Audio Stuttering

M6XCX
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Re: Audio Stuttering

Post by M6XCX » Sun Jan 26, 2020 1:13 am

So, after adjusting it one step at a time and then testing, I found no change in the stuttering when at the hotspot frequency. I then discovered that I was actually changing VHF not UHF! :shock:

I then started again (on UHF this time!), and took it down one at a time from 996 to (eventually) 990, and that seems to be about right. I'm still getting the odd blip, but very rarely, and it's more than good enough for me. I may take it down a few more tomorrow morning as a test but time for bed now.

Problem solved, thank you very much! 8-)

Tony.

VK3KYY
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Re: Audio Stuttering

Post by VK3KYY » Sun Jan 26, 2020 3:07 am

OK

The 990 is probably one of the lowest values I have seen, but I think some files people sent me went as low as 985

What value was originally in the radio ?

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m1dyp
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Re: Audio Stuttering

Post by m1dyp » Sun Jan 26, 2020 9:00 am

i took my uhf reference oscillator tuning value from 993 to 990, to fine tune it
73 de Ken :D

VK3KYY
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Re: Audio Stuttering

Post by VK3KYY » Sun Jan 26, 2020 9:22 am

Hi Ken

OK.
Its amazing what a small change in osc value can do !

I think the problem must partially be something to do with the modulation from the Hotspot, as minor miss-calibrations don't seem to cause any problems on real repeaters


Also, what we still don't know is why the official firmware seems more tollerant of the osc freq not being correct.

I have noticed whilst doing some logic analyser data captures, that the official firmware seems to sent a load more data to the C6000 as part of the setup and even when changing channels, and I suspect the data may be related to the signal filtering or possibly the 4FSK decoding.
Unfortunately we have very little documentation on the C6000 DMR chip :-(

When I get time, I may try decoding the logic analyser data and then write some code to send those data blocks to the C6000, but for most people it these additional data blocks don't seem necessary, so they can only make minor changes to the decoding (if in fact that's what the data actually controls)

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m1dyp
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Re: Audio Stuttering

Post by m1dyp » Sun Jan 26, 2020 9:51 am

i'm convinced it's my dvmega blue stack.

Both my jumbo spots have been great from day one.

Had i not acquired a jumbo spot, i would never have known, as there are no repeaters near me :{

It's all about experimenting, that's half the fun :D
73 de Ken :D

G4EML
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Re: Audio Stuttering

Post by G4EML » Sun Jan 26, 2020 10:38 am

if fine tuning the radio’s frequency makes a difference it could be that the hotspot has a higher deviation than it should, or is itself off frequency. That could be causing distortion in the GD77 receiver due to the filtering. Fine tuning could be minimising the distortion.

One thing I have wondered is if we are using the correct receiver bandwidth. I know it is currently forced to 12.5KHz for DMR. DMR is designed to work in 12.5KHz channels so that would seem reasonable but it does use the channel close to the limits. From my experience with using various radios with MMDVM repeaters the standard 12.5KHz filtering can be a bit too tight for DMR. Often the radios work better with the receive filtering set to 25KHz.
It might be worth trying. It could explain why the official firmware is more tolerant of frequency error.

Colin G4EML

F6GVE
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Re: Audio Stuttering

Post by F6GVE » Sun Jan 26, 2020 11:20 am

I thought too about the possible excessive deviation.
What I can say is that I spent hours, I should say days, in ajusting as better as possible the frequencies, the clock, but the stuttering is still here.
It is better than before but it still happens.
It happens no matter the RX level, no matter how long the station is transmitting.

The only way I have found to get rid of this is to shift the frequency frankly. I don't remember if I must shift up or down. However obviously I am off frequency, the GD77 DMR sensitivity becomes lower, I must be close to my hotspot. I adjust my hotspot RXOffset and TXOffset something like RXOffset 100 and TXOffset 1000 (I don't remember exactly but it was something like that)
Doing this, I have no stuttering but I am clearly off frequency. Just an example, if the frequency is set to 434 MHz in VFO mode, I cannot receive on 433.9995 but I can still receive on 434.0020 (may be it is 433.9980 and 434.0005 I don't remember)

M6XCX
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Re: Audio Stuttering

Post by M6XCX » Sun Jan 26, 2020 6:35 pm

VK3KYY wrote:
Sun Jan 26, 2020 3:07 am
OK

The 990 is probably one of the lowest values I have seen, but I think some files people sent me went as low as 985

What value was originally in the radio ?
Original value was 996. Today I've been dropping it by one and listening until it stutters. The lower I go, the bigger the gap between a stutter. I ran 987 for 25 mins without a single stutter which is more than good enough. But have moved to 986 out of interest.

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Re: Audio Stuttering

Post by VK3KYY » Sun Jan 26, 2020 9:10 pm

Ok. Those values are quite low.

I don’t know if you also use your radio with a repeater, as you may have problems if the value is being set to match your Hotspot, as a Jumbospot etc is not a good calibration reference

M6XCX
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Re: Audio Stuttering

Post by M6XCX » Sun Jan 26, 2020 10:55 pm

VK3KYY wrote:
Sun Jan 26, 2020 9:10 pm
Ok. Those values are quite low.

I don’t know if you also use your radio with a repeater, as you may have problems if the value is being set to match your Hotspot, as a Jumbospot etc is not a good calibration reference
Ok, so given your steer here, as well as previous comments on the thread about the firmware maybe not being as forgiving around deviation, I took F6GVE's advice and played with the hotspot offset.

I have been getting 1.6 / 1.7% BER so far with it and as it was green accepted it. However, moving the offsets from the installed config of -450, I found -300 as a sweet spot, taking BER down to 0.3%. The Anytone was happy with both settings and received on both without any stuttering.

I then set about starting the oGD77 OSC back to 1000, which gave me heavy stuttering, but have landed at 990, and 30 mins have gone by without a single stutter.

So it seems that the hotspot was indeed off, and improving it as well as the minor tweak to the OSC has sorted it. Will try and test the oGD77 with a repeater on the way to work tomorrow.

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