Audio Breakup on P25 in Fairfax County
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TOPIC: Audio Breakup on P25 in Fairfax County

Audio Breakup on P25 in Fairfax County 07 Sep 2012 19:18 #10157

  • captainkoala
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Hi All,
I have owned an HP for a little under a year and from the beginning I have had trouble with audio breakup. It is intermittent and sounds like a muting of the signal rather than the beeps and chirps of weak signal. It is only the P25 and not analog. The unit was sent back to Uniden twice for repair and the second time they replaced it with a factory repaired unit. The replacement is showing the same symptoms. I have tried everything. I have opened the squelch, tried attn on and off, AGC on and off, the supplied antenna, outdoor antenna, today I climbed on top of my house and used the supplied antenna. I had all four bars lit full time and yet I still had the breakup. My BC-796D does not have this problem. The only reason I am replacing the 796 is so I can receive STARS. Does anyone have any idea what is going on?

Re: Audio Breakup on P25 in Fairfax County 09 Sep 2012 10:04 #10159

  • JD3
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blog.tcomeng.com/wp-content/uploads/2007/12/The-Great-APCO-Project-25-Boondoggle-Feb-2011.pdf

Multipath signal distortion.

You have multiple transmitter sites, and are receiving signals from more than one source.
Sometimes one is louder than another, and not always the same transmitter being heard.

Re: Audio Breakup on P25 in Fairfax County 09 Sep 2012 17:31 #10162

  • captainkoala
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Hi JD3,
Thanks for the information. I have considered multipath in relation to reflected signals rather than multiple transmitter sites. I am fairly close to one of the sites in the system and have been able on occasion to hear another site. However, it is really weak and the attenuator takes it out. What I find most perplexing is the fact that my BC-796D works perfectly. I have even tried the stock antenna from the 796 on the HP with no improvement.

Re: Audio Breakup on P25 in Fairfax County 09 Sep 2012 18:17 #10164

  • JD3
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What external antennas have you tried?
Are the audio problems with every signal received?
What percentage (estimate) of transmissions received garbled?

I experience the same type of transmission breakup here in Wisconsin.
I live 2 miles or so away from one of the main transmitter sites.
Once in a while, never consistent, the audio is distorted.
I also noticed it is more of a problem when I have the volume set at max.
When I turn the volume down a couple steps from max the problem almost goes away.
It seems like the internal speaker is being over driven and distorting?

I asked a fellow ham about this and was told it might be the scanner is not decoding the signal exactly like the commercial equipment being used.

I also googled a search on P25 problems and a host of other stuff came up.

Possible encryption issues, background noise in the microphone of the originating radio transmission (digital conversion doesn't like noise) or the system is experiencing heavy usage.

That was one problem the firefighters were having on our new system. Whenever the firefighter transmitted near a fire truck, all the engine noise was garbling the transmission. The tech's quickly learned to switch to noise canceling mics.

If the problem is sporadic, and most of the time the scanner works fine, I would not worry. That has been a problem of P25 since day one, and a lot of time by radio technicians is spent trying to remove these problems from the system for its normal users, the police and firefighters.
Last Edit: 09 Sep 2012 18:41 by JD3.

Re: Audio Breakup on P25 in Fairfax County 09 Sep 2012 18:23 #10165

  • JD3
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wiki.radioreference.com/index.php/P25_audio_decode_level_adjustment

Also found this on radio reference.com -
Maybe because the HP-1 doesn't allow you adjust audio decode levels?

I do not have the extreme upgrade, it might help to have that.
In the extreme upgrade there are a few features to try:
trunked system analyzer - monitor system load, reception status, and activities
band scope - locate interference? possible birdie or harmonic from amateur radio transmission?
RF power plot - look at antenna performance, direction finding
Last Edit: 09 Sep 2012 18:33 by JD3.

Re: Audio Breakup on P25 in Fairfax County 10 Sep 2012 13:17 #10166

  • KD8HE
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This happens even with the commercial systems. P25 systems I monitor have difficulty on occasion, especially when talking to a mobile unit.
RF path distortions of any type will confuse the Digital to Analog conversion and result in all kinds of wierd sounds. The professional communicators frequently ask "repeat your traffic you went digital" and on occasion I hear them clearly when the agency base does not.
Considering all the factors there is not much you can do to achieve consistency and you eventually get used to it.
Harry
Ham OP since 1981
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