# combining two ota antennas



## gregftlaud (Jun 16, 2004)

is there a piece of equipment i can use to combine two directional uhf/vhf antennas into one line and be able to get the best of both signals?

one antenna gets certain channels really good and others not so or at all.......the same for the other. i just want to combine them so i can get the best from each.

i've seen uhf and vhf combiners but that isnt what i'm looking for. also a simple splitter doesnt work all signal strengths come in very low.

thanks
greg


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## rlj5242 (Dec 20, 2000)

The jointenna. Go to the parent forum (AVS) and search in the HDTV Hardware section for "jointenna". There are dozens of threads about them.

-Robert


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## newsposter (Aug 18, 2002)

jointenna

http://www.warrenelectronics.com/antennas/Jointennas.htm

this thread or a google should help you out

http://www.avsforum.com/avs-vb/showthread.php?t=381623


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## gregftlaud (Jun 16, 2004)

na jointenna isnt what i'm looking for. i need something that accepts all frequencies and takes the best of both signal strengths for each channel and gives me that one. the jointenna only has models for either uhf or vhf separately and not both all in one.


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## newsposter (Aug 18, 2002)

i definitely would be interested in such a device as well!


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## texasbrit (Mar 17, 2004)

gregftlaud said:


> na jointenna isnt what i'm looking for. i need something that accepts all frequencies and takes the best of both signal strengths for each channel and gives me that one. the jointenna only has models for either uhf or vhf separately and not both all in one.


No, sorry - no such device. The problem is that for any one station, the signals arrive at slightly different times through the two antennas, so combining them causes all sorts of problems (like multipath, one of the biggest problems for digital reception). Antennas also pick up stations through the back of the antenna, creating more opportunities for multipath. In the worst case you can end up with no receivable signal at all, in most cases some of the stations have better signal and some worse. You can try to use a standard splitter/combiner and see what happens, but for most people the results are disappointing. Occasionally the stations and signal strengths just happen to be OK to combine but it's not usually the case. That's why people with stations in different directions use rotors.


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## TyroneShoes (Sep 6, 2004)

gregftlaud said:


> ...i need something that accepts all frequencies and takes the best of both signal strengths for each channel and gives me that one...


That would be a dream device indeed.

The closest thing would be a pair of rare and hard-to-find filters from a MATV equipment supplier like Blonder-Tongue, but that would end up costing you around $300 and would not really be all that effective. These devices have a number (3-4) of notch filters for lowering the level of unwanted carriers, and are designed to even out reception levels prior to amplification for a MATV distribution system. They are primarily for NTSC reception but might work to some extent for ATSC, I guess. To be really effective you would probably need a couple of hi-pass or lo-pass filters to maximize the effectiveness, so add a couple hundred $ more to your project (Microwave Filter Inc. is the best source for those). These companies rarely sell to the public. And these guys frown on returns if it doesn't work out the way you expect.

The reason combining antennae at the same frequency doesn't usually work very well for ATSC is because directionality is the best tool against multipath interference, and when you combine two directional antennae together you effectively turn them into a single less-directional antenna. If you're in even a mildly-reflective environment, that usually turns out to be an exercise in frustration.

The best thing to do is look at the various receive sites and decide which channels you can sacrifice permanently from both. If you can narrow it down to just a few, you might be able to use a jointenna or a uhf/vhf combiner. Another idea is to just bend over and accept the HR20 for the big 4 in MPEG4 (I never said it was a "good" idea), and design a simpler antenna system for CW, MyTV (lots of HD movies coming up from the FOX vault), and PBS OTA. Otherwise, sad to say, you're probably SOL.


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## A J Ricaud (Jun 25, 2002)

gregftlaud also a simple splitter doesnt work all signal strengths come in very low.
thanks
greg[/QUOTE said:


> How about amplifying the output of the splitter? If the signals are just low but not noisy it may work for you.


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## rminsk (Jun 4, 2002)

A J Ricaud said:


> How about amplifying the output of the splitter? If the signals are just low but not noisy it may work for you.


You would have severe multipath issues.


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## A J Ricaud (Jun 25, 2002)

rminsk said:


> You would have severe multipath issues.


Maybe, maybe not, especially if the amp has an adjustable output. Probably have to fool with the aiming of the antennae, too.


