SDRTrunk sdrtrunk decoding question

[sierratango76]

Hi
I'm new to sdr, i got my first nooelec dongle just yesterday. I would be interested in listening to digital communications (drm, p25 and tetra), I have seen that many people use sdrtrunk software for this. I watched videos on youtube on the use of this software and saw that the frequencies are downloaded from the radioreference database. The problem is that there are no frequencies listed in the country where I live. Despite this, I know some digital frequencies in my area, but without knowing the type of transmission used (drm, p25 or tetra). How should I proceed to listen these broadcasts? do I have to enter the frequency manually in the sdrtrunk database and select a decoding mode until the transmission becomes clear? logically always that there is no encryption key in the signal. I hope someone can answer me and give me also some advices for to listen digital communications. Thanks and greetings. SierraTango

 

[krokus]

Start with listening to your local FM broadcast radio stations, to get a grasp on how to control the SDR. Then start expanding into any local FM two-way radios, so you know things are working. Then work on decoding the digital signals.

If you are willing to share which country you are in, others may be able to help.

 

[maus92]

Hi
I'm new to sdr, i got my first nooelec dongle just yesterday. I would be interested in listening to digital communications (drm, p25 and tetra), I have seen that many people use sdrtrunk software for this. I watched videos on youtube on the use of this software and saw that the frequencies are downloaded from the radioreference database. The problem is that there are no frequencies listed in the country where I live. Despite this, I know some digital frequencies in my area, but without knowing the type of transmission used (drm, p25 or tetra). How should I proceed to listen these broadcasts? do I have to enter the frequency manually in the sdrtrunk database and select a decoding mode until the transmission becomes clear? logically always that there is no encryption key in the signal. I hope someone can answer me and give me also some advices for to listen digital communications. Thanks and greetings. SierraTango

There is spectrum analyzing software that will allow you to examine frequencies in a waterfall display - like SDR#. Digital modulations present certain patterns that you can use to identify what "flavor" of modulation is being used on a particular frequency, and sometimes by listening to the audio.

Signal Identification Wiki

This wiki is intended to help identify radio signals through example sounds and waterfall images. Most signals are received and recorded using a software defined radio such as the RTL-SDR, Airspy, SDRPlay, HackRF, BladeRF, Funcube Dongle, USRP and other devices.

www.sigidwiki.com

 

[sierratango76]

I've tried some digital software decoding but the best results is with sdrtrunk. I've another question about the signal..I manually entered a series of frequencies where the transmissions are in dmr and some of these are decoded correctly, while others only hear the initial call and then no longer hear anything, that is, it feels like an "empty" call (on sdrtrunk appear also the "call" in blue color). If I have not misunderstood, I am unable to listen this broadcasts not because it is encrypted, but because the signal level is low. Is this possible? what advices can you give me? for info, I live in a condominium and I have a discone antenna on the roof with about 35m of direct cable down to the scanner. The cable is not an rg58, I don't remember exactly the type but it is thicker and better than the 58.

 

[Shin]

I'm pretty much in the same situation as there is no database also for my country Switzerland. The link you got to the SigInt wiki can help to identify signals.
If you loose a call in SDRTtrunk, you probably don't have the right LSN's configured in the channel setup. I'm trying to do this right now, too. Look in details if it says 'Channel grant – NO FREQUENCY …', then it's missing Frequency/LSN.
Yes, you need a strong signal for a good decoding. SNR >14db would be good. Else you got dropouts in decoding and bad voice quality.

 

[sierratango76]

I'm pretty much in the same situation as there is no database also for my country Switzerland. The link you got to the SigInt wiki can help to identify signals.
If you loose a call in SDRTtrunk, you probably don't have the right LSN's configured in the channel setup. I'm trying to do this right now, too. Look in details if it says 'Channel grant – NO FREQUENCY …', then it's missing Frequency/LSN.
Yes, you need a strong signal for a good decoding. SNR >14db would be good. Else you got dropouts in decoding and bad voice quality.

Thank you Shin for your info, can you explain me better how to set the LSN frequency?

 

[krokus]

I've tried some digital software decoding but the best results is with sdrtrunk. I've another question about the signal..I manually entered a series of frequencies where the transmissions are in dmr and some of these are decoded correctly, while others only hear the initial call and then no longer hear anything, that is, it feels like an "empty" call (on sdrtrunk appear also the "call" in blue color). If I have not misunderstood, I am unable to listen this broadcasts not because it is encrypted, but because the signal level is low. Is this possible? what advices can you give me?

DMR can send data, could those be data transmissions, not voice?