What are Co-channel and Ajacent channel warnings?

#1
i am wondering. about two channels i got are showing one of more of those tiny flags yet they come in fine? they're the ones coming in the strongest too lol! PBS is one of em.
 

Don_M

DTVUSA Member
#4
If you're referring to the notations next to station listings in a TVFool report, the overwhelming majority of co- and adjacent-channel warnings can be safely ignored. The reports list them even if there's no chance that the weaker station of each pair is receivable -- i.e., below a noise margin (NM) of maybe -10 dB or so.

Looking first at co-channel interference, let's say you have a local channel with a 50+ dB NM, and another station a hundred miles away broadcasting on the same channel, but with a projected NM of -20 db. The 70+ dB difference means the local station's signal is stronger than the more distant station by at least seven orders of magnitude -- 10 million times. That's an extreme example, perhaps, but a lot of these station pairs have signal-strength differentials in the five- and six-orders range.

Adjacent-channel assignments used to be a big deal in analog broadcasting, particularly three decades ago when UHF tuners were a lot less precise than they are now. In addition, digital signals are less prone to cause interference to broadcasts on adjacent channels because of their differing nature. (Calling Piggie: Got any screenshots comparing analog and digital signal analyzer traces? They'd be educational about now!) Where interference might be a possibility, the FCC typically orders one of the stations (usually the low-power outlet) to install an additional filter at the transmitter to ensure it doesn't happen.

FCC regulations also sharply reduce the incidence of adjacent-channel interference by specifying how much distance is allowable between two such transmitters. The regs are involved, but to oversimplify, the two stations' antennas may be located at the same place, or within maybe 10-12 miles of each other. If that's not possible, they must be separated by much greater distances -- in most cases, 68+ miles (for UHF) and well over 100 miles (for VHF).
 
#5
Now maybe someone could explain what 'LOS' '2Edge' and 'Tropo' means on the report. i got at least one channel to stay at home from 60+ miles away and it is listed as 'Tropo' but at 4PM i doubt tropo ducting is the cause or reason for that report flag.

All of my 'new' channels i've gotten with a triple-amp setup are in the 'extreme measures' but are as strong now as the usual ones i got prior to the transition.
 

Tim58hsv

DTVUSA Member
#6
Now maybe someone could explain what 'LOS' '2Edge' and 'Tropo' means on the report. i got at least one channel to stay at home from 60+ miles away and it is listed as 'Tropo' but at 4PM i doubt tropo ducting is the cause or reason for that report flag.
LOS means Line of sight. You should be able to get it.

2edge means there are obstructions such as hills in the way. Not easy to get but doable.

Tropo means the signal is there but it takes extreme measures to recieve it.
 

Don_M

DTVUSA Member
#7
LOS = Line of sight. This means the transmitting antenna should be visible through a sufficiently powerful pair of binoculars or a telescope at a given location as long as 1) there are no vertical obstructions (trees, buildings) in the way, and 2) humidity/air quality is low/good enough to allow for visibility at that distance.

"1-edge," "2-edge" = Signal diffraction (bending, if you like), typically over ridge tops or mountaintops. The taller the ridge(s) or mountain(s) relative to your location, the greater the diffraction and, usually, the weaker the signal. The 1 and 2 refer to the number of such obstructions.

Tropo = Tropospheric ducting, but you knew that judging from your post. TVFool reports are based on a bunch of algorithms; the predictions are sometimes off, just like your not-so-favorite local weather forecaster misses the mark at times. IMHO, what's amazing is how often TVFool is dead-on accurate!

Oopsie! Got beaten to the punch again. Sorry, Tim.
 
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#8
All i know is that i had 15 channels that i could barely manage to keep a solid lock on 100% now i have 20 that are sticking around and not just temporary mid-morning channels.

WAZE-DT is best from 4PM to 8PM but if i turn on a fan or the refrigerator comes on and the signal is low, it goes out completely. but having it for a few hours is better than never having it at all. first time i've watched Friends since 2008. without a program guide i cannot see what other shows are on and Friends used come on in the wee hours of morning, now it's advertised and shown at 6PM and 9PM (barely saw that one, a repeat but the signal was barely there but there enough to see that it was on again)

The shows i watched were:

1. Friends, listed above and still on

2. George Lopez (came on sometime at night, i think 10PM)

3. The Dead Zone (Saturday)

4. a double-episode block of The Ghost Whisperer (Friday, but CBS WEVV is airing the new season just saw the promo :) )

5. Roseanne, Cosby Show, Good Times, and The Jeffersons, (weekday mornings but i work during that time so i am unable to check)

they used to air King of the Hill and Family Guy each night also but Friends took over that slot, so it has either moved or has gone completely and i still catch those on Fox during Animation Domination-- at least until Football once again takes over.
 
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