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## captain_video (Mar 1, 2002)

You'd definitely have multipath issues with VHF antennas if you try to combine them. UHF antennas tend to be highly directional and are better suited for what you're asking. I have two Channel Master 4228 UHF antennas joined with a standard VHF/UHF splitter/combiner and there are no noticeable multipath problems with the outputs. Both antennas are pointed in the exact opposite directions so the chances of multipath interference are greatly reduced. 

If you're trying to receive OTA HD channels using this setup and the channels are all on UHF then you might want to try a similar configuration. If only one or two channels are in VHF then you can use a VHF only antenna in a fixed position and combine the output with the UHF antennas. If you have both UHF and VHF channels in one direction and additional UHF channels in another direction then you might be able to combine a VHF/UHF antenna with a separate directional UHF antenna. The only way to know for sure is to try it and see.


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## newsposter (Aug 18, 2002)

TyroneShoes said:


> That would be a dream device indeed.
> 
> .


I had thought that but not well informed enough to make a blanket statement. But I'm still interested in such a device lol.

someone could make a lotta money if they could figure it out


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## henryld (Aug 16, 2005)

I remember seeing, some time back, a few articles about screening or shielding antennas to make them highly directional and less susceptible to multipath. IIRC it involved building a box frame with conductive screen attached on all but the front side. Don't remember how well it worked but it might be something worth researching.


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## aVOLanche (Jul 20, 2004)

Google "stacking UHF antennas".It's complicated.I have 2 antennas pointed in different directions and joined with a simple 2-way splitter.For some channels one or the other works best.For other channels,both antennas together work best.I had to do a lot of experimentation to position them.


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## Jerry_K (Feb 7, 2002)

I have two antennae combined with a simple two way splitter working backwards and a four output Radio Shack amplifier. Works great. I get both Baltimore and Washington DC channels on one input.


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## TyroneShoes (Sep 6, 2004)

captain_video said:


> ...I have two Channel Master 4228 UHF antennas joined with a standard VHF/UHF splitter/combiner and there are no noticeable multipath problems with the outputs. Both antennas are pointed in the exact opposite directions so the chances of multipath interference are greatly reduced.
> 
> If you're trying to receive OTA HD channels using this setup and the channels are all on UHF then you might want to try a similar configuration. If only one or two channels are in VHF then you can use a VHF only antenna in a fixed position and combine the output with the UHF antennas. If you have both UHF and VHF channels in one direction and additional UHF channels in another direction then you might be able to combine a VHF/UHF antenna with a separate directional UHF antenna...


While stacking two directional antennas to receive the same single signal with increased diretionality can be done professionally (I think I cashed a check or two for that) and combining a U and a V to get signals from various directions usually works OK if you engineer it properly, your setup is quite interesting, and I am not at all surprised at its effectiveness. It sounds, though, like you are using one antenna for U and the other for V, which brings up the question why not use antennae that are more targeted to U and V rather than antennae that are each capable of both? That should actually be a more-workable strategy and provide success in more setups of that nature.

Also, maybe not in your case if you have a particular channel with a particular multipath angle, but in most cases like this you should be able to get the same or even better results with a single yagi that doesn't have a good front-to-back ratio, and point it to the weaker stations. This allows the stronger stations to be received by the back lobe, which is typically nearly as strong as the front lobe, while otherwise maintaining good directionality.

One of the things that makes the 4228 the antenna it is is that it has a high FTB ratio. Combining two of them and pointing them in opposite directions destroys that, but in certain cases that's OK, such as yours. Also, the U/V combiner minimizes that. To make your particular setup even more effective, I have a suggestion: For the 4228 on the UHF side, separate and isolate its two screen halves using some sort of non-conductive tape, and for the V side, bond its two screen halves together with some heavy-gauge chunks of electrical wire. That will make each more selective for U or V, respectively, and make them even less-susceptible to off-angle interference.



> You'd definitely have multipath issues with VHF antennas if you try to combine them. UHF antennas tend to be highly directional...


Not as a rule. Higher frequencies are more directional so multipath may in some cases have a tendency to get worse at lower frequencies, but UHF antennae are not more directional, generally speaking. There is nothing definite about multipath other than that. Each location is unique.


