Clean transmission, but often messy reception

[jdmason]

Hi All,

I currently have an issue that I am trying to solve. When I talk through my CB mic, all my friends (and other nearby drivers) can hear me perfectly. However, when they try to talk to me, I often just hear loud static mess. Sometimes I can hear them crystal clear, so I know it isn't a blown speaker. Other times, however, as soon as they try and talk it's just a loud screechy static mess.

What might be causing this intermittent issue? It happens regardless of my squelch or RF gain settings. I am using a Uniden 520XL unit. The unit receives power directly from the battery, through a 15A fuse (as well as it's own inline glass fuse) in an aux. fuse box. The CB antenna is mounted to my tire carrier on the back of the vehicle, which is made from steel and painted in bed-liner.

Please let me know if you have any ideas/suggestions.

Thanks!

 

[wtp]

two ideas

try turning the rf gain wayyy down and see what happens, even to 0
as you hear someone talking to you try going up and/or down a channel or even two.

 

[Oldme]

Because you said regardless of RF Gain setting or Squelch and you
added if is sometimes a static mess, I would be thinking a cold
solder joint on the audio side or other bad internal connection.

Could be as simple as a speaker wire.
Have you tried it with an external speaker?
If it is the speaker wire and external speaker would bye-pass it.

 

[SpectreOZ]

Agreed, you may be experiencing receiver overload....

 

[JayMojave]

Good advice here. Trying a external or another speaker would be a good call to reinforce its not the speaker.

Like OldCB Said it could be a cold solder joint or intermittent connection. A audio signal tracer can be used to trace and identify the circuit causing the problem. Taking a guess at this I'd say some sort of connection, oscillation, bias or capacitor problem is causing all this. A bias problem will always cause a distortion problem. Good luck, please let us know what you find.

Jay in the Mojave

 

[jdmason]

Good advice here. Trying a external or another speaker would be a good call to reinforce its not the speaker.

Like OldCB Said it could be a cold solder joint or intermittent connection. A audio signal tracer can be used to trace and identify the circuit causing the problem. Taking a guess at this I'd say some sort of connection, oscillation, bias or capacitor problem is causing all this. A bias problem will always cause a distortion problem. Good luck, please let us know what you find.

Jay in the Mojave

Ok, so step one is to use an external speaker. I will go get one and test it out.

If that doesn't fix it, how exactly do I trace the signal within the unit? I am assuming I have to take the unit apart and test each circuit individually? I am not overly experienced with this sort of thing, so any advice would be of great help! I will keep you all posted!

 

[Oldme]

if trying an extremal speaker and it does not indicate that is
the problem then you have to feel very comfortable
opening the unit and working on a unit when it is turned
on and hooked up to the antenna.

While Lightly pressing on the board with the unit on with a
non-conductive (wood or plastic stick) around each component
while listening for a change in what you hear.

If you find a change then the fix is soldering (re-flowing the existing solder).
If you have no experience soldering a circuit board, then you need a tech.

Tracing circuits will require equipment you most likely do not have.

Best advise is if it is not a simple speaker wire loose, take to a
tech to be checked.

 

[jdmason]

I should note that sometimes even with RF gain all the way down, and squelch down as well, I still get some pretty nasty interference noise. I still have yet to get myself an external speaker, but I am wondering if this might have something to do with my antenna as well?

How can I ensure my antenna is properly isolated and/or grounded? I know they're supposed to be grounded, but it confuses me how because I also know that the plastic washer that comes with my antenna is to isolate it from my metal mount.

Any advice?

 

[Oldme]

If you were having a grounding problem with the antenna you SWR would be way off.
Have you used a separate meter to check it? The factory meters are usually only "close".

If you have an electrical ground problem to your radio, your radio would cut on/off.

Have you opened the radio and looked at the connecting wires to the speaker on the inside?
Make sure the wires have a solid connection.

You are now using the word "interference" - before you indicated a scratchy audio.
Two Different things.
Interference with the radio would be coming most likely from an outside source.
Transformers near by, certain types of lights, electric motors running, etc.
These would be a hum or buzzing sound.
A wining sound would be the alternator, Popping sounds - the spark plug wires.
Certain headlights add noise sometimes.

 

[jdmason]

If you were having a grounding problem with the antenna you SWR would be way off.
Have you used a separate meter to check it? The factory meters are usually only "close".

If you have an electrical ground problem to your radio, your radio would cut on/off.

Have you opened the radio and looked at the connecting wires to the speaker on the inside?
Make sure the wires have a solid connection.

You are now using the word "interference" - before you indicated a scratchy audio.
Two Different things.
Interference with the radio would be coming most likely from an outside source.
Transformers near by, certain types of lights, electric motors running, etc.
These would be a hum or buzzing sound.
A wining sound would be the alternator, Popping sounds - the spark plug wires.
Certain headlights add noise sometimes.

Valuable things to know, thank you.

Yes, I should say that it isn't just a scratchy sound. Sometimes I get screeching/humming/buzzing when nobody is talking, although that is less common.

More often than not it occurs when people try to talk to me. Everything is perfectly quiet, and then I key in the mic to say something. They all report that they can hear me perfectly fine, however as soon as they key in their mics all i can hear on my end is loud screeching, sometimes with a faint hint of what they are saying. That happens about 70% of the time. The other 30% of the time I can hear them crystal clear, like nothing is wrong.

