Now that analog is going away -especially after 06/12, I have to wonder why most, if not all TV stations put out a horizontal TV signal pattern to maximize coverage area if there's no interference in the area. For example, most of the Boston area TV stations appear to be non-directional and give off a great signal over a wide area. But in the Providence area, for example, chs, 12 and 64 are non-directional and have a fairly wide signal range, but chs. 10 and 6 are directional and have a weak signal to the northeast (facing Boston) for some reason I can not understand - there's no interfering channels in the Boston area. Is it cheaper on the power bills to broadcast in a directional pattern? And what's the difference between broadcasting in a horizontal,vertical, and circular pattern? Please instruct me.
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DIRECTIONAL DTV SIGNALS
- Thread starter alg2468
- Start date
You're mixing two terms together. There's directional patterns and then there's polarization. Let's start with polarization.
Draw yourself a wave on a sheet of paper. Now hold that paper horizontally. This is what horizontal polarization looks like. This is why TV antennas are horizontal. Now hold the paper vertically. This is what vertical polarization looks like. This is why FM antennas are vertical rather than horizontal, because many FM stations have some vertical component to them. Now roll the paper up so it looks kind of like a paper towel tube. This is close to what circular polarization looks like, but not totally. You'll see that it has elements of both horizontal and vertical. Check out the diagram on this page: http://en.wikipedia.org/wiki/Polarization Horizontal and vertical are two types of linear polarization.
As far as directional patterns go, in many cases, a station may choose not to broadcast a lot of power in the direction where they don't have many viewers, as would be the case in Boston. Of course, 180 kW (in the case of WJAR) is not really a huge null. That's still plenty of power to receive a signal like that.
Other stations may have antennas side-mounted on the tower, which means there's little point in beaming a lot of power back in toward the tower. Stations may use a composite array of several antennas to come up with a side-mounted pattern which works for them, which will result in some odd nulls in some directions.
I'll let an actual engineer chime in here, but that's a bit of an intro.
- Trip
Draw yourself a wave on a sheet of paper. Now hold that paper horizontally. This is what horizontal polarization looks like. This is why TV antennas are horizontal. Now hold the paper vertically. This is what vertical polarization looks like. This is why FM antennas are vertical rather than horizontal, because many FM stations have some vertical component to them. Now roll the paper up so it looks kind of like a paper towel tube. This is close to what circular polarization looks like, but not totally. You'll see that it has elements of both horizontal and vertical. Check out the diagram on this page: http://en.wikipedia.org/wiki/Polarization Horizontal and vertical are two types of linear polarization.
As far as directional patterns go, in many cases, a station may choose not to broadcast a lot of power in the direction where they don't have many viewers, as would be the case in Boston. Of course, 180 kW (in the case of WJAR) is not really a huge null. That's still plenty of power to receive a signal like that.
Other stations may have antennas side-mounted on the tower, which means there's little point in beaming a lot of power back in toward the tower. Stations may use a composite array of several antennas to come up with a side-mounted pattern which works for them, which will result in some odd nulls in some directions.
I'll let an actual engineer chime in here, but that's a bit of an intro.
- Trip
tripinva said:
I know it is hard to believe, but WJAR's signal in this direction is really not that good. I'm not just some person that has no experience with antennas and/or setting up a DTV box either. I've been a ham for over 10 years, and actually gave a short presentation at one of our local ham club meetings on how to set up a DTV box recently. That location of the meeting, just using a small indoor antenna, I had very similar results to what I have here at home. The Boston stations came in fine, and WPRI, WJAR, and WLWC came in fine, but no sign of WJAR, WLNE, or WSBE.
With the CM 4228 here at home, I get almost 100% signal from all of the Boston stations (except not enough signal to decode WYDN-DT 47, which is also a directional signal, not sending much SE). The antenna is probably about 35-40 feet off the ground, and is on a rotor.
I'll be really interested to see what the difference is once WJAR moves to the top of their tower.
I suspect the WJAR antenna is side-mounted and it's probably on the "Rhode Island" side of the tower. Moving it to the top would likely do a lot to help the issue by getting the tower out of the way. Actual engineers should chime in, though, before I look like too much of an idiot. 
- Trip
- Trip
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necrat123
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tripinva said:I suspect the WJAR antenna is side-mounted and it's probably on the "Rhode Island" side of the tower. Moving it to the top would likely do a lot to help the issue by getting the tower out of the way. Actual engineers should chime in, though, before I look like too much of an idiot.
- Trip
Being a upper UHF channel is tough for any station. WJAR-DT is going to remain directional as a top mount, focusing the energy towards Rhode Island, their main focus. WLNE is directional in that direction as well. WJAR-DT could not move back to 10 without being directional to protect WTNH-DT also on 10. If they went back to 10, their directional pattern would null in the direction of ... Providence and all of Rhode Island.
Stations go directional for two primary reasons. 1) to focus more RF energy in a certain direction and/or 2) to protect another station.
i.e. WNAC-DT 54 was directional towards WEDN 53 in Norwich, CT.
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