396XT Speaker Noise

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pks
Posts: 101
Joined: Wed Aug 13, 2008 12:26 pm

396XT Speaker Noise

Post by pks » Fri Jan 20, 2012 12:17 pm

Has anyone noticed a short burst of noise from the speaker right after a keytone while listening to P25 transmissions? For eg, during a P25 transmission, if I press any key to cause a beep from the speaker, I would hear a short burst of noise right after the beep. This also happens after the beep of low battery. Anyone else experienced this?
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commsmc
Posts: 73
Joined: Wed Nov 18, 2009 11:14 pm

Re: 396XT Speaker Noise

Post by commsmc » Tue Feb 14, 2012 12:03 pm

I have noticed this recently, it's quite annoying. Sounds something like 'psssst'. I think it only occurs when there is P25 audio being decoded and a 'beep' comes through...

Mike
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Bigfella237
Posts: 1897
Joined: Fri Feb 26, 2010 3:11 pm
Location: In geosynchronous orbit above the Far South Coast of NSW, Australia

Re: 396XT Speaker Noise

Post by Bigfella237 » Tue Feb 14, 2012 12:36 pm

Sounds to me like DSP is being stopped to allow the beep to have full use of the speaker, then takes a fraction of a second for processing to restart?

Andrew
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citabria
Site Admin
Posts: 1064
Joined: Thu Aug 14, 2008 8:22 pm

Re: 396XT Speaker Noise

Post by citabria » Tue Feb 14, 2012 3:45 pm

P25 only sends its frame sync every 180ms during a voice transmission, so if the scanner stops and loses sync (ie, its busy playing a beep or whatever) then it can take up to 180ms before a frame sync is sent again. The frams sync is what the radio uses to identify a P25 transmission, so until this is sent, the radio treats the transmission as FM.
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