Unkey TX speaker pop

[darklife]

Hi all.

I have a Teaberry Five-by-Five that I have been playing with for some time and there is one thing about it that annoys the heck out of me.
When I unkey with the stock mic quickly there is a light pop sound in the speaker upon going back to receive.
When releasing the PTT button slower at a normal pace there is no pop.
This would be fine but I want to use my desk mic and it has a PTT switch that releases quickly between internal switch contacts causing a loud pop in the radio.
It is almost like the radio expects some dead space between the PTT switch contacts between making contact from TX to RX.

I know for a fact that it is not the mics but the design of the radio itself. I read a while back that a few radios like this had the same issue.
I am wondering what causes it and if there is any fix?
It has to be something with the electrical RX/TX switching in the radio itself, maybe even by design to cheapen it somehow.

Also I notice there are no schematics on the web for this radio. The few sites that have a PDF I click to download but it is the wrong diagram.

Thanks for any ideas.

 

[Beetle]

Try putting a microfarad or two of capacitance across the speaker terminals. Not electrolytic. I used to do this back in the days of separate transmitter and receiver and it quieted my speaker just fine.

Experiment with the amount of capacitance. If you have access to a capacitor substitution box, you can save a lot of time. Otherwise, alligator clips do well in this.

 

[midnight special]

dosent the 5x5 have mechanical relays? if they do they might need cleaning and lubrication.......

 

[darklife]

dosent the 5x5 have mechanical relays? if they do they might need cleaning and lubrication.......

No relay inside.

 

[loosecannon]

is this your radio?

Teaberry Five by Five

if so, take a look at the schematic.

you most certainly do have a relay in there, look just to the right of the mike symbol and you will see the coil of the relay. the contacts are spread throughout the schematic.

LC

 

[darklife]

is this your radio?

Teaberry Five by Five

if so, take a look at the schematic.

you most certainly do have a relay in there, look just to the right of the mike symbol and you will see the coil of the relay. the contacts are spread throughout the schematic.

LC

As I said above that schematic is the wrong schematic. They say it is the schematic for the Five by Five but it is actually for a different (older) model that uses a relay.
That is the site I tried to get a schematic from and it is the wrong one listed in the link.
Funny thing is the service manual on the site is mostly correct for my radio but once again is for a different radio. I should probably contact the site owner and let them know this.

There is absolutely no relay inside my radio. I know my way around schematics, build my own electronics from scratch and so on so you can trust that I know what schematic belongs to my radio and if it has a relay or not in it :tongue:

I traced most of the important parts of the radios printed board to paper and hand drawn a schematic and all the PTT switching is done by diodes in the circuit.

 

[darklife]

Here is my radio for confirmation...

As you can see no relay besides the blue one on a roger beep I added. You can also see the extra unlabeled switch in the previous photo which switches roger on/off, however keep in mind that the speaker pop issue existed before this mod even with the stock mic...

One last thing.. I love the champaign coloring of this radio. The pic really doesn't give it credit. I just wish the underside was not scratched up, otherwise it is a beauty for a 23 (added channel 24 in the blank space on the dial radio) channel radio.

I plan on adding a crystal switch in the future to get some extra channels much like I did with the roger beep switch. These uniden "teaberry" radios has lots of unused slots behind the faceplate for switches and I have a carcass of an old radio with identical switches I can put in where the empty spaces are

 

[darklife]

One thing I found that helps so far is putting a low ohm resistor in parallel with the speaker wires to force quiet the speaker and then crank up the CBs volume to accommodate.
This reduces the pop greatly but obviously is kind of dumb since I have to turn up the radio now to get the same volume.
I will try a capacitor in parallel next as Beetle suggested. Problem is that I lose the high frequency audio reproduction. I am kind of into HIFI AM CB stuff so this may be a nasty trade off if it works.
Then there is external speaker which once again brings the problem back.

What ticks me off is this radio was designed like this. I feel like I need to re engineer the radio to solve it, but that is fine because I want to hotrod this POS lol.

