Cobra 29

1096 · Post by **1096** » Friday 12th Sep 2008, 12:02

I am having an issue with a squeak heard through the talkback but it is not being transmitted and the speaker is not close ( not feedback from too loud of a talkback ).... The radio is a 29 nw st with an IRF520 for a final.... I have tried the ERF2030 too and it does the same thing.... Power output is fine but it squeaks as you key up very quickly.... Tried everything from grounds to changing the mic jack.... The noise is being generated as the PTT is being pressed.... It's pretty loud and I have literally done 100 of these with out one single issue like this.... I am at wits end with this thing.... Could this be an issue with the soundtracker circuit.... Any ideas???

ramblingman · Post by **ramblingman** » Friday 12th Sep 2008, 12:23

Disconnect the small disc capacitor that is connected to the
base tab of the audio chip.And see if it still does it.Also if this
does not help.Try installing a rf bead on the audio lead at the mic
socket.Also try installing a 0.1 uf disc cap. from the audio wire
at the mic socket to the shield wire.Also what type mic are you
using on the radio.

1096 · Post by **1096** » Friday 12th Sep 2008, 12:36

I'm using a Road King 56 on it because that is what this person intends to use with it also.... I ran a 1k resistor in series with the audio line and nothing hapened and I also removed the cap at the audio chip and nothing either.... The radio did have a resistor soldered across the receive pin that went to the shield.... I removed that resistor but don't know if the noise started before or after I removed that....

ramblingman · Post by **ramblingman** » Saturday 13th Sep 2008, 10:25

Yes your are going to have to have that resistor in line
with the rx wire.What this does is shunt any rf back to
ground.To keep it out of the rx circuit.That is probably
why you are getting squeal at keyup.