What are the Actual step sizes and Bandwidths of a DMR UHF business band radio signal? 464.725, example, I am using a AirSpy SDR and have used 6.25, 12.5, and it barely comes over the screen. My Whistler scanner picks it up crystal clear. Are the signals in digital mode, Step size, Bandwidth the same as in Analog signals? If not reeducate me and that will be appreciated. Thanks.
DMR Bandwidths
- Thread starter Hearken
- Start date
Should be 12.5, I usually use a bandwidth of 7.6 (8 works too) for DMR. What are you using for an antenna on the SDR? How is your noise floor relative to the received signal? Make sure your gain is not set too high as to overdrive the signal or too low that it doesn't come in at all. What app are you using to drive the SDR & what app to decode?
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What software are you using? If Sdr#, pretty sure when you load that up for the first time, that the gain is on zero. If your Whistler is picking up crystal clear, and not the Airspy, look at gain, antenna and settings.
G7RUX
Active Member
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- Jul 14, 2021
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It is indeed 12.5 kHz but the two slots are TDMA, not FDmA; it uses half of the Tx time for each slot, still in a 12.5 kHz channel. There are some variants which have a physical channel of 25 kHz but these are not compliant with the main spec.
Frequency steps can be 6.25, 12.5 and 25 kHz.
Ubbe
Member
If you have a spectrum display you set the bandwidth so it just covers the signal. That goes for any modulated signal you have. It should be 12,5KHz for DMR and steps can be anything. But I have several cruising ships that only have a 6,25KHz wide modulation and then have problem to decode in a scanner that only do 12,5KHz in narrow mode and I have to use DSDplus or other programs with adjustable bandwidth to be able to decode it.
/Ubbe
What version of SDR# are you using? I have read posts that some of the newer versions have trouble decoding digital voice like DRM. This has been my experience as well, so I fired up an older machine with an older SDR# version and it was decoding again.
Ubbe
Member
I use an older version 1642 but I don't use a plugin, I use DSDplus via a virtual audio cable, or I use the IF out from TRX-2 that has better sensitivity than a SDR dongle and go directly to DSDPlus.
/Ubbe
/Ubbe
I had a similar problem, and after some experimenting I found that the SDR dongle sample rate will affect the ability to decode digital modes. Analog modes are more forgiving, but the digital modes require you're getting a good spectrum within the bandwidth you're trying to decode. Try slower sampling rates in your dongle settings. For me, 2.048 MSPS is the fastest rate I can use to cleanly decode DMR with Simple DMR.
