View Single Post
  #4   Report Post  
Old May 11th 07, 06:12 PM posted to rec.radio.shortwave
Mark Zenier Mark Zenier is offline
external usenet poster
 
First recorded activity by RadioBanter: Jun 2006
Posts: 237
Default What a Pleasure Hearing HCJB Again

In article ,
Brian O wrote:
I wasnt aware of this. What is DRM exactly?


Digital Radio Mondiale (Worldwide Digital Radio, or something like that).

It's another method of sending a digital bitstream in a relativly
narrow bandwidth. It sends, using COFDM (a whole lot of closely spaced
subcarriers, phase modulated), a 9 or 10 kHz wide signal that can be
demodulated into a 30-40 kBPS bit stream that carries one or more lossy
compressed (MP3/ACC?/Ogg) audio signals. Unlike IBOC-AM a.k.a. HD-Radio,
it doesn't bother with an analog listenable signal.

It shows up as a 10 kHz wide block of rushing noise on AM, and on
SSB, you hear the various subcarriers zipping up and down. Very similar
to a multiplex radio telegraph signal, only about 4 times as wide.

Radio New Zealand often uses it on 15720, and Radio Canada on 9800.

The usual hobby way to receive it is to get a reciever that has
an IF output in the audio range (2-12 kHz?), feed that into a
computer's sound card, and throw a whole lot of CPU cycles at it.
There are standalone Digital Signal Processor chips that will
demodulate it (along with several other modulations, more commonly
used in Europe), so regular receivers are showing up this year.

My opinion of it is that it was developed by regional broadcasters in
Europe as a way to deal with getting shut out by the conversion to digital
by various national broadcast systems and satellite systems. One of
the more interesting uses is Radio New Zealand, who, (I gather), uses
it as a "poor man's satellite", to feed various FM band rebroadcasters
throughout the Pacific Ocean area.

Mark Zenier
Googleproofaddress(account:mzenier provider:eskimo domain:com)