SDRTrunk - Fine Tuning

[K0MSM]

Greetings all -

My county has gone digital/P25, and I don't want to assign my SDS-200 to Broadcastify duty. (My PRO-2096 was doing this just fine until they went completely P25.) So, I'm looking at SDRTrunk to handle this function.

I've got SDRTrunk installed, and I'm fully aware of the concepts of SDR and trunking. I've also been looking over the docs in the SDRTrunk Wiki. But, I do have a few questions that I hope some of you SDRTrunk gurus out there might be able to assist a n00b with. (Bonus points if you're in Iowa and familiar with ISICS.)

(For the record, I'm using SDRTrunk on a Win10 machine right now, with a NooElec E4000 dongle that I've had for like, almost 10 years now maybe?)

1) I know I need to calibrate the dongle in SDRTrunk before I try to use it. So, I've done that. Using what I'm about 99% sure is the audio for my local system, I've adjusted the PPM to where the waterfall is now just about dead-on center of that audio. I had to set it to 318.5 - seems like a lot, but maybe that's normal?

2) Shouldn't I also see something showing on the waterfall for the control channel? I see nothing there. Nice thing is, for my local system, there are only 2 frequencies. Either can be audio or control at any given time.

3) Once I get everything set up, in my "Now Playing" window (I believe it is), even when the SDS is picking up traffic on the system, and the waterfall is showing activity on the frequency, SDRTrunk shows "idle." And, I'm assuming this is why I'm also not getting any audio on the PC's speakers. When I do a test tone in User Settings, I hear THAT tone fine, so I know SDRTrunk can talk to the speakers OK.

I'm doing the import directly from RadioReference, so I know my settings for frequency and talkgroups are good. Plus, those are the same as what I'm using on my SDS.

I feel like I'm almost there... just need a little tweaking, and I'll be cooking with gas.

Thank you!

Sean

 

[dkcorlfla]

I'm not running SDRtrunk so I'm not sure about this but can it tune NOAA weather (162.4 > 162.55Mhz)?

I often use the NOAA broadcast to help fine tune other SDR software. Helps get the gain and PPM setup fast.

Might have to fine tune a bit when you move up to the P25 you want to scan but it should get you in the ballpark.

 

[dave3825]

Did you start the channel? Post picks showing the dongle tuned to the control channel.

 

[Boingel331]

The channel menu is where I find how much PPM adjustment is needed. The circled PLL number is the most precise indicator of that (the closer to 0, the better).

Gain is equally important. I like to have an RSSI of around -20db.

 

[dave3825]

Your in the wrong spot and do not have the channel started. (running)

First, start the channel in the playlist editor, so you screen looks like this





then click the tuners tab and post a pic like this

 

[K0MSM]

Did you start the channel? Post picks showing the dongle tuned to the control channel.

Hi Dave - thank you for the response! Here are my pics:


The frequency in red is currently the audio. Circled in yellow is where I would expect the control channel to be.



Here is my channel information.



And here is my alias information.



And last but not least, my Tuners page.

Sean

 

[dave3825]

I would go into the tuner tab and take the gain off of auto and play around with the values in there. Auto is horrible and your not getting a strong enough signal for the control channel to lock. Where it says idle, it will change to control once its getting a better signal..

 

[dlwtrunked]

No over the air signal except an accurate on frequency quite carrier is actually good for calibration (NOAA weather does not meet that criteria). Otherwise, even better, much better, is to use harmonics of a 10 MHz GPS disciplined oscillator ($100-$200) Best thing is an ATSC 1.0 pilot if that pilot is GPS disciplined (such pilots have no tolerance and may be half or so are not accurate per the published ATSC 1.specification). (And ATSC 1.0 are gradually being replace by ATSC 3 which do not have a pilot.) But even then, most cheap SDR tune internally in steps that defeat such accurate calibration (they cannot finely resolve frequencies). I have looked carefully at this and can tell you that those who think they are dead-on accurate have fooled themselves. this whole subject is more complicated than most think.
Finally, here is a look (using long term averaging), using an accuracy of about 1 Hz of measured NOAA frequencies with the error at the time here:
162.399926 (NWS) -74 Hz
162.424966 (NWS) -34 Hz
162.450015 (NWS) +15 Hz
162.474885 (NWS) -115 Hz
162.500001 (NWS) 1 Hz
162.549948 (NWS) -52 Hz
So those themselves were sometimes almost 1ppm off and elsewhere one might find worse. The net result is do not mess with calibrating unless it is really off or you actually have a proper signal and understand the limitation of what the calibration actually does.

 

[K0MSM]

I would go into the tuner tab and take the gain off of auto and play around with the values in there. Auto is horrible and your not getting a strong enough signal for the control channel to lock. Where it says idle, it will change to control once its getting a better signal..

I've tried various settings since taking it off auto. I still can't seem to get a good lock on the control frequency. (And I still don't see it on the waterfall.)

