DCS audio cuts out

KC7RBW
Posts: 185
Joined: Wed Nov 20, 2019 1:23 am

Re: DCS audio cuts out

Post by KC7RBW » Sun Sep 13, 2020 4:18 pm

Riku wrote:
Sun Sep 13, 2020 6:05 am
oh1fss wrote:
Wed Sep 09, 2020 3:50 pm
I compared versions Jul 31 2020 and the new one (Aug 30 2020) on Baofeng DM-5R Plus. The new version tolerates overdeviation better than the old one, but there are still some cuts when receiving such a signal. The signal had a CTCSS tone.
thanks for the fix, however:
We tested on new radios, same thing it is slightly better but breaking up still when just use other opengd77 radio and say "AAAA" there, its not hardware issue.
Can you tell us more about your experiment setup? What power is the transmitter set to, how far apart, what kind of antenna (or attenuators and cables), etc.? What's the squelch set to, and which tone(s)?

This "AAAA" thing you're talking about sounds a lot like the "talk off" problem described here (look for a whole section on "talk off" and related problems. These problems are in the transmitter, not in the receiver. If the transmitter is working correctly (has the right filters in the right stages doing their job well) transmitted audio can't interfere with the sub-audible tone.

There's other useful information at the site I linked above, like avoiding tones that are close to harmonics of your AC power mains, and using tones between 127.3 Hz and 173.8 Hz.

Since you say the transmitter was opengd77 also we could look at if the AT1846S is really configured correctly for transmit (especially that the right filters are enabled). It lets you configure it incorrectly if you think you have a reason to, but I think it's already correct. You could be running into limitations of the (transmitter) hardware.

I'm also basically suspicious of how the whole squelch system in OpenGD77 is set up. It's doing a lot of things in firmware that the AT1846S is capable of doing for itself, and which I suspect it's probably better at than we are.

I also don't quite grasp why we rely so heavily on the traditional squelch rather than solely or mostly on the tone and code squelches when they are configured. I get that noise can trigger the decoder but that's why we wait until we see the decoder hold a while before we open and why we hang a while after the decoder loses the signal (unless we have STE, which is not implemented yet in the firmware but the AT1846S supports).

I've not been doing a lot of OpenGD77 hacking lately, so someone else may want to experiment with these things.
Andrew | KC7RBW | ajorg

oh1fss
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Joined: Mon May 04, 2020 11:53 am

Re: DCS audio cuts out

Post by oh1fss » Sun Sep 13, 2020 7:53 pm

The problem can be reproduced easily. We have a repeater which uses CTCSS 103.5 Hz on receive and transmit. Wide deviation or loud audio makes the problem appear. I believe the repeater has Motorola radios?

Another way of reproducing the problem was a simplex QSO when a GD77 was transmitting and we used two DM-5R Plus radios on receiving, one had OpenRD5R built on Jul 31 2020 and the other had build date Aug 30 2020. We used CTCSS 103.5 Hz, and both of the radios had the problem, although the Aug 30 2020 version was much better.

The problem appears also when GD77 is used as the receiving radio.

Early versions of OpenGD77 did not have the problem. The problem appeared sometime in the spring, perhaps around April?

Other radios do not have this problem, only some versions of OpenGD77/OpenRD5R.

Propably the deviation is too wide. Unfortunately, too many hams use too wide deviation. I think we just have to cope with too wide deviation also in OpenGD77 - thats what the other radios do as well. It's not very fruitful to be the only purist in the world.

VK3KYY
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Re: DCS audio cuts out

Post by VK3KYY » Sun Sep 13, 2020 10:10 pm

KC7RBW wrote:
Sun Sep 13, 2020 4:18 pm

I'm also basically suspicious of how the whole squelch system in OpenGD77 is set up. It's doing a lot of things in firmware that the AT1846S is capable of doing for itself, and which I suspect it's probably better at than we are.
The FM squelch control dates back to the code Kai originally wrote.
I don't know why he chose to read the RSSI and Noise register and use the "Noise" data for the squelch.

I presume that this is what the official firmware does.

Although the AT1846S can be configured to use one of its GPIO connections as a squelch indication pin, I know that none of the GPIO pins on the AT1846S are connected to the mircocontroller in the GD77 (or DM-1801 or RD-5R).