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## TyroneShoes (Sep 6, 2004)

henryld said:


> I remember seeing, some time back, a few articles about screening or shielding antennas to make them highly directional and less susceptible to multipath. IIRC it involved building a box frame with conductive screen attached on all but the front side. Don't remember how well it worked but it might be something worth researching.


That would be similar to a Faraday cage. Most transmitter buildings are lined with sheet copper or copper mesh to trick the local high RF to ground. I think the only practical application for an antenna is if there is a single high-level carrier on a different frequency that is overloading the antenna, which is very different from a multipath issue.

The problem with doing it on an antenna is that the minute you add more structure near the antenna, that tends to destroy the natural directionality the antenna already has. It is also difficult or impractical to do. This is also exactly why if you do have multiple antennae they should be separated by at least a wavelength, the further the better, preferably on separate masts, and why they should be away from other structure, possibly on standoffs. A good example of this phenomena is how UHF reception can vary on an indoor antenna just by someone walking accross the room. This is also why the tuning technique for rooftop antennae is adjust-step away-adjust-step away. Otherwise, reception tuning can change the minute there is no longer a human body next to the antenna mast.

Stacking antennae to increase directionality for a single frequency is based on a very similar phenomena. They are typically positioned using precisely trimmed-to-length cabling and spaced in 2 or 4-antenna arrays exactly 1/4 or 1/2 wavelength apart, which allows the received signals to combine in phase. When you place two antennae close together in different directions to get lots of channels, the same phenomena can cause the signals to combine out of phase for some frequencies, effectively destroying overall gain and directionality.


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## A J Ricaud (Jun 25, 2002)

TyroneShoes said:


> Stacking antennae to increase directionality for a single frequency is based on a very similar phenomena. They are typically positioned using precisely trimmed-to-length cabling and spaced in 2 or 4-antenna arrays exactly 1/4 or 1/2 wavelength apart, which allows the received signals to combine in phase. When you place two antennae close together in different directions to get lots of channels, the same phenomena can cause the signals to combine out of phase for some frequencies, effectively destroying overall gain and directionality.


I was hoping you would chime in on this. I recall reading about stacking antennas for more gain 30-40 yrs. ago but could not recall the spacing requirements.


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## aaronwt (Jan 31, 2002)

gregftlaud said:


> is there a piece of equipment i can use to combine two directional uhf/vhf antennas into one line and be able to get the best of both signals?
> 
> one antenna gets certain channels really good and others not so or at all.......the same for the other. i just want to combine them so i can get the best from each.
> 
> ...


I have two Squareshooters which are directional setup this way. I have a problem getting one station and the antenna needs to be pointed an inch or two to the side, but when I do the other station signals drop some. So I combine two of the squareshooters and don't have any problems. They go to the combiner then go to the preamp and then to my condo.


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## henryld (Aug 16, 2005)

TyroneShoes said:


> That would be similar to a Faraday cage. Most transmitter buildings are lined with sheet copper or copper mesh to trick the local high RF to ground. I think the only practical application for an antenna is if there is a single high-level carrier on a different frequency that is overloading the antenna, which is very different from a multipath issue.
> 
> The problem with doing it on an antenna is that the minute you add more structure near the antenna, that tends to destroy the natural directionality the antenna already has. It is also difficult or impractical to do. This is also exactly why if you do have multiple antennae they should be separated by at least a wavelength, the further the better, preferably on separate masts, and why they should be away from other structure, possibly on standoffs. A good example of this phenomena is how UHF reception can vary on an indoor antenna just by someone walking accross the room. This is also why the tuning technique for rooftop antennae is adjust-step away-adjust-step away. Otherwise, reception tuning can change the minute there is no longer a human body next to the antenna mast.
> 
> Stacking antennae to increase directionality for a single frequency is based on a very similar phenomena. They are typically positioned using precisely trimmed-to-length cabling and spaced in 2 or 4-antenna arrays exactly 1/4 or 1/2 wavelength apart, which allows the received signals to combine in phase. When you place two antennae close together in different directions to get lots of channels, the same phenomena can cause the signals to combine out of phase for some frequencies, effectively destroying overall gain and directionality.


From what you are saying it would probably be a real PITA even if it did work to some degree. No telling what it might look like to boot. Wish I could remember where I saw that article(s).


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