Digital noise at 758 kHz

[kenw2dtc]

When you tune just above and just below one of the new AM broadcast stations, you hear what I call "digital noise".  I'm hearing the same noise at 758 kHz and there is no station plus or minus 8 kHz from 758.  Is this something weird at my location or does someone else hear it too?

73,
Ken W2DTC

[Pete, WA2CWA]

Sounds and looks like it's coming from WABC 770 KHz

[kenw2dtc]

You could be right Pete.  It's 40 over 9 at 758 and 15 over at 753 before it drops off. 

Geez, when someone tells you that your signal is "broadcast quality", it brings that phrase to a new level.

Ken

[Pete, WA2CWA]

I can hear the "noise" clearly on the Sony HD AM/FM radio I have here in the office. It also audible on 780 KHz. On the Flex, the spectrum analyzer shows the signal above the base line from 752 to 788 KHz.

[W8IXY]

Hi everyone,

I am a broadcaster who works on audio processors and transmitters, and WA2CWA has it exactly right.  The digital carriers of AM HD extend about 18 kHz on both sides of the carrier.  So WABC's nominal occupied bandwidth runs from 752 kHz to 788 kHz.  Funny thing, back in the early 90's, the FCC adopted rules where the analog sidebands of AM broadcast stations must be sharply attenuated beyond 10 kHz from the carrier to reduce second adjacent channel splatter.  However, the digital sidebands now extend to about +/- 18 kHz from the carrier.  Talk about second adjacent channel interference.....  And the analog sidebands when using HD are restricted to no more than 6 kHz from the carrier, so as not to interfere with the digital sidebands.  The digital carriers are limited in power to about 20db (usually a db or two higher because there is an amplitude component present in the HD carriers) below the carrier power.  So, a 50,000 watt station like WABC's digital carriers are running about 500 watts in average power level.  Envelope detectors "decode" the HD carriers as a "hiss". 

When WABC on 770 kHz and WJR in Detroit on 760 kHz were both running HD at night, here in Cleveland, about 100 miles from WJR's non-directional signal, both WJR and WABC were unlistenable due to the hiss each put on the other.  I had a conversation with a WABC engineer several months ago, and he mentioned that even only 50 miles away from the WABC transmitter, listeners were complaining of the inability to hear WABC clearly at night, due to the WJR digital sidebands.

Within several months of commencing nighttime HD, with Citadel broadcasting owning both WABC and WJR, Citadel had WJR discontinue nighttime HD.  For the last several months, WJR has not been running the HD carriers even during the day.

It is looking like AM HD is going to go the way of what the Magnavox AM stereo system did 20 years ago.  Like Pete Seeger once wrote, "When will they ever learn...."

73,
Ted  W8IXY

[KF1Z]

DRM.

Many AM SW stations are broadcasting digital under their AM signals.

Under, over, around...whatever.

Been going on for a while now.

[Steve - WB3HUZ]

I'm almost positive DRM is NOT a cochannel system, that is it's either DRM or analog, but not both at the sametime on the same channel.

DRM.

Many AM SW stations are broadcasting digital under their AM signals.

Under, over, around...whatever.

Been going on for a while now.

[KF1Z]

I've decoded it here with "DReaM". (Not on 758khz, but up in the higher sw bands.)

On some, but not all....

Some may be a different HD digital scheme..

Makes for a funny looking signal....
The am analog still sounds ok, doesn't seem to bother it much.

[W2ZE]

Biting my tongue.....

I'm almost positive DRM is NOT a cochannel system, that is it's either DRM or analog, but not both at the sametime on the same channel.

Yes Steve, AM DRM is an all or nothing system.

Mike, W2ZE

[kenw2dtc]

W8IXY SAID:  "The digital carriers of AM HD extend about 18 kHz on both sides of the carrier.  So WABC's nominal occupied bandwidth runs from 752 kHz to 788 kHz."

I didn't know that.  Thanks for the information.

73,
Ken W2DTC

[Steve - WB3HUZ]

I refer you to the DRM standard, ETSI ES 201 98, specifically Appendix K. In all cases, but one, the DRM and analog are on different channels. Even in the half-channel case, the analog and DRM do not overlap. One could argue that the half-channel case qualifies as in-band, on-channel.

http://www.drm.org/uploads/media/ETSI_ES_201_980_v2.3.1.pdf

I've decoded it here with "DReaM". (Not on 758khz, but up in the higher sw bands.)

On some, but not all....

Some may be a different HD digital scheme..

Makes for a funny looking signal....
The am analog still sounds ok, doesn't seem to bother it much.

[WA1GFZ]

I seem to Remember Radio Moscow having crap off the side. When I had my Rhombic I loved moving right next to them and operating CW on 40. This would usually guarantee a commie contact.

[KF1Z]

I refer you to the DRM standard, ETSI ES 201 98, specifically Appendix K. In all cases, but one, the DRM and analog are on different channels. Even in the half-channel case, the analog and DRM do not overlap. One could argue that the half-channel case qualifies as in-band, on-channel.

http://www.drm.org/uploads/media/ETSI_ES_201_980_v2.3.1.pdf

I've decoded it here with "DReaM". (Not on 758khz, but up in the higher sw bands.)

On some, but not all....

Some may be a different HD digital scheme..

Makes for a funny looking signal....
The am analog still sounds ok, doesn't seem to bother it much.

