P25 Radios

General questions on scanning from 30 to 3000Mhz. Not sure what you can receive in your area? Here's the place to ask!

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numloxx
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P25 Radios

Post by numloxx »

Hi,

I'm trying to listen to some stations at the airport.
Their frequencies are 494.325 and 497.525, and they are P25. There is also another frequency 484.9375mhz, but I'm unsure if that is required.
The radios they use are Kenwood TK-5320's with a P25 label on the side.
I've created a P25 group according to the instructions on http://ozscan.blogspot.com.au/2011/12/u ... co-25.html and I can see the Signal Bar when somebody is transmitting but I cannot hear any audio. I've set a 400ms P25 Waiting time.

Any suggestions?

Comint
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Re: P25 Radios

Post by Comint »

numloxx wrote:I'm trying to listen to some stations at the airport.
Their frequencies are 494.325 and 497.525, and they are P25.
Probably should be 492.325 (Rpt Tx) and 497.525 (Rpt Rx)

There is also another frequency 484.9375mhz, but I'm unsure if that is required.
This appears to be an FM Simplex frequency.

I've created a P25 group according to the instructions on http://ozscan.blogspot.com.au/2011/12/u ... co-25.html and I can see the Signal Bar when somebody is transmitting but I cannot hear any audio.
It is more likely that this is P25 on a Conventional Repeater, so you would have to select One-Freq Trunk.

--
Comint

numloxx
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Re: P25 Radios

Post by numloxx »

Thanks for the tip.
I've put all 3 into seperate One-Freq trunks, and it seems to have done the trick.
497.525 seems to be the only active frequency though.
I'm guessing the other channel 492.325 is for Air BP use?
http://web.acma.gov.au/pls/radcom/licen ... NO=1966071
Haven't heard any activity on that channel yet though... but it is 5am on a Saturday morning lol.

rustynswrail
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Re: P25 Radios

Post by rustynswrail »

numloxx wrote:Thanks for the tip. I've put all 3 into seperate One-Freq trunks, and it seems to have done the trick. 497.525 seems to be the only active frequency though. I'm guessing the other channel 492.325 is for Air BP use? http://web.acma.gov.au/pls/radcom/licen ... NO=1966071 Haven't heard any activity on that channel yet though... but it is 5am on a Saturday morning lol.
For future reference, 497.5250 is the input to a repeater commonly called BRX or Base Receive, with 492.3250 as the output or BTX or Base Transmit. The split in this band is 5.2 MHz between repeater pairs.

Under normal circumstances listening to the repeater input means you are hearing those radios trying to access the repeater, ie 5 watt handhelds and 25 watt mobiles. Monitoring the output is the preferred option because the output is usually higher, but not always the case, (there are 5 and 15 watt repeaters throughout the band). An airport is an ideal place for a low power repeater, designed to cover only a small area.

Some users have repeater pairs assigned but only use either the input or output as a simplex assignment. It is more common practise to use the BTX or output, but the input can be also be used. Make sure the service you are trying to monitor is not using a repeater, but is in fact using their assignments as simplex.

R

numloxx
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Re: P25 Radios

Post by numloxx »

Thanks. Yeah 492.325 is the Output, as I can hear it in Maylands, where as when I'm at the airport, I can only head 497.525. Thank you! Hoping to still work out the Aerocare ramp radios next. But I think I will not have any luck as they are Motorola TRBO. Maybe the Uniden BCD436HP will do it?

rustynswrail
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Re: P25 Radios

Post by rustynswrail »

numloxx wrote:Thanks. Yeah 492.325 is the Output, as I can hear it in Maylands, where as when I'm at the airport, I can only head 497.525. Thank you! Hoping to still work out the Aerocare ramp radios next. But I think I will not have any luck as they are Motorola TRBO. Maybe the Uniden BCD436HP will do it?
Sorry to disappoint but the new Unidens are not capable of decoding TRBO (TDMA) or NXDN (FDMA) for that matter. They will do Phase II P25 and Phase I of course. Short of getting a TRBO radio and having the system admin program it for you, there is no way to monitor it. Having said that you can use a computer program known as DSD Decode, but I wish you luck. It works but is extremely touchy when it comes to setup and operation. Not to mention that walking around with a scanner and computer has it drawbacks.

Not being able to hear the output of the repeater at the airport is odd. Technically coverage should be superior, but not being able to hear or otherwise monitor the repeater makes it difficult to determine the cause.

R

numloxx
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Re: P25 Radios

Post by numloxx »

Thanks again.

I'm going to continue this in the MOTOTRBO thread, with some more findings.

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