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IBOC Co-Channel Observation
- Thread starter K6JHU
- Start date
badjef said:
I started in 1977 on an old RCA 811K console, with a 300-400 ft LW WBAP TX 820 was a semi regular here in Ma. I got KSL 1160 Utah the first night I ever DXed with that radio just by waiting on the clear channel until KSL faded up and then back down. I had a list of not too many pages of American AM stations in (I think) a Popular Electronics mag about AM DXing I just sat there on a clear until it came in.
Right now LSB on 1020 is at 60 db, carrier is at 70 db on 1030 and USB on 1040 is at 50+ db. I am about 40 miles from WBZ and this is from my receiver meter. Even though lower is a little bit higher on the meter the whoosh is about the same. This is pretty consistent for WBZ here, the upper sideband is a little bit higher usually although they change in relation to each other at times. The sidebands levels change while the carrier level doesn't, strange.
D
diymedia
Guest
iyiyi said:
"Data constellation?" That makes HD sound like something out of TNG. The digital signal are sidebands relative to the analog signal, which anchors the center frequency of the hybrid broadcast. I'll admit that HD is a clever engineering feat, but man, come on.
Read the spec. Full digital still requires a "vestigal" carrier as the what the data references "to".
Haven't yet encountered a SSB iboc, but then what's been described is an asymmetric response or
reception of what could have been perfectly balanced sidebands at input to the ATU.
Analog tuned (old fashioned) hardware type radios seldom had (or retained) perfectly tuned IF response, meaniing it was common to have a receiver where the stronger AM stations always sounded "better balanced" in audio on the upper or lower sideband (for that radio).
Similarly, the "linearity" and efficiency of any transmit antenna runs high to low through an ideal midppoint defined by wavength, and at this point there's no escaping that tuning of huge physical LC networks change.
Could be entirely a little bit of lopsided response, and already have some "english", thrown to make sure it's not even worse
for decode, though perhaps better balanced form the perspective of measured response.
In part 15 AM operation, the effects on bandwidth from the extreme shortening of the antenna makes it hard
get both sidebands the same, and for the most part they're just NOT.
The lower sideband always seems to have better and more balanced hig-end response on most of my radios.
Tuning and loading effects have a lot of influence on sideband balance.
It's much like shooting water at high speed through a series of holes in line with each other.
The holes had all better be the same size or a lttle larger than the column of water you started with, and they
had better line up pretty damn good.
Good news to rbuce: the only 50 kw Chicago zombie (for now) is WBBM.
Others were too embarassed to continue sounding "like that'.
There's still 620 milwakee at ? power, and in Chicago 1390 and 1690 at "lower powers" still on iboc.
Haven't yet encountered a SSB iboc, but then what's been described is an asymmetric response or
reception of what could have been perfectly balanced sidebands at input to the ATU.
Analog tuned (old fashioned) hardware type radios seldom had (or retained) perfectly tuned IF response, meaniing it was common to have a receiver where the stronger AM stations always sounded "better balanced" in audio on the upper or lower sideband (for that radio).
Similarly, the "linearity" and efficiency of any transmit antenna runs high to low through an ideal midppoint defined by wavength, and at this point there's no escaping that tuning of huge physical LC networks change.
Could be entirely a little bit of lopsided response, and already have some "english", thrown to make sure it's not even worse
for decode, though perhaps better balanced form the perspective of measured response.
In part 15 AM operation, the effects on bandwidth from the extreme shortening of the antenna makes it hard
get both sidebands the same, and for the most part they're just NOT.
The lower sideband always seems to have better and more balanced hig-end response on most of my radios.
Tuning and loading effects have a lot of influence on sideband balance.
It's much like shooting water at high speed through a series of holes in line with each other.
The holes had all better be the same size or a lttle larger than the column of water you started with, and they
had better line up pretty damn good.
Good news to rbuce: the only 50 kw Chicago zombie (for now) is WBBM.
