Could this work?

[nd2023]

Can 2 50000 watt FM stations on the same frequency but about 80 miles apart which have the exact same analog programming also broadcast the exact same HD signal so that you could drive from station A to station B with no HD dropouts in the middle, 40 miles from each station? Let's assume that it's -10 dBc and each station by itself is dropout-free for 45 miles.

Or could station A broadcast the lower sideband and station B broadcast the upper sideband so that the HD signals don't interfere with each other? Would they reinforce each other in the middle, 40 miles from each station?

 

[RadeoEngineer]

The bigger issue would be the interference to each other's analog signals.

 

[Len14043]

We had 2 stations broadcast the some material on 97.7 near Cincinnati. The stations were located about 65 miles apart and attempted to serve the greater Cincinnati area. The capture effect causes a slightly stronger signal on the same frequency to attenuate the weaker signal. When both stations have a signal strength difference of less than about 10 dB, the result is a hiss on the stronger signal which gets progressively louder as the difference in signal strength of the co-channel signals becomes less. Picket-fencing also occurs. Basically, a zone of interference exists somewhere between both signals - even if the program material is identical. I'm not sure how the capture effect would manifest itself if you had 2 identical digital signals that were strong enough to individually be decoded. I suspect there would be a small area where the digital signals would fail to decode, but I believe the area of interference would probably be less then that of the analog signals. If, like you suggested, o station digitizes the lower side band while the other signal digitizes the upper band, that may work provided the stations were not too far apart. Another possibly would be to have asymmetrical sidebands in which one station used -14 db on one sideband and -10 db on the other side band, while the other station did the reverse. This way you could have robust digital signals while overlapping the digital zones of interference.

 

[Ai4i]

A better way would be to do as the Europeans have done for many years in analogue. The numerous stations are on different frequencies but send out identical RDS ID codes, the listener sets their radio to find the station (say, BBC-3) and the radio scans for the one with the most quieting.

 

[Play Freebird]

A better way would be to do as the Europeans have done for many years in analogue. The numerous stations are on different frequencies but send out identical RDS ID codes, the listener sets their radio to find the station (say, BBC-3) and the radio scans for the one with the most quieting.

This is called "AF switching" and it works quite well if the simulcast stations have overlapping 54 dBu contours. I have a Delco prototype car radio which hands off very cleanly (within 100 milliseconds or so) and it's hard to tell when the switching actually takes place. Whenever I've rented cars in Europe, they've been equipped with AF-capable radios and I must say it's a pleasure to use.

Unfortunately, due to the several second buffering delay, AF switching is impractical for HD Radio (in all-digital mode) unless the receiver incorporates two parallel front ends and decoders. Another giant step backwards.

 

[ajc_trw]

Can 2 50000 watt FM stations on the same frequency but about 80 miles apart which have the exact same analog programming also broadcast the exact same HD signal so that you could drive from station A to station B with no HD dropouts in the middle, 40 miles from each station? Let's assume that it's -10 dBc and each station by itself is dropout-free for 45 miles.

Or could station A broadcast the lower sideband and station B broadcast the upper sideband so that the HD signals don't interfere with each other? Would they reinforce each other in the middle, 40 miles from each station?

This type of thing is being done in the Los Angeles market between KDLD 103.1 Santa Monica and KDLE 103.1 Newport Beach. The two signals are synchronized so radios between the two stick would receive an identical signal and sum them, in theory. In practice Long Beach has never gotten any better than a fuzzy signal. I interned for Mars-FM in 1991 and drove between Newport Beach and Santa Monica and can say theory is far from practice.

http://en.wikipedia.org/wiki/KDLD

 

[Gatekeeper007]

Motorola did this in to way radio in the 80's and 90's on analog and it worked very well so long as the transmitters use were exactly the same make, audio settings, and power levels controled along with their using WWV as a constant at all locations to alignment the same. Now a days WWV would not be nessary as better methods are used for signal compairson today but it is still nessary to compare signals so the midway point would not have picketing, fading, or signal burp problems but if done correctly should work good.

 

[ve3jf]

Yes, this could work fine, as far as the digital signal is concerned. Since it uses OFDM modulation, the signals will reinforce constructively, provided that the two transmitters are well-synchronized (easy, with GPS) and there are no reception areas where the relative delay between the signals exceeds 75 microseconds.

The problem, as other posters point out, is that you can't have seamless coverage for the digital signal without having overlapping coverage for the analog, and in the overlap area, the analog reception will be seriously degraded. Basically, you're creating multipath, which OFDM thrives on, and analog FM hates. Just another shortcoming of the "hybrid" IBOC system...