Adjacent channel interference

Tim58hsv · 08-21-2009, 07:39 PM

Is there such a thing as adjacent channel interference in this digital age? TVFool has warnings about adjacent channel interference but does it really exist anymore?

Adjacent channels were a big no-no for analog transmissions due to the interference they'd cause to one or the other channel, but with digital it doesn't seem to be a problem.

Here in the Dayton, Ohio tv market we have lots of adjacent channels and it's no problem at all, even when one channel is at the max power and the other isn't.
A good example from the Dayton market...

WDTN ch. 2 / rf ch. 50 / 1000kw
&
WKEF ch. 22 / rf ch. 51 / 128kw

With both transmitting antennas being located at the same antenna farm, one would think that would cause lots of adjacent signal problems but it doesn't.
I'm thinking adjacent channel interference is a thing of the past.

Yes?
No?
What say ye?

Trip · 08-21-2009, 08:00 PM

If stations are co-located, adjacent channel interference isn't a concern. The problem is when there's space between them and they're adjacent. For example, lots of people in the Chambersburg PA area had problems with channels on 38 and 40 in Baltimore when WJAL (which is much closer) signed on channel 39.

- Trip

Tim58hsv · 08-22-2009, 09:06 AM

Quote:

Originally Posted by Trip

If stations are co-located, adjacent channel interference isn't a concern. The problem is when there's space between them and they're adjacent. For example, lots of people in the Chambersburg PA area had problems with channels on 38 and 40 in Baltimore when WJAL (which is much closer) signed on channel 39.

- Trip

That's interesting. With Chambersburg and Baltimore being 70 miles apart I'd imagine the signal from Baltimore would be extremely weak in Chambersburg and it wouldn't take much to wreck it. Is that about right, Trip?

BTW
Dayton has an adjacent channel with Cincinnati (WRGT rf 30 & WXIX rf 29. 42 miles apart) and there's no adjacent channel problems there that I've seen or heard of.

Piggie · 08-22-2009, 10:57 AM

While in some reception locations, non collocated adjacent channels can cause interference. However the FCC has spoken and set distance and power levels that deem acceptable. It's not perfect.

In my opinion their adjacent channel rules work a lot better than their co-channel rules. In other word since nothing is perfect unless there is only one station on a channel in the universe, then fewer people are bothered under the current adj-channel rules than those like me that are plagued by the FCC's legal co-channel rules.

end of the road · 11-18-2009, 03:06 PM

WTFX-29 (RF42) in Philadelphia and WMPT-22 in Annapolis are by my calculation only 102 miles apart. I can get neither signal. How could this happen? Also WTUB-24 in Baltimore is on Ch 41. I can't get it either.

DTVuser2009 · 11-18-2009, 03:14 PM

I looked hard at TV fool's results. i found that on 'ajascent channel' and 'co-channel' warnings it was because the channel in question has the same real channel number as a station, perhaps well over 100 miles away.

Channel 30, KET here, is also some other channel using the same RF channel number but well out of the range of my capabilities. it may only matter if you have two close-distance channels using the same number, which could make it near-impossible to get either one. think of it as an IP-Address conflict on a network. two computers using the same IP can't connect.

Jim In Seattle · 11-18-2009, 03:40 PM

Quote:

Originally Posted by Trip

If stations are co-located, adjacent channel interference isn't a concern. The problem is when there's space between them and they're adjacent. For example, lots of people in the Chambersburg PA area had problems with channels on 38 and 40 in Baltimore when WJAL (which is much closer) signed on channel 39.

- Trip

-----------------------------------------------------------
Hi Trip!
In my neighborhood (literally), the Komo-4 (38) and Kiro-7 (39) towers are physically about 600 feet apart. I'm to the side of them so for practical purposes they are on the same compass bearing.

KIRO upped their antenna height and power last summer (I can now receive them directly) and hopefully KING will do the same, soon. Should I anticipate any problems when KING follows suit? Next question: what does that interference 'look' like? My guess is the same blank screen as no signal or overload! HA!

Jim


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