Sean

 

[K0MSM]

No over the air signal except an accurate on frequency quite carrier is actually good for calibration (NOAA weather does not meet that criteria). Otherwise, even better, much better, is to use harmonics of a 10 MHz GPS disciplined oscillator ($100-$200) Best thing is an ATSC 1.0 pilot if that pilot is GPS disciplined (such pilots have no tolerance and may be half or so are not accurate per the published ATSC 1.specification). (And ATSC 1.0 are gradually being replace by ATSC 3 which do not have a pilot.) But even then, most cheap SDR tune internally in steps that defeat such accurate calibration (they cannot finely resolve frequencies). I have looked carefully at this and can tell you that those who think they are dead-on accurate have fooled themselves. this whole subject is more complicated than most think.
Finally, here is a look (using long term averaging), using an accuracy of about 1 Hz of measured NOAA frequencies with the error at the time here:
162.399926 (NWS) -74 Hz
162.424966 (NWS) -34 Hz
162.450015 (NWS) +15 Hz
162.474885 (NWS) -115 Hz
162.500001 (NWS) 1 Hz
162.549948 (NWS) -52 Hz
So those themselves were sometimes almost 1ppm off and elsewhere one might find worse. The net result is do not mess with calibrating unless it is really off or you actually have a proper signal and understand the limitation of what the calibration actually does.

When I started up the software, the waterfall was showing the audio frequency way off from where I would have expected it to be. I could remove the "correction" I suppose, and see what happens. But at least, at the moment anyway, the audio is showing up more or less where it's listed in the RRDB. SDRTrunk just isn't locking on to a control signal. (And I don't see that in the waterfall either.)

Sean

 

[dave3825]

When you use that dongle in other software (sdr# or sdr++) and tune to a local freq, what do you need to set the PPM to?

 

[dave3825]

Is there another site near Greene County? The 2 red are what you have programmed for that site. Any idea what the 2 yellow are?

 

[K0MSM]

Is there another site near Greene County? The 2 red are what you have programmed for that site. Any idea what the 2 yellow are?


View attachment 181603

Oh, there's a lot around us. We're surrounded by 6 other counties, all on ISICS as well. So that's probably one of them. I've tried setting up two other counties, with the same results - nothing gets locked on.

For your earlier request, I fired up SDR Console. I have a nice strong signal at 772.56875, which I would expect. And, with no correction on the dongle. (BTW, there is no correction down on VHF, either. If I point the dongle at 162.55, I get the WX channel at 162.55.) But I get nothing on 771.76875 - what appears to be the audio is showing up at 771.47 (roughly).

I'm quite... confused.

Sean

 

[K0MSM]

FYI - here's what I'm seeing:

What I'm figuring is the control, right where I'm expecting it. It never changes.


What appears to be the audio... I expect it where the green bar is. It's off by a little bit. (There's only a signal there when someone transmits.)

And, there is no other signal that is off by that much up where the control is. That would be too easy, right?

Sean

 

[dave3825]

So then the dongle is pretty close if you don't need to set ppm. What antenna are you using and where is that?

 

[K0MSM]

So then the dongle is pretty close if you don't need to set ppm. What antenna are you using and where is that?

Discone at about 15' AGL. Same antenna I use for my SDS 200.

Sean

 

[K0MSM]

So then the dongle is pretty close if you don't need to set ppm. What antenna are you using and where is that?

You'd think, based on what the control looks like. But the other frequency is way off. Like 320 KHz or so.

Sean

 

[dave3825]

Discone at about 15' AGL. Same antenna I use for my SDS 200.

Does the 200 lock onto that site? And how far are you from the site and how are you splitting the antenna?

You'd think, based on what the control looks like. But the other frequency is way off. Like 320 KHz or so.

You mean this one off?

 

[K0MSM]

Maybe it's a bad dongle. Don't know. I've ordered a new one (seeing as this one is about 10 years old, and I'm sure things have changed since then). Interesting to note, that while RRDB 771.76875 as one of my county's frequencies, the SDS-200 shows that it's actually picking up on 771.46875. (And it's using the other frequency of 772.56875.)

So, I reset everything in SDRTrunk and started over in the tuner. Now, I'm actually on two signals that look like they *could* be what I'm seeking to track:

Red is audio, yellow is control. This is also being accomplished with a PPM of -70 now, instead of -319 (or whatever I had before).

Still - there is nothing to lock onto, apparently.

This has been about 3 hours or so of frustration. I'm not sure what else to try at this point, other than a new SDR. Maybe this one is just a POS. Dunno. Ordered a new V5 from Amazon just now. Will be here on the 15th.

Sean

 

[K0MSM]

Does the 200 lock onto that site? And how far are you from the site and how are you splitting the antenna?




You mean this one off?

View attachment 181614

The SDS-200 locks on with zero problems. I'm about 10 miles away as the crow flies, and I'm also able to lock onto sites in all of the counties around me on the 200.

The antenna comes in and I'm currently splitting it off with a BNC T-connector.

Sean