Hi, I have some cheap VHF ham radios that I use with a speaker-mic. I get an annoying "click" or "pop" sound from the speaker in the speaker-mic whenever the radio begins or ends receiving a transmission. It happens even with the volume turned all the way down. So if there is interference or radio chatter I don't want to listen to, so I turn the volume down, then I have to listen to these click-clicks all the time. I also get the same click when the radio first turns on (which doesn't bother me but I mention it because it might be a clue). I'll also mention that this happens everywhere, all the time, with any received signal, so it's not some RF interference making it's way into the audio circuit.

It only happens when the speaker-mic is plugged in. The built-in speaker does not have this problem. I have tried 6 different radios (3 different models) and 5 different speaker-mics (two different models), they all do it. Most are so quiet you don't really notice it, but the radios I prefer to use the most have a loud click.

Is there anything I can do inside the speaker-mic circuit that might help? The characteristic of the sound makes me think that it's a DC voltage or change in voltage that is causing it. I did try adding a capacitor inline with the audio feed but all that did was make all the audio more quiet.

Could it be an impedance mismatch? I found some website (I'm unsure of it's reliability) that said the speaker in this speaker-mic is 16 ohms.

Thanks for any help.

 

Try a 10 uF electrolytic capacitor in series with the speaker, it might be a DC voltage pulse.

 

A series capacitor for the speaker may help, als a shunt capacitor between the + 5 volts and the negative ground side (sleeve of the 2.5mm connector. And maybe a 1 mfd capacitor in series with the speaker if the 10 mfd does not fix the problem. But the best solution may be an external speaker, not part of the speaker-mic package.

 

A series capacitor for the speaker may help, als a shunt capacitor between the + 5 volts and the negative ground side (sleeve of the 2.5mm connector. And maybe a 1 mfd capacitor in series with the speaker if the 10 mfd does not fix the problem. But the best solution may be an external speaker, not part of the speaker-mic package.

Thanks.

Both of my two models of speaker-mic have a 3.5mm jack where you can plug in an external speaker. When I tried this, the external speaker (which is a communications speaker that I believe to be 8ohms) had the same clicks.

 

What can I say?? I have used a Radio Shack HT with external power, antenna, Microphone, and external speaker as a cheap mobil radio for 20+ years and never noticed that click.
I did actually try using the HTX202 with a borrowed speaker/mic when I first bought the radio. I did not like anything about the speaker/mic and returned it after a couple hours.
I am not aware of that click at all, from any of my VHF radios since then. And an impedance-mismatch would not cause a click, which certainly is some sort of DC artifact.
I suggest using the external speaker and experimenting with a series capacitor to block the DC. And see if you cam measure the DC voltage that appears.If it is only a momentary pulse that is one thing, if it is steady DC then there is a more serious problem.

 

I made a video demonstrating the problem. You can kind of hear the clicks in the beginning, when I have the volume turned up. Then I turn the volume down and the clicks are more obvious.

Someone might suggest it's RF energy from the radio so close. But as I mentioned, it happens all the time, with every transmission, even those many miles away. It's perfectly timed to the receive LED on the top of the radio (also the "antenna" icon on the LCD). Anytime the radio begins receiving a transmission or stops receiving a transmission, it produces these clicks.

I will open up the speaker mic and play with inserting a capacitor. When I tried that previously (using the audio output jack on the mic), it had no affect. But I'm about ready to just sell these Chinese radios and buy some Japanese ones instead. But you can't beat 10W out and a synced display (shows both the frequency and the name) for $50.

http://imgur.com/a/vW08vqB

 

If you can get a circuit schematic for the radio it should be possible to discover the cause.
While examining that circuit for the speaker-mic in the first post, it hits me that a TX data line is in the same pair. So if you can get a 3 circuit 2.5 mm plug, try connecting a different speaker pair to only the tip and sleeve connections. The problem might be in the speaker-mic cable. OR it might be in a poor connection to the 2.5mm jack side.

 

Wow there are a lot more components in here than I expected. I wonder why? I thought it would just be a switch, a microphone, and a speaker.

