whoosh sound at ends of DMR transmissions

wa2n
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Joined: Thu Apr 08, 2021 5:34 am

whoosh sound at ends of DMR transmissions

Post by wa2n » Fri Apr 23, 2021 3:15 pm

I'm running the last firmware from April 3rd and have always heard a sshhh or wooshh sound at the beginning or end of a transmission coming from my pi-star hotspot. I've only owned my three GD-77's for a couple weeks and immediately installed OpenGD77, so I thought this behavior was normal. Yesterday I also bought an Anytone AT-D878UVII Plus which is quiet at the ends of the transmission. So is this an artifact of the very latest release, or a characteristic of the hardware itself in the OpenGD77? I'm set up in promiscous mode on both the GD-77's and Anytone radios. Is there any way to eliminate the noise at ends of transmission?

wa2n
Posts: 20
Joined: Thu Apr 08, 2021 5:34 am

Re: whoosh sound at ends of DMR transmissions

Post by wa2n » Fri Apr 23, 2021 6:17 pm

Here's a link to a short video which illustrates the squawks that occur at the beginning or tail end of transmission sometimes. My firmware is the latest version from April 3, 2021. All three radios behave the same. https://photos.app.goo.gl/ZTLZLks5EhBCpgBP8

wa2n
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Joined: Thu Apr 08, 2021 5:34 am

Re: whoosh sound at ends of DMR transmissions

Post by wa2n » Fri Apr 23, 2021 7:16 pm

I was able to eliminate most of the squawking by enabling the DMR RxG filter.

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F1RMB
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Location: Grenoble, France

Re: whoosh sound at ends of DMR transmissions

Post by F1RMB » Fri Apr 23, 2021 7:38 pm

Hi,

Do not disable CC filtering.
You can disable it when you want to discover the colorcode, only.


Cheers,
---
Daniel

wa2n
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Joined: Thu Apr 08, 2021 5:34 am

Re: whoosh sound at ends of DMR transmissions

Post by wa2n » Fri Apr 23, 2021 11:07 pm

Thanks Daniel.

VK3KYY
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Location: Melbourne, Australia

Re: whoosh sound at ends of DMR transmissions

Post by VK3KYY » Sat Apr 24, 2021 1:45 am

wa2n wrote:
Fri Apr 23, 2021 11:07 pm
Thanks Daniel.
Its good to know what the CC filter setting was causing the problem

Unfortunately the CC filter can't really be disabled in the hardware. Colin G4EML wrote some clever code to look at the incoming CC and then try to use that CC.
But as the incoming DMR signal data CC value is initially noisy, it takes some time for the CC to stabilise, and it likes this whoosh effect is a byproduct of the noise on the CC data, or Colins algorithm.

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

Re: whoosh sound at ends of DMR transmissions

Post by G4EML » Sat Apr 24, 2021 9:21 am

The HR-C6000 DMR chip and the firmware normally check the CC to ensure that the received signal is valid. This check is built into the hardware. I managed to find a way of disabling it to allow the CC filtering to be turned off. This is using the chip in a way that was not intended by its manufacturers. Unfortunately this can result in the bursts of noise you are hearing when the signal starts and stops.

In commercial use a DMR radio would never need this feature. However it is a useful tool for amateur radio use.

As Daniel says, this feature is not intended to be used for normal reception. It should only be used for a short time to detect the correct CC for a new signal and then that CC can be entered in the channel details menu.

Colin.

IZ2EIB
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Joined: Sat Nov 30, 2019 12:55 pm

Re: whoosh sound at ends of DMR transmissions

Post by IZ2EIB » Sat Apr 24, 2021 11:39 am

Hi everybody.
For what can be worth and can be useful, in any condition I have never encountered the specific problem, nor other similar (motorboat's sound, hiss or whistles with battery fully charged), including use of the transceiver with CC disabled.
Indeed, honestly I have to admit to use my GD-77 often using all the filters deactivated (TG, Timeslot, DC, CTCSS, etc, etc ...) by scanning all channels in memory (over 900) without ever having found any audio problem.
I know that the problem could be attributable to hardware differences introduced during the production of the transceiver.
In any case my GD-77 has serial number 1709A13851 (ninth week of the year 2017), bought in January 2018.

73 best regards de Fabio IZ2EIB

ok1pt
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Joined: Mon Jul 20, 2020 3:38 am

Re: whoosh sound at ends of DMR transmissions

Post by ok1pt » Sat Apr 24, 2021 6:07 pm

IZ2EIB wrote:
Sat Apr 24, 2021 11:39 am
Hi everybody.
For what can be worth and can be useful, in any condition I have never encountered the specific problem, nor other similar (motorboat's sound, hiss or whistles with battery fully charged), including use of the transceiver with CC disabled.
Indeed, honestly I have to admit to use my GD-77 often using all the filters deactivated (TG, Timeslot, DC, CTCSS, etc, etc ...) by scanning all channels in memory (over 900) without ever having found any audio problem.
I know that the problem could be attributable to hardware differences introduced during the production of the transceiver.
In any case my GD-77 has serial number 1709A13851 (ninth week of the year 2017), bought in January 2018.

73 best regards de Fabio IZ2EIB
Very interesting!
My GD-77 is 1709A08252, so the difference seems to be 5599 pieces :-). And my one doesn't like CC filter off, it makes various strange sounds when the signal appears and disappears (but they don't sound like whoosh, it's more like buzzing, humming or whistling - just elementary sounds from which the codec constructs the voice). And if the battery is full, the audio from the speaker is a bit distorted - it tan be heard better in low volumes, so I believe it's something with transient distortion of the B/C class audio PA (if it's not in D class, I don't have explanation for it in this case). However, I don't have problems with Eco modes.
With regards, Pavel

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

Re: whoosh sound at ends of DMR transmissions

Post by G4EML » Sat Apr 24, 2021 9:14 pm

The noises with CC Filtering off are present on all radios as far as I know. They may be more noticeable on some than others, and it may also depend on the local RF noise levels.

The problem with the audio amp when the battery is fully charged is a hardware problem. See Jason's web page for a fix.

http://members.optuszoo.com.au/jason.re ... 77mods.htm

olin.

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