This happens wherever I am, regardless of whether I am in the city or on an open country road.

 

[jonwienke]

How can I ensure my antenna is properly isolated and/or grounded? I know they're supposed to be grounded, but it confuses me how because I also know that the plastic washer that comes with my antenna is to isolate it from my metal mount.

Any advice?

The coax shield needs to be grounded to the body of the vehicle, but the center conductor needs to be insulated from the body, or you're shorting out your signal. The plastic washer insulates the antenna mounting stud (connected to coax center) from the ground.

 

[Oldme]

The plastic washer insulates the CENTER WIRE which carries the signal.

The beaded shield part of the coax is what is grounded.

The connection for the beaded shield is made to ground either by
the Pl259 connector (usually at the radio on a mobile)
the internal connection on a magnet mount (you may not see that) pre-made
or to the antenna mount/bracket. It is usually stripped back, twisted and a wire lug
that goes between the bracket and the antenna connector stud nut makes the
ground connection. All should be tight.

The antenna mount should be tight, bare metal to bare metal is best.
I used several mounting screws and a finder bolt on my finder mount.
to get the best ground I could.

If the center wire is broken at the antenna connector stud you will have
a problem on receive and transmit (cuts on/off).

Check for corrosion where the antenna screws on.

 

[iMONITOR]

Most CB'ers equipment is over powered, over modulated, and have so many kitchen-table mods and hacks, it's amazing you can understand them at all.

The best "sounding" CB's are usually stock.

 

[jim202]

Most CB'ers equipment is over powered, over modulated, and have so many kitchen-table mods and hacks, it's amazing you can understand them at all.

The best "sounding" CB's are usually stock.

It's possible your receiver is off frequency. Another thing I would try is to listen to another channel and see what other conversations sound like.

Need a base line here to figure out which way to point the finger. If you take your friends out of the picture and try to listen to others just talking away, it will let you know if it's your radio receiver, over modulation from your friends, or if your speaker is bad.

Jim

 

[Oldme]

Most CB'ers equipment is over powered, over modulated, and have so many kitchen-table mods and hacks, it's amazing you can understand them at all.

The best "sounding" CB's are usually stock.

Some - yes

Most - NO.

Blanket statements never work.

There does seem to be a trend, "now" vs "back in the day" for over modulation.
Way back when, clean was important.

Stock can be clean depending on quality control.
Most will come off the assembly line with less than the 4 watt limit and
only about 50% modulation. That leads to the problem of trying to get
to the legal limit and increasing modulation without creating problems.

Many CB centers, not just kitchen tables, think you need to spread coils
and clip limiters. Both are sure fire ways to sound horrible.

I watched a "real genius" on u-tube tell everyone to adjust a certain
point for more power. He showed his meter to prove it.

What he did and did not know it, was readjusted his meter!
He was not putting out any more power, just the improperly
calibrated meter showed more.

 

[iMONITOR]

Some - yes

Most - NO.

Blanket statements never work.

You're probably right. However, living in the Detroit Metropolitan Area, "Most" would apply! :wink:

 

[Oldme]

I am not sure which is worse.
Having nothing but mud ducks all around like you have
or having next to no traffic like I have around here near Athens Ga.

There are a couple on the air now and then, that I wish would put their teeth in
when they talk.

I sure miss the "old days".

 

[Oldme]

Valuable things to know, thank you.

Yes, I should say that it isn't just a scratchy sound. Sometimes I get screeching/humming/buzzing when nobody is talking, although that is less common.

More often than not it occurs when people try to talk to me. Everything is perfectly quiet, and then I key in the mic to say something. They all report that they can hear me perfectly fine, however as soon as they key in their mics all i can hear on my end is loud screeching, sometimes with a faint hint of what they are saying. That happens about 70% of the time. The other 30% of the time I can hear them crystal clear, like nothing is wrong.

This happens wherever I am, regardless of whether I am in the city or on an open country road.

With the additional information you have just given
I would be looking either a mike that is not releasing
the transmit relay or a misalignment of the receive section.
A tech is needed that can checkout the circuits.

 

[JayMojave]

Hello jdmason: Trouble shooting over a forum isn't real easy. If you figure your problem isn't the speaker, or mic cord and such. Or local near by interference from some other station.

Using a "Signal Tracer" to find the bad stage in the receiver is usually done by a Tech, as they are the ones that have a old piece of test equipment like that. The Signal Tracer is a audio amplifier with a diode, capacitor, and resistor in the pick up probe to protect and detect the radio signal in a receiver. There are many web sites showing this. The Signal Tracer simply allows you to listen to the signal at the different stages of the receiver allowing you to isolate the stage or circuit that is bad.

I don't know if new Signal Tracers are made and sold, but there will listed on E-Bay or Amazon. Its a older piece of test equipment not very well appreciated or given the credit it deserves.

I am no radio bench Tech that works on radios day in, day out, but I have isolated then repaired a few radios using a Signal Tracer and a Volt Meter. Looking at the radio schematic will show you a Tech where to monitor and place the input probe of the Signal Tracer, again allowing you hear the signal of that stage. Good Luck.

Jay in the Great Mojave Desert

 

[com501]

The Uniden 520XL is a less than $50 CB radio. If you bring it to me to be checked, the charge is $45. I will simply hand you a new one in the box. You should do the same. It is simply not worth the effort.

Make sure your antenna mount is good and call it a day. Use the old radio for skeet practice.