MW question from MW newbie

[glimmer twin]

I don't really do any MW dx'ing but I do listen to a station from ST Joseph, MO on weekends when they have Old time radio shows overnight. I noticed that when I tune them in (KFEQ 680) there is a lot of noise in the upper side band but not in the lower side band. When I tune them on my SDR I see what looks like a digital signal centered on 685 with nothing where a carrier would be but digital hash 5 khz either side of the what for sake of a better term I'll call the "non carrier". Is this IBOC ,  the digital thingy I've heard of but obviously don't understand? I see other stations with digital "hash" in one or the other sideband. Maybe I'm seeing something in 690's LSB & 680's USB that appears to be centered on 685. The 2 digital hash thingies seem like they are of different strengths. One other question... if this is IBOC that I am seeing does it suck as much as I think it does? because I really think it sucks.

[skeezix]

IBOC it is.

In hybrid mode (AM+digital), analog audio is +/- 5 kHz. From +/- 5 kHz to +/- 10 kHz are the secondary digital sidebands and from +/-10 kHz to +/- 15 kHz are the primary digital sidebands.

We have a couple of locals on IBOC. The biggest, WCCO 830, is a 50 kW flamethrower about 15 miles from me.

So what that means for WCCO:
AM: 825-835 kHz (carrier 830 kHz)
Secondary digital: 820-825, 835-840
Primary digital: 815-820, 840-845

As far as jamming on 680 USB, I believe you're hearing a station on 670 and their primary upper digital sideband. If it is 670, you should see the noise band at 660 LSB. If you have a loop, rotate it and you should see them fade in/out together.

And yes, it does suck. I have a HD receiver and can pick up 830 in HD. Its sounds like a crappy low-bit rate Internet stream. It does better at jamming than it does at providing the quality signal they claim it can. Even if I put 830 in my loop's null, 820 & 840 are impossible for DX. I can pick up a station on each, but no way for anything else. And now WDGY 740 started IBOC. But they're only a daytimer, so their jamming is limited.

 
From Ibiquity, the creators of this mess:
http://www.ibiquity.com/i/pdfs/Waveforms_AM.pdf

Other info:
http://hackipedia.org/Encoding/Modulation/AM%20(radio)/html/AM%20Hybrid%20IBOC%20Parameters.htm
http://radiomagonline.com/digital_radio/hd_radio/iboc_mask_compliance_1011/?cid=mostpopb2

[glimmer twin]

Thanx Skeezix. As I said I don't really do much, or in fact any, MW dx'ing although I always intend to but never get around to it. I am able to avoid the IBOC mess on 680 KFEQ by tuning , with my trusty dog walk PL 660,  with the synchronous detector on the LSB. I only listen to MW to hear the OTR shows on Sat & Sun as I walk the hound & it requires constant adjustment of the radios angle in relation to St Joseph which is NW of me. Last night was the first time I really examined the MW spectrum with my SDR-IQ & I was truly appalled at what a mess it appears to be.