OTA Antenna Setup

[SayWhat?]

Here's my situation. I'm located between 3 DMAs as indicated on the plot below.

To the west is my Primary DMA with the transmitters scattered across about 40 degrees or more. Most of them are within 50 miles, but one major station is about 80 miles. That one is on VHF-Hi, while the rest are UHF.

To the northeast is DMA 2 at roughly 65-75 miles and mostly either VHF-Hi or UHF.

To the southeast is DMA 3 at a little over 100 miles. One station is VHF-Lo while the others are either VHF-Hi or UHF.

With my current antenna (similar to this: http://www.radioshack.com/product/index.jsp?productId=3808570), mast mounted pre-amp and a rotor, I can:


usually get stations from DMA 3 in the early morning, but not any other time.

almost always get stations from DMA 2 except in bad weather.

get stations from DMA 1 clear in most conditions except the one that's VHF-Hi. It comes in clear about 75-80% of the time, but will flake out frequently even in what should be normal conditions.


Of course you have to rotate and can only get one DMA at a time.

What I hope to do is find a way to get all 3 DMAs with some sort of dependability. I was thinking about using 3 antennas, one pointed in each direction, but how would I get all three combined to one input cable for the TV? Do 3 way splitters work in reverse?

Another thought was to use one of the 360° disk/pancake units, but they don't seem to claim much range (about 40-50 miles).

The current antenna is about 35' AGL, but my planned set-up will get me closer to 50' AGL. Currently, there is a tree partially blocking the SE view, but I'll be clear of that where I'm planning to re-locate the mast.


http://www.dbstalk.com/attachment.php?attachmentid=25764&d=1307868113

[P Smith]

Theory tell us about combining antennas, it would make it ineffective: http://www.hdtvprimer.com/ANTENNAS/merging.html
also
http://www.warrenelectronics.com/antennas/Jointennas.htm

If you could use a switch that would help.

About 100+ miles range: you are really pushing envelope, but if your city ordinance allow to erect really tall tower, you could install high-gain antenna for the direction, but targeting VHF atop of tall tower ....

AVS Forum has good thread for reading http://xxx.avsforum.com/avs-vb/showthread.php?t=381623

50' AGL like that ? http://xxx.avsforum.com/avs-vb/showpost.php?p=20543826&postcount=12080

[Davenlr]

That plot you posted is not helpful. Post the chart with the signal levels at your location for each of the stations.

[P Smith]

That plot you posted is not helpful. Post the chart with the signal levels at your location for each of the stations.

I just thought same thing - need full report with two more charts.

[SayWhat?]

I thought about using an ABC switch, but that would mean running three separate cables from the mast through the garage to the house, over 100' each including the run up the mast. And then there's the issue of the pre-amp.

Like I said, I can get the most distant stations at certain times from 35'AGL with a tree partially blocking. If I move the mast so it's clear of the tree and go up another 15', that should help a great deal. From there, at that height, there is little between here and there since I'm on a hill 40' above the surrounding area. It's almost a clear, unobstructed LOS for the most part.

I'll try to pull the rest of the chart up again later. I was hoping it wouldn't matter with the color coding for signal strength.

[Davenlr]

If you look at the NM(db) scale, if you have an antenna with at least 14db gain, and a preamp with less than 1.5db of noise, you should be able to pick up any station with a positive NM(DB) 80% of the time. Anything with a negative NM(DB) will rely solely on weather enhancement or luck. Anything listed as 2edge, basically requires weather enhancement to cause the signal to remain close to the earth, rather than shooting off into space or getting attenuated by ridges. Depending on the area of the country you live in, that enhancement could be a daily/nightly occurrence or rarely happen at all.

FWIW, There are two UHF and one VHF antenna that combined, work about the best in most roof mounted situations. A Televes DAT75 or a XG91 for UHF, and a Winegard 7-13 yagi for VHF hi. If you want that channel 5, you would be better off using a VHF LO/HI combiner prior to the vhf input of the preamp, and using a single channel 5 element antenna cut for channel 5 below the rotor.

If you add two antennas pointed different directions, and all the stations are far enough away as to not cause any multipath cancellation in the spitter/combiner, you can go that route, but will have approx 4db loss before the preamp on both antennas where they are combined.

