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Author Topic: DRM pirates  (Read 337 times)

Offline OgreVorbis

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DRM pirates
« on: July 23, 2020, 0244 UTC »
I've been looking into DRM recently and I found these products which seem more like something a pirate might use:
http://www.nti-online.de/edrg30.htm
http://www.nti-online.de/edrg30usb.htm

I am a bit confused about the process though. It seems to me like this may actually just be an SSB transmitter cause it looks like the PC is the source of the actual DRM signal. Is that how most DRM systems work, or do the professional transmitters generate the DRM inside them?
Are most DRM signals actually an SSB signal rather than AM? Could you generate the DRM on a PC and just feed that into an old fashioned AM transmitter? Yes, it would be less efficient, but does it work?

I am trying to decide what I'm going to do with my next shortwave transmitter. Do you think a super wide 15 kHz analog SSB signal made with an SDR would be better than DRM?
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Offline Stretchyman

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Re: DRM pirates
« Reply #1 on: July 23, 2020, 0551 UTC »
I see the prices aren't quoted...?

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Offline Brian

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Re: DRM pirates
« Reply #2 on: July 24, 2020, 1542 UTC »
I used the DReaM software to generate DRM about 16 or 17 years ago. I had to modify my high level audio MW transmitter in some way to take the coded signal. Can't recall exactly what I had to do but there were 2 outputs from the PC. One output went into the normal audio input on the TX and the other went to a small circuit that I had to put in the output of the PLL oscillator.
I don't think the mod is needed on modern transmitters though.

It worked.............sort of.  Not having a portable DRM radio was not ideal for field tests but I was able to decode it on another PC in the house with a modified radio.

Offline redhat

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Re: DRM pirates
« Reply #3 on: July 24, 2020, 2043 UTC »
Most professional DRM exciters, like AM stereo, produce a phase modulated carrier signal and a envelope signal to feed the transmitter.  To produce a compliant signal of sufficient quality to decode, a lot of alignment has to be done in the exciter to compensate for the response and group delay in the transmitter.  I did one trial about 8 years ago.  The signal output by dream can be either I/Q or just the composite waveform.  In my case, the IF input on my upconverter was used to modulate the DRM signal as double sideband.  By the time it fought its way through the amplifier chain I had about 50-75W of DRM power and it was heard by one guy.  It does work, I'm just not convinced of the utility of it with the power levels that most of us play with.

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Offline RobRich

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Re: DRM pirates
« Reply #4 on: July 26, 2020, 1938 UTC »
On a related tangent, FreeDV might be of interest for spoken-word and similar low-complexity content.
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Offline chanito

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Re: DRM pirates
« Reply #5 on: August 01, 2020, 2028 UTC »
The Spark product has evolved nicely. Trial version is here https://drm-sender.de/  Played with it back in 2006 for grins using a Ramsey FM transmitter, Spark audio output to the Ramsey analog in, decoded with FM portable and laptop running DReaM. Realize that's not really 'how it works' for DRM on FM, but it did work. Same with using DReaM aas transmitter. Might be fun to try the Spark AM+AMSS functionality on HF.
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Offline OgreVorbis

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Re: DRM pirates
« Reply #6 on: August 04, 2020, 1421 UTC »
I used the DReaM software to generate DRM about 16 or 17 years ago. I had to modify my high level audio MW transmitter in some way to take the coded signal. Can't recall exactly what I had to do but there were 2 outputs from the PC. One output went into the normal audio input on the TX and the other went to a small circuit that I had to put in the output of the PLL oscillator.
I don't think the mod is needed on modern transmitters though.

It worked.............sort of.  Not having a portable DRM radio was not ideal for field tests but I was able to decode it on another PC in the house with a modified radio.

Huh, didn't realize this was that old, surprising.
I see, so it's the same way as c-quam. Maybe I'll test it someday...
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