SFPD Radio system

kf6mxk

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I just got a call from my nephew who is a motorcycle cop with the SFPD . I asked about their radio's . He stated that half the time you can't understand what is being said. It looks like encryption is not working.
 

nokoa3116

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The P25 audio that is now used on top of encryption in SF sounds very different than what analog sounded like in their Motorola Type 2 system. But it doesn't have to do with encryption. It's using a digital vocoder, that is designed to process voice. It compresses the audio. The modern systems today that use P25 often utilize TDMA (P25 Phase 2) that essentially places 2 voice channels in the same bandwidth where there was just 1 before. It takes sometime to get used to it, and often some names of streets and such can be difficult to understand. After years of listening to it though, I got used to it and understand it quite well. So do many people all over the world. It's just a learning curve. It has its flaws, but also have pros.
 

spencerwww

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I just got a call from my nephew who is a motorcycle cop with the SFPD . I asked about their radio's . He stated that half the time you can't understand what is being said. It looks like encryption is not working.
Is everything encrypted or just police no fire ems hospital eta
 

rustyhodge

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Not everything is encrypted, including most police dispatch, EMS and Fire.
The digital vocoder they use for the new system takes a LOT of getting used to.
 

ECPD279

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Even without encryption, our radios on the EBRCS system lost a lot of sound quality when the system started using TDMA. The audio is now very tinny and overmodulated, making it difficult to understand on many occasions. For such a supposedly high quality radio system, I continue to be unimpressed. Perhaps the issues on the SF TDMA system are similar.
 

nokoa3116

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Even without encryption, our radios on the EBRCS system lost a lot of sound quality when the system started using TDMA. The audio is now very tinny and overmodulated, making it difficult to understand on many occasions. For such a supposedly high quality radio system, I continue to be unimpressed. Perhaps the issues on the SF TDMA system are similar.
Yeah it’s unfortunate. TDMA on P25 uses the AMBE vocoder which is about half the bitrate of what it was previously on FDMA (phase 1) which used the IMBE vocoder. I noticed also that the phase 1 voice could have much more errors and still sound okay. Versus on phase 2 with AMBE, where you get a little bit of errors then it’s just silent.
 

rustyhodge

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I was watching the public hearing on last week's OIS, and they included a bunch of the radio traffic. This will give you an indication on how the radio system should sound on the radios that they're using, vs the sound on scanners most of us use:


(Jumps right to the radio traffic part)

Sounds a lot clearer than both my BCD996p2 and the Bluetail p25rx. (As both those are reverse-engineered on the protocols). I suspect that it might have to do with some companding and preemphasis being used in front of the codec/vocoder, but that's just a wild guess. (The compander would explain some of the very different voice levels).
 

nokoa3116

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I was watching the public hearing on last week's OIS, and they included a bunch of the radio traffic. This will give you an indication on how the radio system should sound on the radios that they're using, vs the sound on scanners most of us use:


(Jumps right to the radio traffic part)

Sounds a lot clearer than both my BCD996p2 and the Bluetail p25rx. (As both those are reverse-engineered on the protocols). I suspect that it might have to do with some companding and preemphasis being used in front of the codec/vocoder, but that's just a wild guess. (The compander would explain some of the very different voice levels).
Hmm that does not sound very good. Something about the voices is not very intelligible. It's not completely horrible, but my regularly monitored P25 Phase 2 systems, such as SVRCS, sound better.
 
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nokoa3116

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Hmm that does not sound very good. Something about the voices is not very intelligible. It's not completely horrible, but my regularly monitored P25 Phase 2 systems, such as SVRCS, sound better.
I actually went to the Vimeo video and it sounded better there. Watched the body cams where their radios are heard, and they sound pretty normal. Didn't notice any garble, or what not. I still think some of the other p2 systems I monitor do sound louder, and clearer.
 
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