relay switched radio, Is there a fix
other than a new mic? Hanging a cap or something? Thank you for reading.

 

[Rwb]

I have ran into this in the past but have been out of the radio hobby for many years now so i am looking for some help.
I know i have had this problem before with another radio i even think it was one of my tube Robyns? Anyways this time its
with a old Cobra 139 when i unkey the mic i lets out a LOUD squak sound, Its not a squeal but a loud squak. I am using a
4 wire hand power mic. The audio is clean and loud and the radio is stock. The radio is a relay switched radio, Is there a fix
other than a new mic? Hanging a cap or something? Thank you for reading.

check to see if key is rubbing the hole it moves in. seen a few keys really squeak when keyed. open mic n use small jewlers file n trim a bit n try it again

 

[DoctorAudio]

If it does it with any mic, it may be the switching relay contact timing momentarily isn't unkeying one of the TX circuits before it switches into receive mode or conversely engaging a receive circuit before one of the TX circuits has completely disengaged.
Try popping the lid off of the relay and cleaning the contacts. While you are in there look closely at the contacts with a magnifier to see if any of them are bent or pitted.

 

[jtrouter]

check to see if key is rubbing the hole it moves in. seen a few keys really squeak when keyed. open mic n use small jewlers file n trim a bit n try it again

Thanks for the reply but its not a rub, Its a electronic LOUD noise more like a Browning ping or whatever you want to call that sound. its high pitched and so loud i get worried when i use the radio at night im going to wake the house.

 

[jtrouter]

If it does it with any mic, it may be the switching relay contact timing momentarily isn't unkeying one of the TX circuits before it switches into receive mode or conversely engaging a receive circuit before one of the TX circuits has completely disengaged.
Try popping the lid off of the relay and cleaning the contacts. While you are in there look closely at the contacts with a magnifier to see if any of them are bent or pitted.

This is what ive been thinking it is, I also remember reading something about Mics that have 6 odd wires use a different key system unlike the normal 4 wire mics that i have a box full of. I know i used to have this problem using D104's on old radios.

 

[Handy Andy]

This is what ive been thinking it is, I also remember reading something about Mics that have 6 odd wires use a different key system unlike the normal 4 wire mics that i have a box full of. I know i used to have this problem using D104's on old radios.

and...

Because of a potential lag in the relay, your mic switch contacts may beat the relays contacts to the punch by striking ground first - causing this "pop" condition.

Any way you can set up the mic to be Electronic Switching"? Then you don't force the mics ground TX/RX switch contacts to ground first causing the speaker to connect quicker than the relay can switch over?

Try leaving Pin 4 on the MIC handset disconnected and let the relay switch over instead.

Now, before I get jumped on,

Pin 4 is part of the shield - being that the Mic Pin 4 is connected to SHIELD the wire in the harness to the Handset.

At the Handset - review the switch - Pin 4 wire that normally grounds the SPEAKER (typical later model Cobra Uniden 4-pin) - just leave it open - so the ground and Pin 3 are not fighting each other for contention at Pin 1 and Pin 4 - leave the mess at Pin 1.

Got and Owners manual? Look at Pages 17 and 18...
​

Then when you do this - PIN 1 Shield (Braid) needs to be in the CENTER contact of the DPDT (Or the common to one pole - being ground of the switch) at all times

Considering how old the radio is, this step may already be done by the factory, but its age is letting you know it might need a once-or-twice go-over to replace some caps to restore the RX/TX switching speed.

This is why...

 

[jtrouter]

and...

Because of a potential lag in the relay, your mic switch contacts may beat the relays contacts to the punch by striking ground first - causing this "pop" condition.

Any way you can set up the mic to be Electronic Switching"? Then you don't force the mics ground TX/RX switch contacts to ground first causing the speaker to connect quicker than the relay can switch over?

Try leaving Pin 4 on the MIC handset disconnected and let the relay switch over instead.

Now, before I get jumped on,

Pin 4 is part of the shield - being that the Mic Pin 4 is connected to SHIELD the wire in the harness to the Handset.

At the Handset - review the switch - Pin 4 wire that normally grounds the SPEAKER (typical later model Cobra Uniden 4-pin) - just leave it open - so the ground and Pin 3 are not fighting each other for contention at Pin 1 and Pin 4 - leave the mess at Pin 1.

Got and Owners manual? Look at Pages 17 and 18...
View attachment 56898​

Then when you do this - PIN 1 Shield (Braid) needs to be in the CENTER contact of the DPDT (Or the common to one pole - being ground of the switch) at all times

Considering how old the radio is, this step may already be done by the factory, but its age is letting you know it might need a once-or-twice go-over to replace some caps to restore the RX/TX switching speed.

This is why...
View attachment 56899

Thank you VERY much for the detailed thoughts. I will check into those today and report back.