Recording of "Clean" AM vs AM with HD

[Tom Wells]

I mentioned this recording in other threads, but felt this ought to have its own tag/topic.
http://fishingmeter.com

Please go to the "Contact Us" page, and click the audio file link at the bottom. You may have to wait a minute for the file to load,
and may have to unblock pop-ups.

This recording is intended to show the frequency capability of AM radio, and the self-interference created by HD sidebands on AM.

I recorded this on a 1983 GE reproduction cathedral AM/FM radio with a -60 db 10kc notch filter.
This radio has 2 IF stages and no ceramic or crystal filters, with AM response to over 15 khz.
All clips recorded from the AM, with no changes made to tone control during recordings.

Clip 1 WLUP AM 1000 analog only, full NRSC mask, as crisp as any AM is today.


Clip 2 WFMT FM 98.7 analog FM received on Sansui TU-7700, rebroadcast on home part 15 AM at 1550 khz.
Sounds like some SCA noise in the background.

Clip 3 45 rpm record chosen at random, also broadcast on pt 15 AM 1550 khz. Light reverb added.
Original recording distortion at 3-4 seconds into the clip is clearly audible.

Clip 4 WGN AM 720, WBBM AM 780, and WLS AM 890.
Once center tuning is achieved, listen to how muddy the remaining audio is.
Notice the apparent loudness of the sidebands while tuning compared to the analog.



Next, I will document the adjacent-channel noise.

 

[radiopilot]

Great recording Tom... I could listen to the difference between the two.. the first clip is very good and is similar to what I get here on 630AM and also on 1290AM during the day.. at night they give in to noise.. mostly HD interference especially on 1290AM...

The second clip is good too, the noise you mentioned is apparent... but otherwise good tonal quality.

The third clip, you can tell it's a 45 playing on a low power transmitter... by the way which Part15 transmitter are you using?

The last clip is similar to the recording done by the obvious unmentionables on these boards... mushy sounding and with no quality... sounds like my son's Fisher Price toy cassette recorder when he one.

You've proven again that these guys are blinded by the fact they 'earn' a living on these HD radio stations and have to sell their soul or be on the unemployment lines....

Radiopilot

 

[Tom Wells]

The same part 15 transmitter on 1550 is used for both the FM-originated audio and the 45 rpm audio.
The 45 has its own weird type of distortion, but this is what you're hearing.
I could have picked something pure, but this was a random pick to show transparency of distortion or whatever was original.

The design is my own, with a Colpitts oscillator using a 6L6 or 6V6 with voltage regulator,
Van der Bijl low-level modulator in the last of three 6SN7s for audio, mike, reverb, and tone controls, a 78 for a voltage amp (just because they're so beautiful with a top grid cap), and a really, really weak 100mw input 6L6 for the output into a leaky coax arrangement.
I've had one 'lytic capacitor failure since 1990, taking out a resistor and a transformer.
Only down for a few hours out of 16 years, I'm happy.
I did some cleaning a month or two ago and found a broken cap on the bottom of the modulator board, and now the tone controls are
"funny". Haven't replaced it yet, I just leave the tone controls set where they behave.
Why tubes? C'mon, that makes it more radio-ey.

I almost appended a recording of WMAQ as a news station in 1992. The audio is SO clear and sharp. Maybe later.

 

[4dude]

All AM stations running IBOC sound like crap in analog for 2 reasons

1) THEY DONT KNOW HOW TO PROPERLY PROCESS IT

2) IT EATS UP ALL OF THIER BANDWIDTH..

 

[Tom Wells]

I have tested the link from various computers, and the link seems to work.
Thank you for your kind comments, Radiopilot.
As I have heard no other direct comment, particularly from our professional broadcast regulars,
I assume all are in agreement that the present practice is vastly inferior to the technology's potential.

Also that the center-tuned AM result is like unto a heavy woolen blanket grille-cloth of 6 layers.

