[HN Gopher] Open Source DMR Modem Implementation in SDR with GNU...
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Open Source DMR Modem Implementation in SDR with GNU Radio and
Codec2
Author : threeme3
Score : 88 points
Date : 2025-04-19 12:23 UTC (10 hours ago)
(HTM) web link (qradiolink.org)
(TXT) w3m dump (qradiolink.org)
| lpribis wrote:
| I see this is only tier 2 for now (conventional channels) and not
| tier 3/trunked yet.
|
| Are trunked networks ever used in amateur radio or outside of big
| commercial/government systems? Is there a standardized way to
| feed back channel info to the SDR frontend for trunked operation
| in GNU Radio? Eg. The control channel will tell the terminal to
| tune to traffic channel at X Mhz to receive or send a call, which
| requires reconfiguring the frontend.
| birdiesanders wrote:
| Trunked is essentially useless to HAMs, and we never really use
| it much. We have essentially everything that trunking was meant
| to solve for a company; large pre-authorized spectrum space,
| self-coordination in that space without having to get fcc
| involved. Use of 25khz FM where part 90 is now only 12.5 also
| is enabled by being a ham.
| mschuster91 wrote:
| > Use of 25khz FM where part 90 is now only 12.5 also is
| enabled by being a ham.
|
| Y'all can use 25 kHz for repeaters? Here in Germany repeaters
| are 12.5 kHz only, allegedly due to a lack of free
| frequencies...
| colanderman wrote:
| In the US frequency allocation within each band (including
| repeaters) is left up to regional spectrum management
| organizations (which have no legal authority). So it varies
| by region.
|
| Here is the allocation for eastern New England for example:
| https://nesmc.org/docs/nesmc_bandplans_2023.pdf On the
| crowded 2m band we have 20 kHz for major repeaters and 9
| kHz for smaller ones.
| wolrah wrote:
| > Trunked is essentially useless to HAMs, and we never really
| use it much.
|
| I wouldn't say it's useless, but the utility is reduced
| because we typically don't have the density of users where
| two timeslots on a single channel becomes a real limiting
| factor. A repeater that's set up for local talkgroups on one
| timeslot and then open access on the second is generally more
| than enough unless you have a lot of people trying to use it
| at once, especially in a world where anyone who wants to can
| have their own personal hotspot for less than the cost of a
| HT.
|
| Also the usual "ham not HAM" thing.
| ac29 wrote:
| > part 90 is now only 12.5
|
| This is wrong. 25kHz part 90 licenses are still available so
| long as the system meets the minimum efficiency standard
| (19.2kbps or better for 25kHz).
| Calwestjobs wrote:
| many SDRs can RX/TX spectrum many times wider than you think is
| required in here.
|
| Try to look at this small enthusiast SDR receiver -
| http://g4wim.proxy.kiwisdr.com:8073/ /
| http://kiwisdr.com/public/ you can see that simple 350$ radio
| can have 100s of "channels" visible/receivable at once.
| (digital modes are available in bottom right "toolbar", in top
| right corner, drop menu called "extensions" )
|
| so with (different) SDRs you no longer need to choose one
| channel and listen to it, you can receive 200 channels at once,
| storing that data and choose what channel you want to decode
| later
|
| or decode multiple radio stations realtime at once, even each
| with different mode (AM/FM/Olivia/USB...) and you can even
| (UNIX) pipe data from it, to programs not designed for ham /
| sdr use. data is just data as soon as you have it you can do
| anything with it. you can even write program/script to send
| email/notification/sound when specified callsign makes
| call/connects to trunk. for billing purposes...
|
| or BTS/repeater can listen to 50Mhz wide part of spectrum
| 400Mhz-450Mhz AT ONCE realtime so no "tuning" necessary. for
| example 2000$ USRP can do that (but you need amps, filters etc
| to make full BTS )
| fsiefken wrote:
| I wonder if Codec2 could be replaced by one of the low bitrate
| neural audio codecs, HILcodec and SementiCodec sound better at
| 2-3 kbps.
|
| https://arxiv.org/pdf/2405.04752
|
| https://arxiv.org/pdf/2409.14085
| Calwestjobs wrote:
| i rather transfer few bits of text with text-to-speech and
| speech-to-text on end device, providing much better experience.
| and technically with 2kbps it is not very different than what
| these codecs do.
|
| depends on device, on one hand there are handheld radios which
| have small ARM for UI and control of dedicated radio chip, and
| then there are mobile phones/laptops/tablets with so much
| neural processing on board that it can have model sounding like
| person/celebrity of your choosing.
| glzone1 wrote:
| I really wish we could find some "HD" voice codec / mode - all
| the SIP protocols have gone pretty HD / zoom etc are HD at this
| point, a lot of cell has gone HD.
|
| Are the bands really so crowded (think on 70cm?) that we can't
| afford the bandwidth for something a bit more HD?
| tarxvf wrote:
| https://www.openresearch.institute/opv/
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