cb radio feedback

[blue beasty]

The internal speaker on me cb is duff so got a little battery powered plug in jobbie which works great apart from it screeches horribly when I transmit. Thought it might be because it was right next to the cb so got an extension cable for it but doesn't make any difference whether it's 2" or 5' away.

Doesn't make any difference if the engines running or not or even if the ignition is on (got it wire to my aux battery)

It works ok but is just horribly irritating

Anyone got any bright ideas

 

[Funkykipper]

I've got the same with mine but more permanent noise. Be interesting to see the feedback so basically ....

:nothingtoadd:

 

[Drookit Dug]

When you transmit your speaker plays what you are saying, this is picked up by the mike which sends it to the aerial via the amp. This is played through the speaker which is picked up by the mike.
This cycle goes on many times a second and each time it is amplified a bit more until it becomes the noise you describe

 

[Drookit Dug]

And yes FK. It is called feedback as it is fed back to the amp and reamplified every time.

The internal speaker will be inhibited during transmit. As soon as you key the mike the internal speaker is automatically muted unless it has a 'sidetone' facility so you can hear what you are saying but this prevents feedback

 

[blue beasty]

When you transmit your speaker plays what you are saying, this is picked up by the mike which sends it to the aerial via the amp. This is played through the speaker which is picked up by the mike.
This cycle goes on many times a second and each time it is amplified a bit more until it becomes the noise you describe

Don't think so......it does it just pressing the transmit button and everything is quiet

 

[Drookit Dug]

The same thing happens with hearing aids if you hold them in a closed fist! It hears a noise and amplifies it, it then hears the amplified noise and amplifies it again and again until all you can hear from your fist is a squeal!

 

[Ltwt Hybrid 300tdi]

Hello,does the CB have a female jack plug socket for an external speaker (ext)? If it has one marked PA this is for the public address system (for telling the neighbourhood never to vote Tory again!)

 

[blue beasty]

Hello,does the CB have a female jack plug socket for an external speaker (ext)? If it has one marked PA this is for the public address system (for telling the neighbourhood never to vote Tory again!)

OOOoooooo never thought of that :doh:......I'll check in the morning

Good thinking

 

[Drookit Dug]

You might think its quiet but the amp hears everything and feeds it back

 

[easye1]

just change the speaker inside the cb.
propa job.


quick question.

when out off roading or laning, do you use the old naughty 40`s or fm euro/ fm uk 40..?

its just a question, so dont respond if its a "not quite right" answer eh..

Its just that I have all 3 sorts of cb`s hanging around for years...

 

[Funkykipper]

Think it's FM UK that we use. Definitely not EU.

 

[easye1]

Think it's FM UK that we use. Definitely not EU.

thanks.

 

[easye1]

I've got the same with mine but more permanent noise. Be interesting to see the feedback so basically ....

:nothingtoadd:

is the cb wired through the ignition?
or via the battery?

if through ignition, you may be picking up "noise" that way.

 

[Funkykipper]

is the cb wired through the ignition?
or via the battery?

if through ignition, you may be picking up "noise" that way.

Earth to the body and power straight to the battery. The springer is attached to the light bar in the centre.

 

[Clanforbes]

Sorry, drookit, but feedback in this form is purely audio being picked up by the mic and "looping" back through the audio amp causing the amp to go into overdrive ... the aerial doesn't figure in the equation at all.

The symptoms the OP describes is most likely caused by one of three faults.

1. The TX switching transister is not doing it's job properly and allowing the RX circuit to stay active during TX.

2. The contacts in the microphone are not breaking the audio output properly (when the GND wire switches to the RX position in the PTT switch this activates the speaker whether external or internal and likewise disconnects the speaker when the PTT button is pressed.)

3. There is a bad connection somewhere in the rig (dry joints are very common) or possibly a short in the mic cable.

Open the back of the mic and check that the wires are not frayed, also check that all the soldering is nice and neat. Check the same at the plug end also. A damn good squoosh of WD40 into the slider of the PTT button, whilst pressing it in and out, often cures problems related to the PTT switch (crackling, noisy audio, audio that sounds like you are in a wind tunnel etc.)

As for it being because the speaker is plugged into the PA socket, this is very unlikely as most rigs would require the user to switch the unit into PA mode before the PA speaker will kick in.... But sometimes in older rigs the PA/CB switch can get grotty (WD40 will cure that also.)

The rig (guessing from the fault described) sounds like it is an old DNT or possibly a YORK. But further guesses would be useless as no one has mentioned the make or model of the units involved, I very much doubt it'll be an Amstrad 901, or a Audioline. Most likely it'll be a cybernet chassis based rig. (The little old midland 99's and 104's did this occasionally also.)

Hope this helps.