Suggesting we accept this sort of super-dull audio as our new lot in life is unacceptable.
Backward compatible was the promise when in fact, the result truly is backward-destructive.
A truly disruptive technology.. there has been some buzz about that in the recent past...guess ibiquity thought if they could
get the FCC to grant them an indulgence, they could foist a fine disruptive technology on the public to their benefit.

I would very much appreciate the comments of our radio professionals.
Have real reasons for dismissing my issues with the audio.
Intelligibility suffers in any high-ambient noise situation, especially at low volumes.
I still hear to 19 khz, so don't suggest my hearing is bad.

I really think we shouldn't try to make the AM "do digital".
It works fine in digital at CW rates, but the result at such a high data rate can only be incompatible.

The lower speeds generate the same wideband hash contributing to the general noise floor inasmuch as the shouder of the square wave is truly square.

Round off the corners, and you don't create the problem, but cannot achieve high speeds.
Ask any ham about someone who sends at 30wpm sloppy, but can only copy at 10.
Ask an "extra" about copying at really high speeds. Or a signal from a bad transmitter at high speeds.
Ask them about filters used to "round off" their CW so as not to create... "interference".

Higher speeds ensure as "square" a pulse as possible, exacerbating the incompatibility ibiquity enjoyed in the "spectral regrowth" issue.

Where were the RF enigineers in ibiquity?
Apparently none with enough RF experience to see the various problems with MW AM implementation.


Hasn't a one of them ever had to chase a "birdie" out of radio?
Or explain why the TV makes a funny noise on the radio to a family member?
Lamp dimmer noise, anything?

Some things should never be digital, like smell, taste and pressure.
But somone will surely find a way, for everything MUST become DIGITAL.

When we ever get around to digitizing the steering in a car, I hope I'm already dead.

If anyone has had a problem with the link or audio, I will move it to a file sharer.

 

[SUPERCASTER]

Thanks Tom for posting your audio files.
I have recorded several local AM and FM iBiquity/HD noise examples as well, but I'm sure they would be dismissed, criticized and ridiculed by the iBiquity/cartel's HD peddlers who remain stubbornly in deep denial (for political reasons)? They have posted their limited, contrived audio files, and claim universal absolute proofs of audio and RF perfection with no interference, in spite of the fact that what they posted does not prove anything, except their personally motivated bias and intransigence.
Perhaps I'll eventually post my airchecks for the many who are not already religiously committed to this very destructive and unnecessary iBiquity/cartel adjacent channel version of HD Radio.
The iBiquity/HD radio discussion seems to have a few faithfully committed fanatical supporters of iBiquity's version of digital HD ideology, opponents (mostly top RF engineers) who oppose it on technical grounds, and a vast majority who are either confused or could care less about iBiquity's version of HD Radio, and have no use for it.

 

[clouseau]

Thanks Tom for posting your audio files.
I have recorded several local AM and FM iBiquity/HD noise examples as well, but I'm sure they would be dismissed, criticized and ridiculed by the iBiquity/cartel's HD peddlers who remain stubbornly in deep denial (for political reasons)?

You know, you accuse people of making things up and then surprise us all by playing the
"I have plenty of recorded examples, but I won't post them because they'll make fun of me" card.

Grow Up!

They have posted their limited, contrived audio files, and claim universal absolute proofs of audio and RF perfection with no interference, in spite of the fact that what they posted does not prove anything, except their personally motivated bias and intransigence.

Your conclusion is a blatent falsehood. I know you're sitting there feeling sorry for yourself, asking all of us to cry with you because you're ridiculed. NO ONE that I recall has EVER said there is RF Perfection. If that makes you feel less hurt to say that then go ahead.

Perhaps I'll eventually post my airchecks for the many who are not already religiously committed to this very destructive and unnecessary iBiquity/cartel adjacent channel version of HD Radio.

Of course by then we won't have you little dog checkers to kick around anymore, either.

Sorry to be harsh, dude, but c'mon. Did the dog eat your homework? Did you accidentally drop the recording down the sewer?

You have tons of Iron Clad proof, but you won't show it to us.

Good Take,

Clouseau