Slight ticking sound

[do1jml]

I did a few simple tests between the different radios I have. I am not so sure that the noise is linked to the open firmware.

One of my radio has the noise on receive and transmit. It is the one I used the most. The other, including the one with the manufacturer firmware also have the noise, but at a much lower level. If my attention had not been brought to it, I would not have noticed it.

The TX noise is present on DMR all the time, whatever the backlight level.

The noise is only present on FM when the backlight is on, in RX and TX.

A possible explanation is poor RF shielding. The noise would either come from the backlight power regulation or from the DMR TDMA pulsing. If there is neither backlight nor DMR -> no noise. Either one is audible and the noise spectrum may be similar enough to sound the same for the user.

I intend to open the offending radio to see if there is something obvious about the shielding. From published pictures, it seems that the back case acts as a shield together with traces on the PCB. The contact between the two may degrade with time, especially it there are small movements between the two. The conductive paint on the back case may wear off or the contact zone may oxidize.

[VK3KYY]

Very interesting...

I don't think the problem is the shielding because its independent of power level.
E.g. set the radio to the User Defined power level, and then adjust this to the absolute minimum where you can still hear the transmission.
This will be just a few mW, and the noise level is identical.

There was also some speculation that the dimming control of the backlight caused the problem, however I built a special version without dimming and the problem still occurred, hence its not the 10kHz PWM signal which is causing this problem.

However one interesting thing is that when the PWM was originally at a lower frequency, I could hear the PWM as a tone on the RX audio on the DM1801

Hence I changed the PWM to be outside the audible range, and this resolved that problem on my DM1801

[do1jml]

I can confirm that the noise is independent of the power level. I tried with 50 mW.

The interesting part is that if I use FM and switch backlight off, the noise is gone.

[do1jml]

I disassembled the radio today, looked at the back paint contact zones and cleaned it with contact spray. Unfortunately, I do not notice much difference as to ticking noise... sorry.

[VK3KYY]

I had an idea that this may be caused by the keypad read function, as it is run every 1ms and strobes the keypad matrix lines at high speed.

However I made a version which did not read the keypad during DMR Tx and sent it to someone who has the motor boating problem, and it made no difference.

So the keypad reading is not the problem

[G4EML]

Roger,

I also have not heard the problem on my radios so it’s difficult to diagnose.

One possible cause could be the screen update. The microphone signal shares the same ribbon cable as the screen and keyboard.
Have you tried a version which doesn’t write to the screen during Tx?

Colin.

[VK3KYY]

Roger,

I also have not heard the problem on my radios so it’s difficult to diagnose.

One possible cause could be the screen update. The microphone signal shares the same ribbon cable as the screen and keyboard.
Have you tried a version which doesn’t write to the screen during Tx?

Colin.

I'd need to double check the code is not doing something unexpected, but during Tx it should only be updating the screen once per second, to change the counter.

This problem sounds much more like DMR pulse timing, i.e every 30ms.

But I'll check whether this display is doing unexpected renders during Tx.

[VK3KYY]

Well, I was wrong.

The microphone meter bar graph is rendered a lot more often, around every 10mS

So that is definitely a potential cause of the problem.

I'll investigate this to confirm whether the screen update is causing the ticking noise.

[VK3KYY]

To update this.

Several people have tested a version which only updates the screen, once per second, and the problem still seems to be present.

So it doesn't look like its the screen updates which are causing the problem.

[do1jml]

On my GD-77, the ticking sound disappears if I turn down the backlight and use FM. I do not need to turn the backlight completely off, actually.

This point out to the backlight being one of the causes, but not necessarily the only cause. I get the sound, albeit reduced, in DMR without backlight.

But, when people test a new firmware with changed keypad reading, did you advise them to switch off backlight? If you did not, some testers will use backlight, some not and you may get inconsistent results.

Also: aren't the screen and keypad still active in FM mode? If they are, the fact that my radio, which is sensitive to the interference, does not exhibit the sound in FM would speak against the screen or keypad being the source.