Why my DRM (only) software would decode perfectly a digital signal with a very strong Analog AM signal riding on top of it ... I don't know....

But I must be wrong.........   

[Steve - WB3HUZ]

You may want to query the DRM people to see if their standard is out of date. Then you won't feel so bad.

All kidding aside, if you could post some tech specs or spectrum shots, it would be interesting. Also, was the analog audio and digital audio the same? If so, what, if any, delay was there between the two? How long did it take to transition from the analog to the digital (lock up time) and how quickly did the analog audio appear, if digital lock was lost?

[ve6pg]

...sometimes there are some weird sigs, on the mw band...last winter, i was hearing cw beacons on 537kc, as well as 1658kc...2 letter calls, i suspect those drift-net beacons i hear on 160. this past spring, i heard some kind of digi sigs (like packet), on 1615kc.....sk..

[N0BST]

The US does not use DRM on the AM band but a proprietary system developed by a company called Ibiquity.

Scott Todd

[W1AEX]

I hear the same thing on WTIC 1080 when I listen to it on an analog radio with a wide bandpass. The digital noise mixes right in unless I tighten things up with a filter. I love the HD quality, but it sure messes up the analog signal under some conditions. It looks like a pretty ugly signal among the standard AM broadcasts...

Rob W1AEX

[k4kyv]

The US does not use DRM on the AM band but a proprietary system developed by a company called Ibiquity.

That's one of the problems I have with it. That company was given a monopoly by the FCC, and every station must pay a highly inflated price for the IBOC generator, plus an annual licensing fee to use it.  Included in the cost of every receiver with IBOC capability is a licensing fee the receiver manufacturers must pay Ibiquity.

The trademark HD Radio® was designed to confuse the public and deceive people into believing that the radio system is somehow related high definition TV.  Supposedly "HD" originally stood for "hybrid digital".

I don't know what it sounds like on AM or FM because, like AM stereo, I have yet to see a receiver with the capability of receiving it.

[Pete, WA2CWA]

The trademark HD Radio® was designed to confuse the public and deceive people into believing that the radio system is somehow related high definition TV.  Supposedly "HD" originally stood for "hybrid digital".

I don't know what it sounds like on AM or FM because, like AM stereo, I have yet to see a receiver with the capability of receiving it.

My Sony AM/FM "HD Radio" sounds fantastic on FM. When you tune across the band and stop on a station that transmits in "HD", the receiver then locks on the digital piece, the quality of sound is greatly improved. I added a set of computer speakers along with a subwoffer, and now my old drifty stereo sits in a basement corner gathering dust. Just like digital TV, some FM stations give you some additional channels on one dial setting. Since I generally don't listen to the AM band, I haven't judged its performance there.

[Todd, KA1KAQ]

I get the loud hiss or swish sound some nights listening to 740 AM, but only on nights when the band is moving around. Never tracked it down, wonder if it could be the same station? Doesn't block the analog signal, it's just messy and annoying as hell.

[Steve - WB3HUZ]

That company: grew out of a company formed by Gannett, Westinghouse and CBS, called US Digital Radio Partners. It later merged with Lucent Digital Radio to form iBiquity. Large broadcasting companies were involved and supporting all along. Everyone went into this with their eyes open.

It's mere speculation that the term HD Radio was selected to confuse anyone.

[W1AEX]

I don't know what it sounds like on AM or FM because, like AM stereo, I have yet to see a receiver with the capability of receiving it.

Yah Don, in my opinion, the "HD" tag seems to be an intentional marketing ploy designed to confuse the public. It still seems to be struggling to catch the public's interest though.

On the AM side, unless the HD signal is really strapping, my HD receiver will fall back to the analog signal. As Pete said, the fidelity improvement over the analog signals is very dramatic. On the AM broadcast band an HD signal sounds very clean, no static, no fading, no phase distortion. Sadly, if any static, fading, or phase distortion exists, the HD signal will simply fall back over to analog. I've seen a few HD car radio systems, but don't know how well they function. My suspicion is that they probably don't do to well with HD on the AM broadcast band. On the FM side, however, it seems that HD reception is much easier to accomplish, and it sounds way better than standard FM, approaching CD quality. My Sony XDR-S3HD receiver is probably pretty primitive compared to what is out there now, but it actually works very well.

Rob W1AEX

[k4kyv]

But they should have done it like TV and let the stations that want to convert to digital run 100% digital, rather than that bogus business of running digital piggy-back on top of the analogue signal.  That would have been a good use for TV channels 5 & 6 for an expanded FM band.  The digital signals would be assigned to the expanded band, while the analogue signals would remain on the regular band.  A station could run both, on separate channels in the two bands.  If digital technology catches on, the analogue stations would eventually go dark, and digital stations could eventually move into the old band.

AM stations wishing to go digital would also be relocated to the expanded FM band, leaving the AM band analogue only.

The FM stations running HD are now trying to get the FCC to let them increase the power of the digital component to 10% of the total power (gee wizz!).  Wouldn't it make a lot more sense to run the digital signal at 100% of the licensed power?  Then maybe digital wouldn't result in a loss of coverage area.

If the conversion to digital TV and digital radio had been one coordinated effort, we wouldn't have the present hodge-podge mess, and digital radio might have actually captured the interest of the public.