Helicopter background TX noise in DMR mode

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fapuc
Posts: 3
Joined: Sat Nov 21, 2020 12:49 pm

Helicopter background TX noise in DMR mode

Post by fapuc » Sat Nov 21, 2020 1:02 pm

Good morning,
problem with Baofeng DM5RPLUS
in DMR correspondents hear background noise like helicopter blades, it seems the fast switching unfiltered slots. It doesn't happen in analog FM and not even with original firmware.
Regards
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kt4lh
Posts: 151
Joined: Sun Jan 12, 2020 4:27 am

Re: Helicopter background TX noise in DMR mode

Post by kt4lh » Sat Nov 21, 2020 2:28 pm

If you're using an external hand mic, that's common, and unlikely it would matter if it was the original firmware or OpenGD77. If you're not using a handmic, odd, never heard of this (typically called 'motor boating' from the noise) just using the HT directly.

VK3KYY
Posts: 3200
Joined: Sat Nov 16, 2019 3:25 am
Location: Melbourne, Australia
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Re: Helicopter background TX noise in DMR mode

Post by VK3KYY » Sat Nov 21, 2020 11:13 pm

This does seem to happen on some radios.

But we have no idea why it happens.

Possibly these radios have hardware fault, and some difference in the way the official firmware samples the audio means the official firmware doesn't have this problem

fapuc
Posts: 3
Joined: Sat Nov 21, 2020 12:49 pm

Re: Helicopter background TX noise in DMR mode

Post by fapuc » Sun Nov 22, 2020 12:32 pm

Yes, the official firmware doesn't have this problem,
and it does not depend on radiofrequency reentry, because it is also tested with 50 mW and resitive load as an antenna, with HotSpot.
Regards

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EB3AM
Posts: 192
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Location: Catalonia, not Spain
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Re: Helicopter background TX noise in DMR mode

Post by EB3AM » Thu Nov 26, 2020 8:49 am

I have an original radioditty microphone, which does this effect. The problem is not with the device and less with the firmware.
The problem is the poor quality of the microphone that picks up the TDMA modulated rf, which makes a pulsating effect. If you decrease the power the effect is attenuated.

Don’t blame the radio, and the firmware.
Jordi, EB3AM, Talarn JN02ke, Catalonia.

Radios: OpenGD77 RadioDitty, Icom 7300, mcHF clone QRP,
Repeaters: MMDVM with a Standard RP80-U (DMR + FM), MMDVM + Motorolas (DMR+FM), Hytera UHF DMR+FM repeater.

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