So the AT1846S would still need to be polled even if some sort of internal squelch control could be used. It looks like bit0 of register 0x1C contains the "Sq compare result"

However, it would take a considerable amount of time to research whether the internal squelch in the AT1846S works well, and whether its any better than the system of using the "Noise" value thats currently used.



You could try posting an issue onto the HamDV/OpenGD77 github reqo as a question to Kai, asking why he chose not to use the squelch detection in the AT1846, and he may reply, but I've not heard from Kai for quite a long time, and from what I can remember he is busy doing other projects.

Riku
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Re: DCS audio cuts out

Post by Riku » Mon Sep 14, 2020 4:16 pm

KC7RBW wrote:
Sun Sep 13, 2020 4:18 pm
Can you tell us more about your experiment setup? What power is the transmitter set to, how far apart, what kind of antenna (or attenuators and cables), etc.? What's the squelch set to, and which tone(s)?
any setup will do as long you use opengd77 radios, set rx and tx any ctcss and very important you mouth need to touch the radio so you can do "overmodulation" and say aaaa or something very loud.
i have described about this setup many times. i just feal no one is listening me how to reproduce this. the mouth need to be touched into the plastic at mic position to get this working. im very sure it is not hardware issue, we have tried so many radios here and all of them does this.

old video showing this problem...: (radio on the right has my fix i did to correct this problem)

youtu.be/VEudaakpI08
Riku / OH1E
facebook fan group: https://facebook.com/groups/OpenGD77/

KC7RBW
Posts: 185
Joined: Wed Nov 20, 2019 1:23 am

Re: DCS audio cuts out

Post by KC7RBW » Wed Sep 16, 2020 2:43 am

Riku wrote:
Mon Sep 14, 2020 4:16 pm
any setup will do as long you use opengd77 radios, set rx and tx any ctcss and very important you mouth need to touch the radio so you can do "overmodulation" and say aaaa or something very loud.
i have described about this setup many times. i just feal no one is listening me how to reproduce this. the mouth need to be touched into the plastic at mic position to get this working. im very sure it is not hardware issue, we have tried so many radios here and all of them does this.

old video showing this problem...: (radio on the right has my fix i did to correct this problem)
Hi Riku! I don't know if you've taken a look, but the fix we merged (#727) for this is functionally the same as the fix you proposed in #670 with the exception of the length of time it tolerates loss of the tone. Please have a look at both changes in context and let me know if you see other differences. Some differences you might see are due to other changes that were added between when you posted and when I re-posted the change. Others are just collapsing the logic for less duplicated code.

It should be easy for you to check if extending the time we tolerate fixes your issue completely. Let us know. Unfortunately the longer we tolerate the loss of tone the longer the squelch tail, which many operators will find obnoxious (until we implement squelch tail elimination, and even then where it's not supported).
Andrew | KC7RBW | ajorg

KC7RBW
Posts: 185
Joined: Wed Nov 20, 2019 1:23 am

Re: DCS audio cuts out

Post by KC7RBW » Wed Sep 16, 2020 2:57 am

VK3KYY wrote:
Sun Sep 13, 2020 10:10 pm
Although the AT1846S can be configured to use one of its GPIO connections as a squelch indication pin, I know that none of the GPIO pins on the AT1846S are connected to the mircocontroller in the GD77 (or DM-1801 or RD-5R).

So the AT1846S would still need to be polled even if some sort of internal squelch control could be used. It looks like bit0 of register 0x1C contains the "Sq compare result"

However, it would take a considerable amount of time to research whether the internal squelch in the AT1846S works well, and whether its any better than the system of using the "Noise" value thats currently used.
Well it's unfortunate that the GPIO isn't available, but reading just the "sq compared result" sounds like it would be worth a shot.

If I or someone else gets around to implementing a branch that works that way we can post the experimental build and wait until the folks who see these problems report back if the AT1846S does a better job than the current implementation. It's not a high priority for me, but curiosity may get to me.
Andrew | KC7RBW | ajorg

G4EML
Posts: 240
Joined: Sat Nov 16, 2019 10:01 am

Re: DCS audio cuts out

Post by G4EML » Wed Sep 16, 2020 10:26 am

Increasing the hang time for loss of tone decode will not normally cause an increase in the length of the squelch tail on a clear channel because the carrier squelch will still mute the radio on loss of signal. It will however be noticeable on a channel where the carrier squelch does not work, such as if there is interference or other traffic using different tones. (Probably the main reason for using Tone decode on receive). It could probably be increased a little without being too objectionable.

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