astatic kills my white noise and volume

[johnecashflo]

i had a stock mic on a cobra 29..had to barely crack the volume to hear the rx. audio..hooked an astatic 636 and i have to double the volume to here the rx audio..is this an astatic thing ?? i tried it (astatic)on another cobra and it does the same thing..

 

[loosecannon]

might have a bad connection to the receive wire in the mic plug.

sometimes if you turn the volume all the way up, you can hear some faint noise through the speaker, with no mic connected.
you might be mistaking that phenomenon for this symptom.

try resoldering the connections on the astatic's plug, and also make sure its wired right.
here is a link to a page with all kinds of info for your cobra 29.
including the mic wiring for whichever type of astatic mic you have.

http://www.cbtricks.com/radios/cobra/29ltd_29ltd_st_29wx_st/index.htm

the pin numbers are stamped on the little black plug, you just have to look real close.

want an easy method to make sure its the mic and not the radio?
have a voltmeter handy?

set the voltmeter to read continuity. (so that when you touch the leads together the meter shows a direct short)

now unplug the mic from the radio, remove the power cord from the back, and any other connections such as antenna, or an external speaker.

take off the bottom cover of the radio, (the one with the speaker on it)
and set the radio down on the edge of it so that you can leave the speaker connected. (have the radio upside down so you can see the components. the bottom cover should be on its side with the weight of the radio holding it up)
can you picture it?

now, put one lead of your voltmeter on any one of the metal tuning cans that you see in the radio, (you know, the ones we're not supposed to touch).
the metal chassis of the radio will not work.

now, while holding one lead on a tuning can, touch the other lead to each mic pin on the connector until you see the meter move or however the voltmeter reads a direct short.

you have found your ground pin.
draw a picture of the connector on the radio and label this pin.

now hook the radio back up, but leave the mic off.
turn it on, and using a short length of wire as a jumper; touch one end of the jumper to the ground pin, and the other end to each of the other pins.

one pin will cause the radio to go into transmit mode.
that is your TX pin.

one pin will cause the receiver audio to be heard.
that is your RX pin.

and one pin might scare the crap out of you by making a loud BOOOP! sound when you touch it.
that is your audio pin.

there ya go.

sorry if you already know all this stuff, i like to type it out so that in the future, someone might find this thread helpful.
later,
LC

 

[johnecashflo]

thanks for the info LC..the problem is as you stated when the astatic mic is pluged in i can hear fine its just that i have to turn the volume knob up twice as much to here the same db. as with stock mic or RK56..the mic works fine on 10 meter radio

 

[loosecannon]

well, im confused then.

all a microphone is, is a switch and a mic element.
there is nothing there to attenuate the receive of the radio.
the switch is either connected or it isnt.

if the jumper method causes the radio to receive normally, and the astatic mic when plugged in, causes the receive to be half as loud as with the jumper method; then there is something very strange going on with that mic.

has it been messed with by anyone?
im really stretching here, but did someone try to install a resistor in the mic audio line to cure feedback, and accidentally wire it to the receive wire, or ground wire?
im not even sure if that would cause the symptom you are having.


i hope i dont sound condescending, because im not, but it really sounds to me
like the mic is wired wrong or has a bad connection, and you hear the receive audio that exists even when no mic is plugged in.

so, with no mic on the radio, turn the volume all the way up.
does it sound like it does when the astatic is plugged in?

we are talking about a cobra 29ltd here right?

check the solder connections on the plug of the astatic mic.
LC

 

[sidewinder202]

astatic mic

make sure the blue and sheild are together otherwise that would probably happen a simple fix

 

[W5LZ]

LC,
Don't ask me why cuz I have no idea. But, with some CB radios if you unplug the mic you loose all receiving audio. Has to do with some switching done in the microphone. Doesn't make any sense to me, but 'they' didn't ask me so that's how it's done.
- 'Doc

 

[Captain Kilowatt]

LC,
Don't ask me why cuz I have no idea. But, with some CB radios if you unplug the mic you loose all receiving audio. Has to do with some switching done in the microphone. Doesn't make any sense to me, but 'they' didn't ask me so that's how it's done.
- 'Doc

Doc, that's because the PTT switch is wired as a SPDT with ground being common. One side of the switch is connected to the RX and the other connected to the TX side. Each has a transistor switch to enable the Tx/Rx function.The transistor is turned on when the ground is applied thru the switch.The old relay switched sets did the same thing except the relay used the N.C. contacts for the RX.Another design "improvement".

 

[9C1Driver]

You guys have the problem pinned down for him. The reason the mic works fine in an Export radio is they are different. When you unplug the mic on an export the receive stays there, on a cb set you loose your receive. Get the mic wired up correctly and it will work fine for you.

 

[HiDef]

I dunno what lives inside a Cobra 29 but some sets don't fully switch the audio input which is common to receive and transmit all by themselves. They also use some contacts inside the mic. Some Astatic mics short out the audio lead on receive. This combination could be the problem.

 

[sidewinder202]

mic wiring

this should work fine for you on either cobra or export radio ,,,pin 1 ground and blue together ,,pin 2 white,,,pin 3 red,,,,pin 4 black yellow no conection at all that should cover cobra , uniden , most all 4 pin exports hope this helped