Digital Part 15 is Coming

Thanks for the link. If digital radio works as does digital TV then this wouldn't bode well for part 15 in that the signal is either received or it isn't with no in between. Since part 15 AM signals are so weak it would appear that reception would not work unless under ideal conditions. Nonetheless, the field is wide open for experimentation and development.

Perhaps the all or none characteristic need not be in play since there are other ways to deal with weak signals. Error detection and correction can be used as well as modifying the bandwidth to provide reception with a weak signal.

Shannon's Rule says C = B*ln(1 + S/N) which means that for a theoretical digital channel the capacity is proportional to the bandwidth times the natural log of 1 plus the signal to noise ratio. With a weak signal the signal to noise ratio is lowered and the channel capacity (received bandwidth) is reduced. This tells us that one response to a weak signal is to narrow the bandwidth rather than just blanking the signal. This is one approach which can be investigated.

It's the old chicken and egg scene where either the transmission system or the receivers have to come first, but as David Sarnoff realized and proved one can implement the transmitters and the receivers will follow providing there is content listeners want to hear.

Neil

I read a very rare seldom noticed bible passage that says:

"In one gesture both chicken and egg were created equal, and the chicken thought, "Oh, good. Eggs for breakfast!""

I have heard a few things about DRM.

Some SWBC stations have used in

in Europe, I think.  I know that the BBC

transmits a DRM signal on 3955 kHz.  When

that broadcast was AM, I would hear them

no problem in the winter time - BUT with

DRM, who knows?  I do know that DRM isn't

like IBOC in the sense that there is no analog

voice transmission available for the radio to receive. 

It's just a straight digital emission. 

I heard about one ham who - well I think it's

true - this guy made a DRM receiver with

one 12BE6 (???) tube and fed the 12 kHz

output to his computer.  It worked.  (?)

Yup, I guess the thing is 12 kHz wide.

So, you have to get that from somewhere -

either from inside an existing radio, or

another way.  I know of one SW radio

available in the U.S. that has a 12 kHz

DRM out, which would be fed to a

computer. 

There are receivers available in Europe that

tune in the mode. 

That's all she wrote, Jack.

Bruce, DOGRADIO

PLAN A -- During the FCC shutdown is a good time to start this project.

Download the DRM software linked by John Anderson.

Have a 60-foot insulated HAM tower set up in the yard.

Feed the tower with a 10-Watt transmitter from R.I.S.

Transmit DRM.

Your transmissions might only last a few weeks but maybe you'll be on for years.

IF a NOUO arrives in the mail or an inspector visits, cite the following Rule"

15.7 (b) No authorization is required to perform testing of equipment...., but agree to comply and leave the air at once.

Resort to PLAN B, 15.7 "Special Temporary Authority," (a) in exceptional situations the Commission will consider an individual application for special temporary authorization to operate an intentional radiator... where it can be shown that the proposed operation would be in the public interest.

In fact. why aren't we talking more about 15.7 for Part 15 public service stations?

There's work to be done. We can't wait until the government gets its act together.

Plan A clearly advocates an unlicensed system guaranteed to be non-compliant with FCC §15.219.  The proponent of such appears to be relying on its operator not being detected by the FCC during their current shutdown.

Plan B cannot be justified, because an unlicensed station would not be granted temporary authority to use DRM by the FCC to operate "in the public interest," if almost no DRM receivers are present in the coverage area of that station to receive/demodulate such signals.

Plan A is based on the argument that experimentation is allowed, but anticipates that the FCC might rule other wise, in which case a shutdown would be appropriate.

I agree fully with Rich on Plan B based on the public being unequipped for receiving DRM. There does not seem to be a public service claim in this case.

But all this has raised a much larger point that the pushers of digital radio want us to ignore.... mainly, that digital radio is inefficient and in no way an advancement over traditional analog radio.

Down with digital radio.

...But all this has raised a much larger point that the pushers of digital radio want us to ignore.... mainly, that digital radio is inefficient and in no way an advancement over traditional analog radio. ...

Suggest that the "radio" part of this audio path is not the biggest limitation to the sonic quality of the programs they convey.

The ultimate audio quality possible from a digital process such as provided by the compact disc and other means is far superior to the ultimate audio quality of most analog processes -- especially after having been transmitted via analog AM/FM/FM Stereo, and received by a typical, analog, consumer-level radio receiver.

Above I said I "agreed fully" with Rich on Plan B. Not so much any more.

I believe the argument could be mounted, in the effort to justify receiving "temporary authority," that a radio station was "exploring" public service uses of DRM radio in the low power class. It might help the argument along to have a few speculative examples of how this might happen, but that speculation could be placed in suspension until the authority is granted.

Limiting one's own imagination seems very tea party.

I just read a few more things about DRM.