[Jim5506]

Not having the numbers from your 2nd and 3rd DMA's, just looking at the length of the lines on the polar plot, it looks like DMA 2 and 3 are going to be very iffy, if not impossible.

Concentrate on getting as many channels as you can from the west (DMA #!), then put up another antenna to experiment with the 2nd and 3rd DMA's.

[SayWhat?]

I can get DMA 2 (pop. 100,000) pretty reliably with the antenna rotated that way, but then I lose everything to the west. DMA 3 is the one I have the most trouble with due to the distance, but it's also a more major city (pop. 500,000+), so I'd like to get them if possible. In DMA 1 to the west, there are about four smaller cities (pop. 50,000 or less) and the quality and bias of TV stations reflects that.




http://www.dbstalk.com/attachment.php?attachmentid=25766&stc=1&d=1307934538

[Davenlr]

Are you on top of the rift that runs east/west through Cape, or below it? Those signal strengths vs distance to transmitter are really skewed.

[SayWhat?]

E/O Cape by quite a bit.


I was just looking at this unit: http://www.cableandwireshop.com/3_star_4228_8-bay_multi-bow_hdtv_uhf_antenna.html

It's hinged so you can point the bays in different directions. There's also some discussion of using splitters in reverse to combine signals. I've heard different opinions on that -- some say you can do it, others say it's not a very good idea.

By 'skewed', are you meaning good or bad? I'm at about 375' AMSL and the 50' mast would put the antenna at roughly 425' AMSL. DMA2 is generally 380' AMSL or so and DMA3 is in the 500' range. There really isn't much in the way of obstructions in those two directions.

[Davenlr]

Yea, from the looks of it, it looked like you were down in a valley or something, with stations close by being listed as 2edge and down on the power scale. Obviously, if you are already getting two of the DMAs with that little 8 element (plus reflector) UHF section on a radio shack antenna, you might want to try that 4228 with the reflectors that pivot. I honestly had not seen that option on that antenna before. The original version was phased (two sides combined) with a phasing line, which eliminated any error from using a splitter backwards (actually that does work if done exactly the right way). If it will swing out enough to get your two primary DMAs, and the 4 bow-tie bays have enough gain to do it, it would be worth a try, especially at your elevation.

I would not put much stock in its ability to pick up VHF though, it is primarily a UHF antenna. If the DMA 3 is Nashville, I wouldnt waste to much time on it. At 105 miles and VHF, you will end up with noise dropouts, and unreliable signals most of the time. Evenings and mornings might be ok, but VHF skip from other channels will most likely cause terrible problems.

To combine two antennas using a splitter/combiner, you need a good quality one to start with, both antennas need to be pointed exactly the same direction, and placed 1 wavelength apart, use the same exact balun to convert 300 ohm to 75 ohm if required, and the two coax lines between the two antennas and the combiner have to be EXACTLY the same length. Even a small difference at UHF will cause phasing errors and could end up cancelling each other rather than combining. The best you can hope for if all is said and done right, is a 2.5DB gain after combiner loss doing it that way.

Id try that one you linked. If worst case, it doesnt work, put it in high gain mode, and it should well outperform your current antenna.

You can try combining two different type antennas with a splitter/combiner. Worst case, you will get cancellation of some channels, best case is you will get them all with about a 3db loss across the board from running them through the splitter/combiner. If you have 3db to spare, it might work. Use the new antenna for the DMA2 that is farther away, and point your current one at DMA1.

This is my antenna, and is good for TVFOOL levels down to -12DB (or about 70 miles on full power UHF stations):

[Davenlr]

Also, if you want channel 10 and channel 5 from Nashville, you could use Channel Master Join-Tenna combiners, hooked to two separate single channel antennas, one for channel 5 and one for channel 10. Those could be added to your main coax before it goes into the preamp. That would add those two channels to whatever you end up with for DMA1 and DMA2. It would also mean having 4 antennas on the roof :)

[P Smith]

I would look around your area if someone has four antennas pointing to all your desired directions sitting on tall tower, would talk to him about those stations and his antenna's farm.