Nooelec SMArt XTR issues

[MCWKen]

I recently purchased a Nooelect SMArt XTR, and in a previous post about OP25, found that it did not decode Trunked control channels. A suggestion was made to play with the frequency offset in hopes there was enough of a signal to work with. That was not the case. In the thinking it was perhaps defective, I ordered another. It performs the same way. In addition, I also purchased a Nooelect LaNA in hopes that with the XTR would improve the situation. I will provide scopes for both the old SMArt and new XTR and let the group perhaps offer solutions. The file names describe each case and configuration. The plots are from two different sites, DeWitt and Muscatine, Iowa.

 

[imonitorit]

Double check BW and signal strength. I wouldn't crank the gain all the way up, you also are bringing up the noise floor.

 

[dave3825]

That one looks the best. It does show the PPM (offset) being a little off but It should decode but it decode better if its directly on frequency (centered) . And there is to much bandwidth selected. You want closer to the black lines as to much and you pulling in some noise with the signal.

 

[MCWKen]

I must apologize, but have not gotten time to experiment and post this.

Using OP25, I put the XTR in line, using a site 2 miles away, offset the tuning going step by step first up to 20,000 hz then down 20,000 hz, but the software could not decode the control channel, as you see below (0 tsbks). Then, I set the gain LNA down to 20, but got the same result offsetting +/- 20,000 hz. I went to 3 other sites using the XTR, and the results were the same, no decoding of the control channel. The second image is from a tuning program called GQRX, again using the local site. The bandwidth shown is only to zoom in on the center frequency to illustrate the loss of signal at the center.

 

[dickie757]

Like Dave said, narrow up your receive bandwidth. It looks like you are twice as wide as should be. Your SNR will be out of whack.

 

[MCWKen]

Like Dave said, narrow up your receive bandwidth. It looks like you are twice as wide as should be. Your SNR will be out of whack.

This is not the actual program that is decoding. It is just a tuning program. I used it only to illustrate what the signal looks like using the XTR. The decoding program, OP25 automatically adjusts the frequency error, and also offsets the fine tune as needed. As I had previously had shown, I had manually offset +/- 20,000 hz without any decoding.

 

[dave3825]

This is not the actual program that is decoding. It is just a tuning program. I used it only to illustrate what the signal looks like using the XTR. The decoding program, OP25 automatically adjusts the frequency error, and also offsets the fine tune as needed.

Yes, that’s gqrx, which is the Linux equivalent of sdr# for windows. Many use it as as a receiver and also to determine gain and ppm settings. I am slightly rusty on op25 as mine runs headless and I have not had to mess with it quite some time. I do know that correct gain and offset need to be defined in op25 to get up and running. While there may be an auto tune, it’s best to have it set as close as possible.

What we are saying is too wide in the shot is the bandwidth. I don’t remember if there is a setting for that but between 9.5 and 12.5 should work. It’s also most likely defined in hertz.

Looking at your op25 pic, the offset is off.



As far as gain, when in gqrx, start with the gain low, and raise and watch the signal peak. You ideally eat it at its highest right where the noise floor starts to rise. Then back off a hair and obtain that gain value and use it in op25.

 

[MCWKen]

Yes, that’s gqrx, which is the Linux equivalent of sdr# for windows. Many use it as as a receiver and also to determine gain and ppm settings. I am slightly rusty on op25 as mine runs headless and I have not had to mess with it quite some time. I do know that correct gain and offset need to be defined in op25 to get up and running. While there may be an auto tune, it’s best to have it set as close as possible.

What we are saying is too wide in the shot is the bandwidth. I don’t remember if there is a setting for that but between 9.5 and 12.5 should work. It’s also most likely defined in hertz.

Looking at your op25 pic, the offset is off.

View attachment 172799

As far as gain, when in gqrx, start with the gain low, and raise and watch the signal peak. You ideally eat it at its highest right where the noise floor starts to rise. Then back off a hair and obtain that gain value and use it in op25.

The second image in your post was after manually offsetting in steps of 100 hz at a time up to 20 khz in either direction. At no time in all those steps did OP25 decode any blocks. I even set LNA to 10, and yet no decoding. As far as bandwith, I am not sure there is a setting in OP25 for that.

I do thank everyone for their input, but I have spent over 10 hours trying to debug this. I ordered the normal SMArt again. If anyone wants a free XTR, contact me, it does not serve my needs.

Regards,
Ken Schmidt

 

[dave3825]

Hang into the xtr before ditching it and see what happens with the smart. Are you Linux only?

I’m going to look at mine over the weekend. Sometimes too much gain can cause issues.

 

[MCWKen]

I am Linunx only. And have used the SMArt before, and it worked fine. I was thinking the XTR was an upgrade.