DSDPlus PPM correction

[mtindor]

You are probably right. I think the main problem I have with them is that the filters aren't narrow enough. I can sit on the middle frequency of three that are spaced at 12.5 kHz and DSDPlus decodes all three of them. Site numbers and color codes just bounce around.

That's ludicrious. Press the "B" when focused on FMP24 and set your bandwidth accordingly.

NDN48: 4.0
NEXEDGE96/DMR: 7.6
P25: 9.5 or 12.5

I've sat on 454 band with huge signals (many) within 454.0 and 454.1 and have never had DSDPlus copying them all and switching between them.

Sure, there could be some difficulty if somethin is on 454.600 and then a another running on 454.60625. But you said signals were spaced 12.5 khz apart. That can easily be handled by setting the appropriate bandwidth.

 

[prcguy]

If you’re tweaking a receiver, any receiver on frequency, use the highest frequency possible for the alignment. I like to use a TV station and tune to the ATSC pilot frequency as most TV transmitters are locked to a ver good frequency standard. For example, if you have TV channel 20 in your area the ATSC pilot frequency would be 506.31MHz.

 

[dlwtrunked]

If you’re tweaking a receiver, any receiver on frequency, use the highest frequency possible for the alignment. I like to use a TV station and tune to the ATSC pilot frequency as most TV transmitters are locked to a ver good frequency standard. For example, if you have TV channel 20 in your area the ATSC pilot frequency would be 506.31MHz.

And be aware that the newer ATSC-3 (NextGen) signal many stations are changing to do not have a pilot. In addition there is no specified tolerance for the older ATSC 1.0 pilot that does have a pilot *ideally* at 0.309411..kHz above its low end--some are GPS disciplined and very accurate and some not and I have seen some very noticeably off frequency (10's of Hz) with a calibrated better than 1 Hz spectrum analyzer. Finally, be aware that the design of almost all SDRs does not allow them to be as accurate as you would wish as their internal design is in step. When people think they have calibrated to dead on accurate, it is a good bet that it really is not no matter how they calibrated. I use a Signal Hound with a GPSDO and have many SDRs (Airspy, SDRPplay, RTL-SDR). Even GPS discpining an AIRSpy R2 does not change this fact --but does make it more stable. No matter how you calibrate them, you will not get dead on accurate--just closer than you might have been otherwise. After a while, when one knows this, spending a lot of time on "calibration" is really a wast of time.

 

[dlwtrunked]

And be aware that the newer ATSC-3 (NextGen) signal many stations are changing to do not have a pilot. In addition there is no specified tolerance for the older ATSC 1.0 pilot that does have a pilot *ideally* at 0.309411..kHz above its low end--some are GPS disciplined and very accurate and some not and I have seen some very noticeably off frequency (10's of Hz) with a calibrated better than 1 Hz spectrum analyzer. Finally, be aware that the design of almost all SDRs does not allow them to be as accurate as you would wish as their internal design is in step. When people think they have calibrated to dead on accurate, it is a good bet that it really is not no matter how they calibrated. I use a Signal Hound with a GPSDO and have many SDRs (Airspy, SDRPplay, RTL-SDR). Even GPS discpining an AIRSpy R2 does not change this fact --but does make it more stable. No matter how you calibrate them, you will not get dead on accurate--just closer than you might have been otherwise. After a while, when one knows this, spending a lot of time on "calibration" is really a wast of time.

"0.309411..kHz" was meant to be "0.309411 MHz" or "309.411 kHz".