SDS200

[Volfirefighter]

Is there a control channel decoder for Motorola P25 that will work with the SDS200 via the usb connection and NOT require a discriminator tap?

 

[maus92]

That capability could be enabled by a firmware update, and as of yet I have not seen any third party solution on the market. Probably easier to use an SDR dongle on a computer to run Unitrunker or similar software. I would not advise tearing into an SDS200. Not exactly sure what you want out of the cch signal, but a program like Proscan can log activity serially and provide a record and recordings.

 

[Volfirefighter]

So what is a good SDR dongle that will allow me to use Unitrunker to decode a 700/800 Mhz control channel? I should also note that it is a simulcast system.

 

[ka3jjz]

You should really ask this in the Software Define Radio forum, but I keep hearing of folks using utilities such as DSD and UniTrunker with the various RTL-SDR sticks....Mike

 

[maus92]

I own 5 of these:

Amazon.com: NooElec NESDR Smart v4 Bundle - Premium RTL-SDR w/Aluminum Enclosure, 0.5PPM TCXO, SMA Input & 3 Antennas. RTL2832U & R820T2-Based Software Defined Radio.: Computers & Accessories

Amazon.com: NooElec NESDR Smart v4 Bundle - Premium RTL-SDR w/Aluminum Enclosure, 0.5PPM TCXO, SMA Input & 3 Antennas. RTL2832U & R820T2-Based Software Defined Radio.: Computers & Accessories

www.amazon.com

One of these:

Amazon.com: RTL-SDR Blog V3 R820T2 RTL2832U 1PPM TCXO HF Bias Tee SMA Software Defined Radio with Dipole Antenna Kit: Electronics

Buy RTL-SDR Blog V3 R820T2 RTL2832U 1PPM TCXO HF Bias Tee SMA Software Defined Radio with Dipole Antenna Kit: Radio Antennas - Amazon.com ✓ FREE DELIVERY possible on eligible purchases

www.amazon.com

I prefer the Nooelec over the rtl-sdr. Both are stable TCXO (important feature,) but I find that the Nooelec take less freq correction, which is done in software. You only need one sdr, unless you want to go crazy and decode multiple control channels / systems.

Simulcast is not a huge factor when receiving / decoding a control channel, unlike P25 voice channels. The error correction in the cch signalling mitigates interference fairly well.

If I wasn't clear, Proscan will work with the SDS200 via USB or ethernet. But it is not really a control channel decoding program.

 

[slicerwizard]

So what is a good SDR dongle that will allow me to use Unitrunker to decode a 700/800 Mhz control channel? I should also note that it is a simulcast system.

The orange FlightAware Pro Sticks are good for UHF monitoring and very good for 700/800/900 MHz monitoring. They're far more sensitive than other dongles.

Pro Stick® and Pro Stick® Plus - FlightAware's USB ADS-B and MLAT receiver - FlightAware

FlightAware Pro Stick® and Pro Stick® Plus - High Performance USB SDR ADS-B Receivers

flightaware.com

 

[maus92]

I own a FlightStick Orange, however I haven't noticed that they are any better than the ones I mentioned - but then again, they are not any worse either. I already have amplification in my antenna system, so that might have something to do with it. I don't like the fact that the FlightAware case is plastic whereas the others use a metal case as a heat sink and presumably shielding. However, I'm sure a FA dongle would be fine.

 

[slicerwizard]

I own a FlightStick Orange, however I haven't noticed that they are any better than the ones I mentioned - but then again, they are not any worse either. I already have amplification in my antenna system, so that might have something to do with it.

Not surprising. Stacking amps is no bueno.

The orange sticks provide a better signal to noise ratio, which has a significant effect on decoding of digital signals.

These screen grabs were made using the same signal, same antenna, same time period. Let's see if they're legible...

 

[Ubbe]

I got two rtl-sdr and both have so small frequency errors that it can barely be compensated for. The SDR# software allows 1ppm as the smallest step but I need 0,6 or 0,7ppm. And 1ppm are 100Hz at 100MHz. I've tested how much error are accepted when demodulating a digital tetra signal and that was 3-4ppm before any degradation could be noted.

The important thing are not how much off frequency they are, that there are always ways to adjust for in the software, but how stable they are. Choose a stick that has a temperature compensated oscillator, tcxo, so it wont drift when it gets warmer from use.

All SDR USB sticks I know of have I/Q demodulators that are needed to properly decode simulcast signals. Uniden put a radio/tv/sat SDR chip in their SDS scanners to get that I/Q feature. Simulcast affects all signals, both control channels and voice channels.

/Ubbe

 

[maus92]

I got two rtl-sdr and both have so small frequency errors that it can barely be compensated for. The SDR# software allows 1ppm as the smallest step but I need 0,6 or 0,7ppm. And 1ppm are 100Hz at 100MHz. I've tested how much error are accepted when demodulating a digital tetra signal and that was 3-4ppm before any degradation could be noted.

The important thing are not how much off frequency they are, that there are always ways to adjust for in the software, but how stable they are. Choose a stick that has a temperature compensated oscillator, tcxo, so it wont drift when it gets warmer from use.

All SDR USB sticks I know of have I/Q demodulators that are needed to properly decode simulcast signals. Uniden put a radio/tv/sat SDR chip in their SDS scanners to get that I/Q feature. Simulcast affects all signals, both control channels and voice channels.

/Ubbe

The simulcast / multicast does affect all signals, but I can decode cch's from a farther distance than I can decode voice.

 

[jonwienke]

That's by design. Going the other way around wouldn't make sense--you can't use the voice channels if the control channel is unreadable.

 

[Volfirefighter]

I ordered the NooElec. Thanks for all the input. I am interested to see how this works.

 

[Volfirefighter]

I ordered the NooElec. Thanks for all the input. I am interested to see how this works.

 

[Volfirefighter]

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