[IRCA] DRM - how well it works

[Lee Reynolds <kd1sq@xxxxxxxxxxx>]

I've been listening to DRM for three or four years now.

Never heard IBOC - I refuse to pay $199 for something (the receiver) that should
cost $25 at most.

Observations on DRM and how it compares to people's comments on IBOC.

DRM sounds fine - better than AM SW, near FM quality - when it can be received.

Both encoding/modulation schemes have the same three problems -

- A drastically reduced coverage area.

- Extreme vulnerability to interference or propagation changes.

- Interference to adjacent channels.

DRM is more user friendly inasmuch as it's an open system and it's easy to see
what audio bw is being transmitted, what CoDec is in use, etc., etc. AFAIK
there are, at this time, no easy to use tools for divining what's going on in
an IBOC stream.

RCI regularly make DRM transmissions on behalf of various customers from
Sackville, Canada. I *may* be too close to Sackville for proper SW propagation
but I find that reception is spotty and frequency/time dependent. There is no
such thing as 24 hour reception of DRM. It's also heavily dependent on
bandwidth/FEC tradeoffs - the lower the audio bandwidth the more forward error
correction data that can be sent to render the signal more robust. One of the
more sublime examples of audio bandwidth versus error correction is being able
to receive a transmission from the middle east that's a S7-8 with a 11kHz audio
bandwidth (when decoded) whilst being unable to receive an S9+5 signal from
Canada that has a 22kHz audio bandwidth encoded in it.

There are tranmsissions from outside the USA but not a large number of them are
decodable on a regular or continuous (as in: no audio dropouts) basis.

BTW, for continuous audio decode without dropout you usually need a S9+15
signal. DRM, like IBOC, is in no way whatsoever a DX mode.

So far, apart from a few tests, I have yet to see any DRM station (decodable in
NA) making use of the data transmission facility that exists within it.

What it all comes down to, really, for both schemes is improved fidelity, vastly
reduced coverage, interference to adjoining channels (on AM and SW.)

Lee
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