 

[Robb]

Where's Waldo?

That is an add-on board with a relay and your 'pop' source.

 

[Shockwave]

Robb is right. Without a doubt the source of this pop was introduced upon installation of the roger beep. Just about every radio that receives without a mic plugged in will pop like you described. That radio use to need a mic to receive but once you added the roger beep, the relay took over the receive control. Relays are too fast without proper sequencing to eliminate the switching transients between transmit and receive.

Modern radios also have these switching transients however, you do not hear them because the receive wire in the mic is the last connection made when you release the button to connect the speaker. By then enough time has passed so the pop has already occurred before the speaker is connected.

Tram D-201 radios are noted for this problem and I've fixed many just by using the extra pin in the mic plug as a receive control from the mic to connect the speaker inside the radio. Unless you slide your finger off the key switch instantly, you can't release the button fast enough to make the pop.

 

[darklife]

Robb is right. Without a doubt the source of this pop was introduced upon installation of the roger beep. Just about every radio that receives without a mic plugged in will pop like you described. That radio use to need a mic to receive but once you added the roger beep, the relay took over the receive control. Relays are too fast without proper sequencing to eliminate the switching transients between transmit and receive.

Modern radios also have these switching transients however, you do not hear them because the receive wire in the mic is the last connection made when you release the button to connect the speaker. By then enough time has passed so the pop has already occurred before the speaker is connected.

Tram D-201 radios are noted for this problem and I've fixed many just by using the extra pin in the mic plug as a receive control from the mic to connect the speaker inside the radio. Unless you slide your finger off the key switch instantly, you can't release the button fast enough to make the pop.

That may be, but once again as I said before the problem existed BEFORE I installed the homebrew roger beep which makes me wish I had not even mentioned it because it just adds confusion.
You are absolutely right about the switching transients though. I just wonder if there is a way to reduce the issue, roger beep installed or not.

 

[Robb]

Perhaps a well-placed disc cap with the right value on both sides of the relay may curb most of the pop.
Just a thought . . .

 

[Shockwave]

The problem that existed before the roger beep would only be noticed when the mic was unkeyed very quickly. That defeats the momentary delay in turning on the speaker so the pop couldn't be muted. Now with the roger beep installed the pop consistently takes place regardless of how fast or slow you let go of the mic button because it no longer controls the receiver speaker, the relay does.

Because these switching transients are in the audio stage and not the DC line, capacitors that may reduce the pop will have just as much effect on the desired audio as they will on reducing the pop. Capacitors are actually part of the problem since they have to charge when the circuit is energized. The correct way to resolve these issues is through proper sequencing of the required transmit and receive connections. Simply put, the RX speaker should be the first thing that goes off during the key process and the last thing to connect when returning to RX.

 

[darklife]

The problem that existed before the roger beep would only be noticed when the mic was unkeyed very quickly. That defeats the momentary delay in turning on the speaker so the pop couldn't be muted. Now with the roger beep installed the pop consistently takes place regardless of how fast or slow you let go of the mic button because it no longer controls the receiver speaker, the relay does.

Because these switching transients are in the audio stage and not the DC line, capacitors that may reduce the pop will have just as much effect on the desired audio as they will on reducing the pop. Capacitors are actually part of the problem since they have to charge when the circuit is energized. The correct way to resolve these issues is through proper sequencing of the required transmit and receive connections. Simply put, the RX speaker should be the first thing that goes off during the key process and the last thing to connect when returning to RX.

Ah so there is no real workaround besides adding another relay with a very short delay to mute the speaker.
Well in that case screw it lol. I am not going to tack on more circuitry to something that already works fine just to null a simple problem like that.
Glad to know this is a common problem so I don't feel so stupid

 

[loosecannon]

im wondering if there is an electrolytic cap in this chassis that causes a short time delay before the speaker is engaged upon mic button release?

if there is, and that cap has dried out due to old age, couldnt this cause the speaker pop you are experiencing?

just some thoughts...
LC