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dk8cb
04-02-2006, 18:39
Hi,

recently, I notice a growing number of DRM tests on the 11m broadcast band.

Currently, we are in a minimum of the 11 year sunspot cycle and long-distance propagation is virtually non-existent on these frequencies. I very much doubt the significance of results obtained under these conditions and I'm afraid that results obtained now will be used in deciding whether to use this band for local DRM broadcasting or not.

What will happen when sunspot numbers are high again and such frequencies are used all over for local broadcasting?

I still remember the day, many years ago during a sunspot maximum, when I once sat in the lab and had a test receiver on, because we were testing a circuit, the kind of which I have since forgotten. A short piece of wire, perhaps half a metre long, was connected to the input of the test receiver, when I noticed a really strong carrier somewhere around 26 MHz. At first, we were convinced that because of the strength of the signal, the source of this signal would be inside the circuit we were testing or at least somewhere else in the lab. However, the carrier stayed on after we had removed the power to our circuit. Suddenly, there was AM modulation on the signal and it turned out to be Radio RSA, the Voice of Southafrica transmitting on this frequency. Of course, they were certainly using a highly directional antenna and a considerable power but the signal was also really strong, i.e. a in the tens of millivolts!

Now imagine propagation conditions like these and DRM stations all over broadcasting local programmes. What a chaos will result!

I'm writing this because it is my impression that in the evolution of DRM, other wrong decisions have already been made due to inadequate testing and because I want to prevent decision-makers from drawing false conclusions from tests that have been performed under idealised conditions. Currently available DRM modes also have not been tested thoroughly enough before putting DRM into regular service. Take e.g. mode B on 3995 kHz during nighttime hours which just doesn't work, even at ridiculously low bitrate. Also, other modes available do not provide any rescue since the quality that can be obtained is even worse. This is just an example, I could name more such examples and in my view, they are all a result of inadequate testing under real world conditions.

So don't draw any premature conclusions if it works now. Also think about whether it will work then.

Roland

df9rb
05-02-2006, 10:27
Hi,

I agree unconditionally with Roland!
I started my hobby more than 30 years ago with CB radio.
During the the sporadic-E season it was impossible to talk to my friends living around the corner on CB-radio in AM and DRM is more sensitive to interference. Professor Lauterbach who is responsible for Campus Radio on 26000 and 26012 kHz was running a longtime test. In his evaluation report (in German, 11 MB) he mentions clearly the problems caused by sporadic-E and also F-layer propagation which made reception in 8 km distance impossible. Thomas Lauterbach additionally mentions three other problems. These are occassional carriers, (I for example have 3 data carriers 24 h a day around 26 MHz!(attachment)), man-made noise and multipath reception inside the city fading out the DRM-signal.

Bernd, DF9RB

dk8cb
05-02-2006, 13:52
Originally posted by df9rb
Professor Lauterbach who is responsible for Campus Radio on 26000 and 26012 kHz was running a longtime test. In his evaluation report (in German, 11 MB) he mentions clearly the problems caused by sporadic-E and also F-layer propagation which made reception in 8 km distance impossible.

For those interested, a report by Prof. Lauterbach (in english, 1.8 MB pdf-file), which addresses these questions, can be found here (http://www.fh-nuernberg.de/fileadmin/Pressestelle/pdf/Lauterbach_Nr_31_fertig.pdf). Worth reading!

Roland

tacitus-ms
05-02-2006, 13:54
Originally posted by df9rb
Hi,

Professor Lauterbach who is responsible for Campus Radio on 26000 and 26012 kHz was running a longtime test. In his evaluation report (in German, 11 MB) he mentions clearly the problems caused by sporadic-E and also F-layer propagation which made reception in 8 km distance impossible. Thomas Lauterbach additionally mentions three other problems.Bernd, DF9RB

For everyone who is looking for this document, you can find it here:
http://www.ai.fh-nuernberg.de/Professors/Lauterbach/CampusRadio/DRM-Lokalradio%20im%2026%20MHz-Bereich.pdf


regards tacitus-ms

CT4RK
06-02-2006, 14:33
Hi all

Of course all the 26 MHz operators will go to have problems when the propagation goes up. As all know, only a few watts are necessary on this QRG to go to the F layer and get reflected up to thousands of kilometres away. With 200 or 300 watts with a SSN over 100 or so, is possible a world wide coverage on this QRG. In the propagation peak, the SSN would be more than 200, and the interference on the 26 MHz band in DRM would be terrible. I think the better band for local work in actual spectrum availability is MW, but maybe in the near future, when TV leaves the VHF low band, around 60 MHz (CH 2,3,4), this QRG would be optimal for local DRM coverage, also with power of under 50 watts.

tacitus-ms
06-02-2006, 18:21
Now where DVB-T is introduced the former VHF 1-TV Band will not be used any more. In these regions where the transmitters have already been shut down, VHF 1 (47 - 68 MHz) would be a good solution for a DRM test. Of course, it is higher than 30 MHz, and until now DRM is limited to 30 MHz, but this is only a political problem. Sorry, "only" is incorrect, in these days political, not technical arguments are used for such decisions.

regards tacitus-ms

DRM-OM
15-04-2006, 16:05
VHF 1 (47 - 68 MHz) would be a good solution for a DRM test. Of course, it is higher than 30 MHz, and until now DRM is limited to 30 MHz, but this is only a political problem

see this link (http://beradio.com/currents/radio_currents_030705/index.html).

DRM Votes to Extend its System to 120MHz
Paris - Mar 10, 2005 - The members of the Digital Radio Mondiale consortium voted to begin the process of extending the DRM on-air system into the broadcasting bands up to 120MHz. This decision will enhance the range of non-proprietary, digital radio solutions offered worldwide by the DRM consortium and the World DAB Forum, which work together on projects of mutual interest. In combination with one another, the digital systems of the World DAB Forum and DRM will provide digital systems, sometimes in the same bands, in markets across the globe.

DRM, a non-proprietary system that has been endorsed by the ITU, IEC and ETSI, currently covers the broadcasting bands below 30MHz (short-wave, medium-wave/AM and long-wave). DAB Digital Radio is also a non-proprietary system endorsed by the ITU and ETSI, which was developed to work in the broadcast bands between 30MHz and 3GHz and will therefore work satisfactorily in Band II (87.5MHz to 108MHz).

The World DAB Forum and DRM announced their cooperation at the IFA consumer electronics show in Berlin in 2003. DRM and the World DAB Forum hold regularly scheduled, joint meetings on key technical and commercial topics.

DRM will begin work on its band extension project right away. The design, development and testing phases are expected to be completed between 2008 and 2010.