DMR radio interference with headset

[blhar15]

Not sure if this is the right forum for this, but I am working with Motorola DMR radios, using Peltor Comtac headsets (noise cancelling) with the 3M wired PTT. When you have the headset noise cancelling feature on and you transmit there is feedback, interference in the headsets. It only does this when using digital, in analog mode there is no interference.

Does anyone have experience with this or know why a digital radio would cause this on a headset?

Thank you

 

[KevinC]

Not sure if this is the right forum for this, but I am working with Motorola DMR radios, using Peltor Comtac headsets (noise cancelling) with the 3M wired PTT. When you have the headset noise cancelling feature on and you transmit there is feedback, interference in the headsets. It only does this when using digital, in analog mode there is no interference.

Does anyone have experience with this or know why a digital radio would cause this on a headset?

Thank you

A pulsed sound? If so RF is getting the audio amp of the headset somewhere. Get with the headset company and work with them.

 

[G7RUX]

Not sure if this is the right forum for this, but I am working with Motorola DMR radios, using Peltor Comtac headsets (noise cancelling) with the 3M wired PTT. When you have the headset noise cancelling feature on and you transmit there is feedback, interference in the headsets. It only does this when using digital, in analog mode there is no interference.

Does anyone have experience with this or know why a digital radio would cause this on a headset?

Thank you

Since DMR uses two timeslots of length 30ms you are likely hearing this “chopping” at 33 Hz or so, plus a load of harmonics so it will sound like a harsh buzzing. This is likely happening because RF is getting into the audio feed into the noise cancelling amplifier(s), perhaps via the NC microphones…does it do it if the noise cancelling is turned off?
Whether it does or doesn’t, if you are using genuine 3M Peltor headsets and genuine adaptor cables then (a) check and clean all of the connectors and if that doesn’t fix it then get in touch with the supplier as there is an issue.

Note that the headset plug needs a good firm push to seat it properly in the PTT adaptor.

 

[blhar15]

I appreciate the replies. Yes, it is kind of a pulsing sound. If you turn the headset off, so it is not in noise amplification mode, then no, you cannot hear the sound. Considering I have multiple headsets, and multiple push to talk adapters and it does it on each one, I am beginning to think these Comtac III headsets will not work with DMR radio. This is all genuine 3M gear, headsets and PTT cables. I also have some TYT DMR radios and it does the same thing. If it only did it with one or two, I could say it was an issue with the equipment. Also the plug is seated good in the PTT adaptor.

I wonder if the newer Comtac V or VI models have corrected for this, as the III's were released in 2010 before digital radios were really big. This article talks about that a bit with the release of the newer models. Even says to make them more compatible with the P25 radios.
3M Discontinues Popular ComTac III Headset

 

[mmckenna]

Common issue with TDMA radios and poorly shielded audio accessories.
Kenwood released new speaker mics when they started selling DMR radios.

A bluetooth headset would probably work. Or, contact 3M and ask them which of their wired headsets will work with DMR/TDMA radios.

 

[KevinC]

I appreciate the replies.

You're very welcome.

 

[G7RUX]

I appreciate the replies. Yes, it is kind of a pulsing sound. If you turn the headset off, so it is not in noise amplification mode, then no, you cannot hear the sound. Considering I have multiple headsets, and multiple push to talk adapters and it does it on each one, I am beginning to think these Comtac III headsets will not work with DMR radio. This is all genuine 3M gear, headsets and PTT cables. I also have some TYT DMR radios and it does the same thing. If it only did it with one or two, I could say it was an issue with the equipment. Also the plug is seated good in the PTT adaptor.

I wonder if the newer Comtac V or VI models have corrected for this, as the III's were released in 2010 before digital radios were really big. This article talks about that a bit with the release of the newer models. Even says to make them more compatible with the P25 radios.
3M Discontinues Popular ComTac III Headset

I have various 3M Peltors in use, including ComTac2/3/4 headsets in use with TETRA and DMR and none of these do this.

 

[blhar15]

Well that is interesting your Comtac's are working. Is there something different with the Tetra radios and the TDMA feature. I get the same problem with the TYT DMR radios. In my testing, I tried not even plugging the headset into the radio PTT. As long as the radio is close to the headset when you key up you can still here the pulsing sound. There is something with the headset noise cancelling, amplifying feature that is picking this up from the radio.

 

[mmckenna]

TETRA would likely be much lower power than your DMR radios.

 

[KevinC]

TETRA would likely be much lower power than your DMR radios.

I believe TETRA uses adaptive power, so depending on how well the BTS receives you the TX power could be greatly reduced.

 

[G7RUX]

TETRA would likely be much lower power than your DMR radios.

TETRA handsets usually transmit in the 1-3 W power output range, compared with 1-5 W for typical DMR handsets so broadly similar power outputs.

TETRA uses four timeslots per carrier, usually one control and three for user data. Hence the choppiness tends to sound rather higher in frequency, although the peak-to-mean ratio is lower than for DMR, so the audibility of the effect should be lower. The peak-to-mean or CCDF depends greatly on the data being transmitted and how many slots are in acive use by the handsets so it’s hard to say just how it will sound and how much of an effect you will see out in the wild compared to test conditions in a lab.

 

[G7RUX]

I believe TETRA uses adaptive power, so depending on how well the BTS receives you the TX power could be greatly reduced.

It does, it’s a variety of managed cellular system.

 

[mmckenna]

Is there something different with the Tetra radios and the TDMA feature.

I think this is part of your answer:

It does, it’s a variety of managed cellular system.

Many years ago, some cell carriers used TDMA and a lot of audio devices would pick up noise from the cell phones. We had some conference phones at work that had a sticker on them that proudly proclaimed "No Cell Phone Buzz!" Which just meant they properly shielded their products.

 

[IU0LFT]

Not sure if this is the right forum for this, but I am working with Motorola DMR radios, using Peltor Comtac headsets (noise cancelling) with the 3M wired PTT. When you have the headset noise cancelling feature on and you transmit there is feedback, interference in the headsets. It only does this when using digital, in analog mode there is no interference.

Does anyone have experience with this or know why a digital radio would cause this on a headset?

Thank you

Hi, as you have to test some solutions, try first this one,
a 100pf capacitor in parallel with the microphone