As I mentioned in the “HD BOARD HAS CHANGED” thread, up until this past weekend—I have not noticed AM IBOC HD radio interference on clear channels at night... Not until Thanksgiving evening in the northeast suburbs of Cincinnati when I happened on 1120 KMOX St Louis obviously transmitting in HD mode just after 6PM EST. The culprit was clear, as the distinct IBOC “hash” was apparent on 1110 and 1130, and “I-buzz” was well audible on 1100 WTAM Cleveland and 1140 WRVA Richmond (both with strong and stable signals at the time). The IBOC carriers were switched off and the interference promptly ceased at 7PM EST.
I discovered this while checking out the exceptional radio in a family member’s new vehicle. Upon investigation, I learned the only possible source of outside electrical interference might have been a buried perimeter “dog fence”. I doubt that was a factor, as the effects were limited to the frequencies and stations I mentioned. Even second-adjacent stations to local Cincinnati IBOC-equipped 700 WLW (680 WPTF Raleigh, 720 WGN Chicago) and 1530 WCKY (1510 WLAC Nashville) were clearly received since LOCAL HD transmissions had ended every evening at 5:30PM local time.
I was not able to check at those periods on the evenings of 11/24 and 11/25 and noticed no IBOC carriers later on those dates. I felt this to be a fluke—possibly a “timing malfunction” on a holiday evening at KMOX.
I’m a Chicago Bears fan—they were playing the New England Patriots this evening (11/26), so I tuned in 1030 WBZ Boston just after 6PM EST to get an update on the game... And guess what I discovered? Not only KMOX (again in IBOC)—but also 1030 WBZ Boston transmitting for one hour in HD mode from 6PM to 7PM EST—well past local sundown in BeanTown. I quickly powered down the “dog fence”, swept the yard with a battery-operated CC Radio Plus and verified a “clean” outdoor listening area.
The effects from KMOX were identical to those described on 11/23—mildly pesky but very much present on the second adjacent channels. KMOX IBOC can do little practical damage to its first-adjacent channel neighbors 1110 WBT Charlotte and 1130 WBBR New York at that location since Cincinnati is well within the directional nulls of both.
WBZ was quite a different story. BOTH first-adjacent channels to WBZ (1020 KDKA in nearby Pittsburgh and 1040 WHO Des Moines) place very good signals into the Cincinnati area (KDKA is the second-closest “clear” to Cincinnati yet well beyond any groundwave conflict). IBOC “hash” at times nearly equaled the audio level of its adjacent neighbors. WHO was just getting its nighttime signal “giddy-up”, so the effects on its audio were more degrading. ONLY when WBZ went into a “deep fade” did very-objectionable interference subside. To speculate that the presence of WBZ IBOC carriers made both KDKA and WHO un-listenable to the “typical Joe” would not be an exaggeration.
This was only a “layperson’s” observation—no costly spectrum analyzer or field strength meter involved... Just my decent pair of ears and a good ’07 Chrysler minivan radio.
Now the question... Anyone know about some coordinated test? Any observations from elsewhere on other channels?
I discovered this while checking out the exceptional radio in a family member’s new vehicle. Upon investigation, I learned the only possible source of outside electrical interference might have been a buried perimeter “dog fence”. I doubt that was a factor, as the effects were limited to the frequencies and stations I mentioned. Even second-adjacent stations to local Cincinnati IBOC-equipped 700 WLW (680 WPTF Raleigh, 720 WGN Chicago) and 1530 WCKY (1510 WLAC Nashville) were clearly received since LOCAL HD transmissions had ended every evening at 5:30PM local time.
I was not able to check at those periods on the evenings of 11/24 and 11/25 and noticed no IBOC carriers later on those dates. I felt this to be a fluke—possibly a “timing malfunction” on a holiday evening at KMOX.
I’m a Chicago Bears fan—they were playing the New England Patriots this evening (11/26), so I tuned in 1030 WBZ Boston just after 6PM EST to get an update on the game... And guess what I discovered? Not only KMOX (again in IBOC)—but also 1030 WBZ Boston transmitting for one hour in HD mode from 6PM to 7PM EST—well past local sundown in BeanTown. I quickly powered down the “dog fence”, swept the yard with a battery-operated CC Radio Plus and verified a “clean” outdoor listening area.
The effects from KMOX were identical to those described on 11/23—mildly pesky but very much present on the second adjacent channels. KMOX IBOC can do little practical damage to its first-adjacent channel neighbors 1110 WBT Charlotte and 1130 WBBR New York at that location since Cincinnati is well within the directional nulls of both.
WBZ was quite a different story. BOTH first-adjacent channels to WBZ (1020 KDKA in nearby Pittsburgh and 1040 WHO Des Moines) place very good signals into the Cincinnati area (KDKA is the second-closest “clear” to Cincinnati yet well beyond any groundwave conflict). IBOC “hash” at times nearly equaled the audio level of its adjacent neighbors. WHO was just getting its nighttime signal “giddy-up”, so the effects on its audio were more degrading. ONLY when WBZ went into a “deep fade” did very-objectionable interference subside. To speculate that the presence of WBZ IBOC carriers made both KDKA and WHO un-listenable to the “typical Joe” would not be an exaggeration.
This was only a “layperson’s” observation—no costly spectrum analyzer or field strength meter involved... Just my decent pair of ears and a good ’07 Chrysler minivan radio.
Now the question... Anyone know about some coordinated test? Any observations from elsewhere on other channels?
I hope, this is what you are looking for: