Unable to source channel from preferred tuner

[Stephen Leander]

I posted this on the Facebook group, thought I'd try here as well.  I upgraded to the 0.6.1-Beta 1 code over the weekend, and I am getting these messages on the console:

 INFO  i.g.d.s.t.m.TunerManager - Unable to source channel [1596053540] from preferred tuner [Airspy 62CC68FF-352A7D5B] - searching for another tuner  [240MB/912MB 26%]

My setup is a single Airspy tuner running at 10MHz, monitoring an 18 channel P25 Phase 1 simulcast cell that spans 7.1375Mhz (851.875 - 859.0125MHz).  I noted the tuner jumping around, mostly between 852.xx and 854.xx, and realized it might be an issue receiving the higher channels when it was down at 852, so I setup 2 NBFM decoders - one at 851MHz and one at 859Mhz that load before the P25 decoder (Facebook suggestion). That seems to have stabilized the jumping around, but I still am getting the "Unable to source channel" error.

Any ideas?

Thanks!

Stephen Leander

[dave38...@gmail.com]

Figure out the center freq for that spread and create a dummy channel for it. Then the dongle will go 3.56 up and down from the center giving you the 7.1375  tho I am away from my pc and not sure of the exact usable range when running 10mhz.  You might have to play with the dummy freq depending where control channels are. 

[Stephen Leander]

That's what I did with the 2 NFMB decoders - bracket the system channels so the tuner doesn't move off, but I still get the error.  A single dummy channel can still allow the tuner to move up or down. 

[dave38...@gmail.com]

If you start the dummy channel first before the system, does it still do it? 

[Stephen Leander]

Yes.  Pic showing the 2 NBFM decoders running.

[charley....@gmail.com]

Airspy R2 has 8 MHz usable bandwidth.

[Stephen Leander]

I tightened up the high and low NBFM decoders to be 100KHz above and below the range of the site, which is 7.1375MHz wide from lowest to highest channel.  That fits inside an 8MHz window.  Hopefully, that'll help!

I do have another R2 I can add if needed, just need to get the appropriate cabling.  But at the bandwidth I thought the R2 was good for, it should have worked without the NBFM decoders to help bracket the site I am monitoring. As I am under 8MHz now, we'll see I guess!

Thanks!

Steve

[Stephen Leander]

Still have the error.  

2024-04-22 22:44:13.766 INFO  i.g.d.s.t.m.TunerManager - Unable to source channel [3273526070] from preferred tuner [Airspy 62CC68FF-352A7D5B] - searching for another tuner  [338MB/856MB 39%]
2024-04-22 22:44:13.877 INFO  i.g.d.s.t.m.TunerManager - Unable to source channel [3273581570] from preferred tuner [Airspy 62CC68FF-352A7D5B] - searching for another tuner  [554MB/856MB 64%]
2024-04-22 22:44:13.877 INFO  i.g.d.s.t.m.TunerManager - Unable to source channel [3273559070] from preferred tuner [Airspy 62CC68FF-352A7D5B] - searching for another tuner  [557MB/856MB 65%]

Steve

[dave38...@gmail.com]

 I setup 2 NBFM decoders - one at 851MHz and one at 859Mhz that load before the P25 decoder (Facebook suggestion).

So its 851.875 - 859.0125? 

I would try one dummy channel  set for 855.44375 which is the exact center. And if the R2 is truly giving 8mhz usable, it should do to 851.44375 to 859.44375. Start it first and verify your settings are still set to 10mhz. 

[dave38...@gmail.com]

Now that I have 2 eyes open, the freq its looking for (3.27352607 ghz) is not valid. 

 INFO  i.g.d.s.t.m.TunerManager - Unable to source channel [3273526070] from preferred tuner [Airspy 62CC68FF-352A7D5B] - searching for another tuner  [338MB/856MB 39%]

In any event, you would still need a dummy channel.

Here is someone else that had an issue where the tuner was trying to tune outside the limitations.

https://github.com/DSheirer/sdrtrunk/issues/1880

[Stephen Leander]

OK, it's not clear that the "channel" value is an actual frequency.  And yes, 3.2GHz is neither in the receiver's range, nor in the P25 systems range.  

So, reading the thread you linked, I'll have to capture some of the control channel's data it would appear. 

BTW, I have 3 dummy channels now, 100kHz above and below the range of the site/cell, and one in the middle.  They all load up before the P25 decoder.

Thanks for your help!  

Steve

[charley....@gmail.com]

It's possible that you are getting random poor decodes, leading to garbled channel number.  Your signal looks good; you could try reducing your gain incrementally to see if that helps with more reliable decoding.  What specific site / system are you trying to monitor?

[Stephen Leander]

It's monitoring a simulcast site on the Colorado DTRS, Zone 4 - site 28(dec) - Colorado Springs Simulcast.  I am actually the System Manager for the Zone, and we use this to stream feeds as requested by the talkgroup owners, as well as recording a few TGs.  We do have proper loggers for recordings that require it.  It's running at our radio shop in the City, and it's on a magmount antenna within a metal building - not the best.  We can fix, or move it - I used to host it at one of our RF subsites with no antenna on the receiver.  But easier to manage when it's sitting right here.  

Steve

[Stephen Leander]

I'll see about putting a high pass filter on the Airspy.  As we're the radio shop, the receiver might be getting clobbered by test transmissions 45MHz below.  The radios have front end filters - an Airspy doesn't (AFAIK).

[Stephen Leander]

Just an update, I found an old Celwave bandpass filter I was able to tune for the 851-859MHz frequencies of interest, it's inline with the receiver now, and I upped the gain a little bit on the receiver - seems clean so far (no errors), but it's only been about 60min.  While I didn't see any compression or other effects on the waterfall when key up a 3W handheld nearby without the filter (-45MHz offset), the filter provides about 50-60dB of attenuation at -45MHz, so it should help protect the reciever.  I did see the same errors in the middle of the night, so it probably has nothing to do with local system interference.  However, protecting the SDR from stuff outside what it needs to hear is just good practice anyway...

If I keep getting errors, I can try moving the setup to another site, or provide a raw recording of the control channel.  Thanks for your help!

Steve

[Stephen Leander]

Still getting errors, looked to record the control channel, but I don't see this option:  in the channel configuration editor, in the Recording tab at the bottom, turn on the control channel bistream record option and then start the channel.

This is what I see:

Steve