 

What I think that I see is that the number of wires from the double connector does not match the published circuit that was presented earlier.There might be two black wires in the connector but it is hard to tell.
But if the circuit doesnot agree with reality then it is a different challenge.

 

The pin-out for the dual jack plug is as I posted. All these speaker-mics are compatible with many different radios, they all use that same pin out. I don't know what the electronics are inside the mic though. That is puzzling. There is a +5v feed, so there could be some active circuits in here.

I plan to acquire some Japanese brand radios (Icom, Yaesu, Kenwood, etc) and see if they have the same issue.

 

Perhaps other HAM RADIO operators can share their experience. Certainly that spkrmic is not compatible with my HTX202. I use a seperate speaker and Mic because the OEM speaker-mic sounded really bad.

 

Google "pop from radio squelch".

 

Ok I ordered some capacitors and schottky diodes to do some testing. @Ron H thank you for mentioning that term. That led me to some helpful information. I even bought an oscilloscope so I could measure the results.

As I expected it is a DC pop. And a better way to describe it, rather than related to receiving transmissions, is any time the audio amp chip comes online, there is a DC pop. And a smaller one when it turns off. So this means it happens every time you press a button also.

The schottky diode across the terminals (I tried two, one in each direction, but that didn't work better than just one) worked fairly well. It's still a too-loud, harsh sound, but it was noticeably less irritating.

The 100uf ceramic capacitor did even better. Oddly when I had both the diodes and capacitor in the circuit, it was just as bad or worse then when I had neither in the circuit. I'm going to end up using the capacitor since it affects the audio quality less so than the diode does.

Thanks for the help!

Stock, with no modifications.


With the diode in place:


With the capacitor in place:


I wonder what they did to the audio circuit internally, that makes the pop so quiet? (the pop is only a problem when I connect an external speaker mic. The internal speaker barely makes a sound).

Also do you notice how the wave form is distorted after adding the capacitor? It's sometimes below 0 now? I can't hear any real change in quality, but I'm curious to hear from some more experienced people on what is happening here.

 

I suggest now trying a much lower value capacitor. Also, try a capacitor IN SERIES with the speaker, because I see that the DC level is rather different with the capacitor in parallel.

 

I suggest now trying a much lower value capacitor. Also, try a capacitor IN SERIES with the speaker, because I see that the DC level is rather different with the capacitor in parallel.

Yes the capacitor was connected in series. The diode was in parallel.

What do you expect would happen with a lower value capacitor? I bought these 100uf caps and don't really have anything lower. I do have 10 1uf caps, and I connected them all in parallel which should have been 10uf of capacitance. And it cut out so much audio that I could barely hear anything. But they were from a cap assortment I bought directly from china, maybe they are just crap components.

Update - after a little googling it seems I should be able to connect two of my 100uf caps in series and end up with 50uf of capacitance. I could try that. But I'd like to know what you would expect to happen. My understanding is it would raise the cut off frequency (i.e. the audio may sound tinnier, with less bass response).

I'll also mention I did try two 100uf capacitors in parallel, and I couldn't really tell any difference from one cap.

 

You mentioned there is +5V in there, is there any way to disconnect that? To eliminate the 5V isn't causing the pop.
The mic in the spk/mic would need biasing, but that may be coming from the radio, or the 5V is used in series with a resistor to do the biasing, so you may lose the mic and/or TX via the spk/mic temporarily while the 5V is disconnected. I am hoping the speaker will still work to see if it still pops.

I think the easiest way of disconnecting the 5V may be by removing the wire from the connector, if you use a pin to push the latch on the particular pin, it should just slip out, and then you can just put it back in and lift the latch bit of the pin, if that makes sense.

 

My observation of speaker-mic connectors is that they are molded onto the cable and not at all accessible for any purpose, including repair. So connector changes are probably not possible.

The reason for changing the capacitance was to reduce the low frequency response. experimenting with different capacitor values is probably a very reasonable approach.

 

Did a little surgery on the speaker-mic this morning to install the 100uf cap. Works much better now. Thanks for the help everyone.

 

In old point to point wiring, that popping noise was typically noise from a resistor failing. Poking around carefully on the powered up resistors with a thin wooden rod could quickly find which one was the culprit. Maybe lightly tapping on SMD ones?