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Stack 2 different UHF ant types/directions. Single mast Install and vert separation?s

post #1 of 5
Thread Starter 
I've been recruited to be a pair of hands on a roof install of two different style UHF antennas they already have and want to be stacked on a single mast for two different TVs. Sounds a bit odd to me so I thought I'd ask.

Any advice for the proposed single mast install of a Winegard HD4400 (vertical 4 bay UHF for a close transmitter) and a euro-Yagi-ish(?) Stellar Labs 30-2155 UHF facing 90 degrees from the first (for a more distant transmitter)? (I have put a up a 4400 before, but by itself.)

I'm not really getting the 1/2 to 1 longest wavelength separation stuff vs the collecting/capture area separation stuff I've googled. The lowest real channel of interest is 20 (~ 2ft wavelength(?)).

Thanks for any comment.
post #2 of 5
Quote:
Originally Posted by jam-h View Post

I've been recruited to be a pair of hands on a roof install of two different style UHF antennas they already have and want to be stacked on a single mast for two different TVs. Sounds a bit odd to me so I thought I'd ask.

Any advice for the proposed single mast install of a Winegard HD4400 (vertical 4 bay UHF for a close transmitter) and a euro-Yagi-ish(?) Stellar Labs 30-2155 UHF facing 90 degrees from the first (for a more distant transmitter)? (I have put a up a 4400 before, but by itself.)

I'm not really getting the 1/2 to 1 longest wavelength separation stuff vs the collecting/capture area separation stuff I've googled. The lowest real channel of interest is 20 (~ 2ft wavelength(?)).

Thanks for any comment.

I always use 7 to 10 ft vertical separation with good results. The idea is to not have one antenna interfering with the other. In the VHF days, it took more separation because the wavelengths are longer.
post #3 of 5
To get a full wavelength apart on UHF you will only need to be about 30 inches. Now I may not be completely correct here, but my assumption has always been that antenna spacing was only critical if you were pointing the two in the same direction for increase gain. I have used two antennas before, in separate directions, and had them quite close together, without problems. As a side note, I've used many of the Stellar Labs 30-2155's and love them. Especially the new design released earlier this year.
post #4 of 5
Quote:
Originally Posted by foxeng View Post

I always use 7 to 10 ft vertical separation with good results. The idea is to not have one antenna interfering with the other. In the VHF days, it took more separation because the wavelengths are longer.

But of course, foxeng always uses 400 foot towers with good results, too.

I have serviced over a hundred cut-to-channel off-air reception arrays, and I never could see any visual degradation between antennas mounted more than 1/4 wavelength apart on the same mast, though I have observed a beneficial front-to-back ratio developed by a channel 7 and an abandoned channel 9 antenna that was on the same mast, pointed in the same direction and inadvertently but fortuitously located 1/4 of channel 7's wavelength away. I had removed the channel 9 antenna to discard it, but saw that a ghost image had cropped up, and so I then reinstalled it and left it there where it functioned as as some kind of passive resonator, I guess.

My market had a channel 4 and 5 analog, as well as a 7 and 9, and typically, installers would put one lowband antenna and one highband antenna on the same mast, four to five feet apart and be good-to-go. The only time I ever incurred and had to remedy a "spacing" problem of sorts is when someone put the lowband antenna beneath the highband antenna and it was too close to the plane of the roof flashing.
Edited by AntAltMike - 8/3/13 at 8:05pm
post #5 of 5
Although I haven't run the two antenna scenario you describe, with UHF Yagi pointed 90-degrees from UHF 4-Bay, based on fol. Hi-VHF + UHF Stacked Antenna simulation results, I doubt that you will see ANY significant Raw Gain differences if they are closely stacked, but might see some reduction in F/B and F/R Ratios for the UHF 4-Bay. Try to get at least a few feet of separation between them:
http://imageevent.com/holl_ands/stacked/stackuhfhivhf
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