It is actually very interesting.  Some countries

(Such as India, I think) are rolling it right out

right now.  There are countries in that part of

the world that still have a lot of medium wave

transmitters, and listeners for those transmitters.

I think the idea would crash and burn here.

One very interesting thing: I read that DRM goes

as far or farther than anolog during the day.  BUT

as we can expect, as night, DRM on the AM BCB

is a disaster.  However, I think some of these

countries that are trying it are switching frequency

allocations around, so that DRM signals on the

AM BCB get little or no interference at night. 

Anywayyyyyyyyyy...

A couple of years ago during the BIG STORM

where almost a million people in CT didn't

have AC power (yup I know I seem to mention

this almost every day) my crystal radio receiver got the

local flame thrower without any problem.  WTIC

AM 1080, 50,000 watts is only 3 miles from my

house.  I am actually rigging my crystal set to

drive a small speaker (without any power source.)

  Quite a few people have

done this successfully.  DRM sure won't help you there.

For those who don't know, a "crystal set" is a radio that

operates just on the power of the radio signal in the air. 

These were used in the beginning of radio 100 years ago.

In the last few decades, a lot of electronics enthusiasts

have started making crystal sets just for fun.  There are

tons of web pages on the subject.  Very cool.  But no

good for DRM.

Bruce, DOGRADIO

Mr. Rich claims:

"The ultimate audio quality possible from a digital process such as provided by the compact disc and other means is far superior to the ultimate audio quality of most analog processes -- especially after having been transmitted via analog AM/FM/FM Stereo, and received by a typical, analog, consumer-level radio receiver."

While Rich is right, as always, his timing is amiss.

The time for excellent audio quality passed us by. That was generally the 50s, 60s and 70s when quality music was still around.

But since then the public has accepted toy music played on hobby toy guitars with male vocalists shouting and female vocalists howling. How much audio quality do you need for that?

Are you claiming that we need an undistorted medium to reproduce the distortion that modern music amounts to?

I say that Part 15 radio should be the clinger on to analog transmission as the only, in the final analysis, authentic kind of radio.

The only restriction on modulation for part 15 AM is the prohibition of damped waves. Otherwise there should be no problem with experimental modes providing one stays in band and doesn't cause interference.

Neil

I'm not optimistic about digital Part 15 other than for hobby experimentation.

HD Radio aka IBOC is pretty much out of the question. Ibiquity requires a license royalty for the privilege of using their system!

DAB and DRM are open source, so royalties aren't required. At least that's sensible!

Aspisys had a part 15 DRM transmitter on the market for a few years and then stopped selling it a few years ago. Info doesn't seem to be available to determine if it didn't work properly or there were just insufficient sales. Google is pretty much silent on this thing.

Free or low cost DRM encoding software is available for download on the web. It produces the requisite CODFM (coded orthogonal frequency division multiplexing) output from the sound card in the "base band" frequency range of roughly 0 to 20 kHz range. Trouble is, you can't just plug that in to the audio input of a part 15 AM or FM transmitter. It must be up converted to the final transmitting frequency to preserve all the QAM sub channels. The simplistic view of "up converting" is to do a heterodyne mix with a local oscillator, but actual implementation is not simple due to the need for precise filtering so as not to wreck the amplitude and phase relation of all the subcarriers. This is a job best performed by DSP (digital signal processing). This is heavy engineering work that is immediately out of the question for an affordable transmitter in the small part 15 niche market.

There are DRM receivers on the market, but the market is unstable. About half of the receivers have been discontinued and the rest are going for fire sale prices. DRM is not catching on despite the sporadic announcements that some shortwave broadcaster is starting experimental DRM broadcasts. Others have discontinued their experiments. Heck, most of the shortwave broadcasters are just plain shutting down.

All the various systems are market driven. Everyone is searching for the new holy grail. All the systems are actually fragmenting the market and eventually seem to be doomed to failure. Good old analog AM and FM are still the best bet for part 15, at least until they too are completely fragmented out of existence.

I will tell you why PhilB is right.

Part 15 AM radio should remain the mainstay of analog radio on AM medium wave.

If licensed stations decide to go down in a digital fire storm, we should hold fast to the analog tradition.

Why?

Because digital will fail and disappear, but the tens of thousands of AM analog radios will continue to exist and Part 15 radio stations will be their only hope of daily programming.

The solution to the future is to push and promote AM Part 15 radio.

Carl asked: "In fact, why aren't we talking more about 15.7 for Part 15 public service stations?"

I think the difficulty lies in convincing the authorities that the "proposed operation would be in the public interest", and what the "exceptional situation" is.  What kind of documentation is needed? What kinds of records or proof of community involvement would support one's case?

I'm all for the idea Carl, especially since lots of 15'ers run microstations that super-serve their neighborhoods. I just think the guy spraying his community with his vanity bluegrass collection is going to have a rough time convincing the authorities that he's doing something that qualifies.