Re: [Drm-devel] MDI based transmissions, Experimental live broadcast in Budapest

[Ádám K. <kis...@si...>]

Hello!

DReaM doesn't generate baseband IQ signals since our soundcard cannot
output low frequenty signals, and also the (presumably) different
phase-shit difference would kill the signal quality after the generator. We
are using a 12 kHz intermediate frequenty.
The IF is 12 kHz, and we are putting positive IQ signals to the vector
modulator. (The left is the I and the right is the Q channel) The SMIQ is
just a temporary solution, we will change it to my homemade IQ modulator
built from two SA612, and a passive, fix-freuqnty phase-shifter. This
already works, but we are going to reduce its EVM under 5% before we
install it permanatly.

We are using our homemade pre- and power amplifier. Nowdays I am not at the
university, so I cannot take any photo.

We are using a monopole antenna tuned to the desired freq (26060 kHz) with
a network analyzer.


With further investigation in the code I found that implementing the MDI
transmission would require some other changes. For eg. implementing
hierarhical modulation with service priority and run-time change between
modulation types. it's a bit different to implement them without previous
experance with the project.

Bests, Adam

Stefano Mollo <ste...@gm...> ezt írta (időpont: 2019. jún. 10.,
H, 17:36):

> Hi Adam,
>
> excellent initiative and I can confirm that the MDI feature in TX mode is
> not yet implemented; I wanted to do exactly the same you are trying to do,
> and I learned it "the hard way", after few days of banging my head against
> the .... PC monitor :-) !!
>
> However I am VERY much interested in some more detailed description of
> your TX setup; such as:
>
> 1) you write that DREAM generates the baseband IQ samples of the DRM
> signal to be transmitted, then outputs these IQ signals through a
> SoundBlaster Live! card, which you feed into a Rhode & Schwarz IQ modulator
> (R&S SMIQ).
> *Question*: what settings - and why - exactly do you use in DREAM TX in
> the "OUTPUT" dialog box? (The default is shown below)
> [image: image.png]
>
> For example, if you set it to
> [image: image.png]
> then how do you know which channel is* I *and which channel is *Q*? I.e.,*
> I* will be on the Left or on the Right channel of the sound card output
> port?
>
>
> 2) you continue writing that the  Rhode & Schwarz IQ modulator then drives
> the consecutive power amplifier chain and antenna;
> *Questions*:
> (a) what power amplifier are you using? Characteristics, brand, model ....
> etcétera;
> (b) are you using any filtering between the amp and the antenna?
> (c) what kind of antenna are you using?
> (d) are you using an antenna tuner? If so, could yo please describe in
> details what are you using?
>
> ===
>
> See, I have been trying to do exactly what you are doing for about a year
> now, but I am stuck at the DREAM output stage, and I never managed to go on
> air. I did, however, managed to send the DREAM I/Q stream over IP, and it
> worked VERY well, with SNR > than 60 dB at the receiving end! REALLY really
> good stereo quality,using OPUS ;-)
>
> Finally, the R&S modulator is probably something a normal person can
> afford; any idea for a simple I/Q modulator, say, re-purposing some
> Electronics originally meant for other uses? For example, how about using
> the PI as a modulator taking advantage of the RPI TX project?
>
> Cheers, and congratulations for the initiative; I firmly believe DRM is
> THE way to the future for radio.
>
> Stefano Mollo
> Perth, Western Australia
> VK6WFM
>
> On Sun, Jun 9, 2019 at 11:35 PM Ádám Kiss <kis...@si...>
> wrote:
>
>> Dear DReaM Developers,
>>
>> I am a student of the Budapest University of Technology and Economics,
>> taking part in our DRM transmitter project. Basically we are on the air
>> now, aiming to provide opportunity for signal propagation experiments and
>> receiver tests still in the development phase.
>>
>> We currently play out a 25-hour prerecorded program via mplayer to the
>> onborad soundcard of a PC running Linux. Dream receives the data of the
>> monitor port of this card, encodes the sound using FAAC, generates the
>> baseband IQ samples of the DRM signal to be transmitted, then outputs these
>> IQ signals through a SoundBlaster Live! card, which we feed into a Rohde &
>> Schwarz IQ modulator (R&S SMIQ). This later one drives the consecutive
>> power amplifier chain and antenna. (Further details can be found on
>> www.drm.org and the monitored transmission is available here: nmhh.hu/drm
>> ).
>>
>> Since our goal is to provide opportunity for all receiver manufacturers
>> worldwide to test their products on a live system, we intend to transmit a
>> stream which contains Journaline data and slide show as well in addition to
>> the audio data. To this end we would have to feed an MDI stream into the
>> DREAM modulator software. We tried to reconfigure DReaM to use this data
>> stream, then we saw that this feature is not implemented yet. I checked the
>> source code of DREAM and saw that MDI decoding is implemented, although it
>> is not integrated with the transmitter module.
>> Do you have any plans for implementing this feature in the near future? I
>> would like to rely on free software as long as I can, and DReaM fits well
>> to this objective.
>>
>> Thank you for your consideration.
>> With best regards
>> Adam Kiss
>> Budapest University of Technology and Economics
>> Department of Broadband Infocommunications and Electromagnetic Theory
>> HAM: HA8KDA
>> _______________________________________________
>> Drm-devel mailing list
>> Drm...@li...
>> https://lists.sourceforge.net/lists/listinfo/drm-devel
>>
>
>
> --
> *************************
> Stefano Mollo
> MARA <http://www.mara.gov.au/> Registered Migration Agent
> MARN 1570954
> MIA <https://www.mia.org.au/> member No. 11033
> Level 2
> 524 Hay Street - Perth CBD 6000
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