IBOC Hash In June

[Shellanswerman]

A previous post indicated that WBZ-AM and WMKI-AM were running their IBOC (with accompanying hash) after 6:00 pm. At the time, there was no AM IBOC hereabouts before 6:00 am with the switch to EDST. Now, in June, the month with the most daylight hours, both WBZ-AM and WMKI-AM in Boston are running their digital transmitters starting at 5:00 am. And here's something strange...at least last night (06/01), WMKI did pattern-switch/IBOC off at 8:15 pm...WBZ-AM stayed with it until 8:30 pm. Each has a transmitter at almost the same latitude! (Just for fun, I tried NYC's WLIB-AM to see if it was RECEIVING hash from Rochester's WHAM, but neither was coming in well at sunset.)

 

[DanStrassberg]

> A previous post indicated that WBZ-AM and WMKI-AM were
> running their IBOC (with accompanying hash) after 6:00 pm.
> At the time, there was no AM IBOC hereabouts before 6:00 am
> with the switch to EDST. Now, in June, the month with the
> most daylight hours, both WBZ-AM and WMKI-AM in Boston are
> running their digital transmitters starting at 5:00 am. And
> here's something strange...at least last night (06/01), WMKI
> did pattern-switch/IBOC off at 8:15 pm...WBZ-AM stayed with
> it until 8:30 pm. Each has a transmitter at almost the
> same latitude! (Just for fun, I tried NYC's WLIB-AM to see
> if it was RECEIVING hash from Rochester's WHAM, but neither
> was coming in well at sunset.)
>
The line of demarcation where average sunset in June is at exactly 8:22:30 PM EDT must slice through the middle of greater Boston. On one side of that line, AMs can remain on day power/pattern until 8:15 PM; on the other side they can go till 8:30 PM. And the line does not run from north to south either, because both lattitude and longitude enter into the time of sunset. At any latitude, the length of daylight on any given day will be the same, but the farther west you go, the later sunrise and sunset will both occur. So does the line go from southeast to northwest or southwest to northeast? Good IQ-test question. I think the answer is southwest to northeast, but I'm not sure. If I'm correct, though, WBZ ought to be switching off IBOC at 8:15 in June.

A curiousty is that WBIX's two transmitter sites, though only about three miles apart and almost exactly at the same longitude may be on opposite sides of the line. Fortunately, I think WBIX is completely legal if its uses its night facilities during the day. The converse is not true, however. There are some stations in the Boston area that, because of pattern differences, can't legally use their night facilties by day even though they run at lower power by night. That is true of WBNW, which interferes with the 1110 station in Salem NH if it uses its 1 kW-N signal during daylight hours. WBNW's 5 kW-D signal is sharply nulled toward Salem. The night signal is not.

 

[HD_Ready]

It makes for good digital DX'ing, I will have to check the usual IBOC signals from other markets some morning or evening.

(I picked up WBZ-HD while in the Carolinas)