Others were too embarassed to continue sounding "like that'.
There's still 620 milwakee at ? power, and in Chicago 1390 and 1690 at "lower powers" still on iboc.
N
nocomradio
Guest
Not fully understanding all the technical side of IBOC or HD AM, I can just add one observation:
DX'ing since the 70's, I've never heard a band so noisy now. Not just from local noise sources like CFL's or electrical interference, but that persistent "jet whine" noise all across the band that appeared when IBOC was introduced and has yet to go away. It really is annoying.
DX'ing since the 70's, I've never heard a band so noisy now. Not just from local noise sources like CFL's or electrical interference, but that persistent "jet whine" noise all across the band that appeared when IBOC was introduced and has yet to go away. It really is annoying.
Tom Wells;
8VSB ATSC HDTV has a 2 microsecond "pulse" the receiver PLL uses to synch data. Where can I view the "spec" showing a "vestigial carrier" component in a pure digital HD RADIO signal? While we're on the subject, where may I view any information showing a vestigial carrier in an ATSC 8VSB HDTV signal? Also, symmetrical MW hybrid HD radio digital carriers might be expected to appear at equal amplitudes on both upper and lower "sidebands". These HD carriers should both be found 20dB below the analog carrier level. Thanks!
8VSB ATSC HDTV has a 2 microsecond "pulse" the receiver PLL uses to synch data. Where can I view the "spec" showing a "vestigial carrier" component in a pure digital HD RADIO signal? While we're on the subject, where may I view any information showing a vestigial carrier in an ATSC 8VSB HDTV signal? Also, symmetrical MW hybrid HD radio digital carriers might be expected to appear at equal amplitudes on both upper and lower "sidebands". These HD carriers should both be found 20dB below the analog carrier level. Thanks!
R
rbrucecarter5
Guest
iyiyi said:
Thanks - we are all professionals here.
I'll check out virtual engineer. I am always interested in scientific observations.
Sorry - but there would be no other source of noise. The sideband pair couplings were uncanny and very obvious. I know that is what they were because HD sidebands do sound slightly different than random static. A trained ear can hear patterns. The noise floor out there was extremely low. There is NOTHING around to generate RF. It is spooky to turn on a radio and have almost every frequency blank. Definitely not in the experience of most people. The sideband pairs from closer HD stations were more pronounced. KOA was faint, but the sidebands were anything but faint! There is something about the digital nature of the sidebands that is very tenacious. What was strange to me were the sideband pairs that were not present. You would think the sideband pairs of KFI would have been there, but I learned after the fact that KFI had a tower down - maybe they weren't running it. The number of HD stations is low enough that it is possible to guess who the sideband offender is without too much fear of ambiguity. I did try for the sideband pair of WOAI. I can't be sure. It was a lot closer, but also a lot higher in frequency. Which seems to be another trend. Whatever makes the sidebands propagate like that seems to be limited to lower parts of the band, which I guess is not too surprising given that is true for analog AM, too.
I'd definitely like to get out there with an HD radio, but that was a special circumstance - my daughter had figure skating competitions in Denver. I really don't have any reason to go through that remote part of NM very often. But I if do, I'll be loaded with HD equipment because the prospect of 1000 mile HD AM digital would be exciting to everybody!
Incidentally, I did have occasion to try the sideband pair reception on I-40 rest areas on a trip to LA. They might have been there as I got further west, but I cannot say it was reliable. Certainly when I took side trips in Arizona to remote locations, there was no trace of them - until it got late in the afternoon. The sideband pairs emerged with a vengeance, long before the analog part appeared.
rbrucecarter5 said:
The prospect of getting AM HD reception more than 1000 feet from the transmitter is equally as exciting. It takes a lot more than a buzz to get HD reception (and it also takes a lot more than a buzz to get drunk, but that's another story). The analog is 20 dB higher than the HD, and I doubt the propagation method is that selective that it will notch out the analog while letting the IBUZ through.
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