SDRTrunk Conventional P25 (non-trunked)

[boonebroadcaster]

Good morning, working on getting a UHF P25 (non-trunked) channel setup and running into some issues. First the hardware- running SDRTrunk on a Mac w/ a RTL-SDR V3 dongle and a telescoping antenna. I pulled the frequency using the radio reference database feature, the frequency is 460.0625. I have adjusted the Gain Control Master to Max (for testing). I am only getting about a 10th of the transmissions to come through. I have a capable p25 radio sitting right next to me, so I can hear through the radio that I am missing through the sdr app.

One thing I am curious about is on the tuners menu the frequency is different than what I have set (see photo below). The frequency shows 460.0375 instead of what is programmed in the playlist (460.0625). Any help would be greatly appreciated! I have watched numerous youtube videos on setting up SDRTrunk, however most talk about trunked systems, and this system is a conventional p25, non-trunked system. Any help would be greatly appreciated!

 

[boonebroadcaster]

Is there a need for two RTL-SDR dongles for a conventional P25 frequency? I see lots of posts about needing two, but I think that would just be for a trunked system to monitor the control and talking channels, correct?

 

[Enforcer52]

Is there a need for two RTL-SDR dongles for a conventional P25 frequency? I see lots of posts about needing two, but I think that would just be for a trunked system to monitor the control and talking channels, correct?

You only need 1 sdr for a conventional p25 system. I run 11 channels on one sdr, of which 6 are p25 channels.

The frequency showing in the Tuners tab is the center frequency for the sdr when it is in idle mode.

You probably need to adjust the PPM up or down till you get the best reception, do this a little at a time till you get close then the sdr should adjust automatically as long as you leave the Enable Tuner to Auto Adjust ticked on.

 

[dave3825]

If the conventional freqs fit inside the dongles reach, you need one dongle. If the freqs span more than the dongles reach, usually 2.4mhz, then you would need more dongle. Your pic shows the same 460 freq two times, and a 453 freq, To do both, you would need an additional dongle. As mentioned, freq listed in tuners is the center point so you sould be able to receive 1.2mhz up and 1.2mhz down from that freq.

Looks as if KSP could be going to a new trunked system at some point.

I have adjusted the Gain Control Master to Max (for testing).

Never a good idea. Bump it all the way down. Bump up until signal peaks highest point, and noise floor just starts to rise, then back it off a hair.

I am only getting about a 10th of the transmissions to come through. I have a capable p25 radio sitting right next to me, so I can hear through the radio that I am missing through the sdr app.

You have a p25 radio with what antenna? And what antenna is the dongle using?

 

[boonebroadcaster]

You only need 1 sdr for a conventional p25 system. I run 11 channels on one sdr, of which 6 are p25 channels.

The frequency showing in the Tuners tab is the center frequency for the sdr when it is in idle mode.

You probably need to adjust the PPM up or down till you get the best reception, do this a little at a time till you get close then the sdr should adjust automatically as long as you leave the Enable Tuner to Auto Adjust ticked on.

Thanks, you mention you are running 11 freq from one tuner. Are all of those within the bandwidth of the tuner, so in essence you can scan them?

 

[mtindor]

Thanks, you mention you are running 11 freq from one tuner. Are all of those within the bandwidth of the tuner, so in essence you can scan them?

Yes, of course. Otherwise he would not be able to listen to them all.

 

[Enforcer52]

Are all of those within the bandwidth of the tuner

Yes the are with the 2.4 range of the tuner, 11 is what I listen to and stream all the time, but acutualy there are 16 channels altogether with the vfire and vmed channels that are not used all the time.

 

[boonebroadcaster]

If the conventional freqs fit inside the dongles reach, you need one dongle. If the freqs span more than the dongles reach, usually 2.4mhz, then you would need more dongle. Your pic shows the same 460 freq two times, and a 453 freq, To do both, you would need an additional dongle. As mentioned, freq listed in tuners is the center point so you sould be able to receive 1.2mhz up and 1.2mhz down from that freq.

Looks as if KSP could be going to a new trunked system at some point.

View attachment 175440


Never a good idea. Bump it all the way down. Bump up until signal peaks highest point, and noise floor just starts to rise, then back it off a hair.



You have a p25 radio with what antenna? And what antenna is the dongle using?

I am using a telescoping antenna. I was using the smaller M6 (black, no blue rings), however I didn't have any luck with that one. I am now getting reception with proper placement, it appears. I'm a bit confused on your description of how to adjust the gain settings? The noise floor, I am assuming is green on the waterfall? How do I "bump up until signal peaks highest point and noise floor starts to rise"? There isn't a control channel, so should I continue to monitor and adjust when a tx is taking place? Thanks for the help!
Correct KSP is transitioning to a trunked system, however they started on the western side of the state, and it will still take several years before it is up and running in the eastern side of state.

 

[Enforcer52]

An outside antenna will give the best reception, and if you are anywhere near forested or hilly land it is pretty well required. I would think this is part of the problem with the missed transmissions you mentioned.

Yes make tiny adjustments to your gain when there are transmissions on the channel, also on the PPM. Once it is close, PPM will auto adjust to best point over a little time if auto adjust left on.

 

[dave3825]

You want to take your gain off automatic and look at the spectrum. Start increasing the gain until the signal reaches its highest point, without the noise floor rising too much.

Low gain, Low noise floor, No signal present.




Higher gain, signal present, Noise floor still low.