Will 2 antennas conflict for DTV?

[Drummerboy]

Instead of purchasing a rotor I wasing wondering if it was possible to have two UHF roof antennas connected at the same time but pointed in opposite directions (one pointed to Madison and one to Milwaukee)?  Will they cause interference with each other?  I am trying to avoid getting a rotor if possible.

[bradsmainsite]

Typically NO, but however there are exceptions.  If you happen to be exactly
in the middle with exactly equal gains from both directions maybe. :confused:

Here comes the problem even if that is your case.

You can have a great signal from the antenna pointing in one direction, but
remember off the back side of the other antenna you have a bad signal.
Now your going to take and mix together a bad signal with a good signal!

What will you get probably a bad signal.

In the case of digital signals not much expirimention has been done with that
however I would expect pixaltization to occur quite frequently, but one never knows till you try it! :confused:

You might want to save yourself the fustration and money and get the rotor, or
run too cables and use an AB switch, but make sure your antennas are at least
one wave length apart on the lowest channels frequency that you will use!

Good Luck!

Brad

[wxndave]

I would advise no about hooking 2 antennas together.  The problem that you will  probably have is called multipath.  As the signal bounces off of other buildings in you area the reflection could cancel the main signal causing a lower signal reading.    In analog this would produce a ghost image.  With digital it would cause high bit errors which could cause break up.   There is nothing wrong with trying it.  Just understand that it could be a problem.  The only other way you could do it is to filter out the rf channels for Milwaukee from the Madison antenna for example.  This could get expensive.

Years ago there was an antenna made for the Rac/Ken area that would work for Milw/Chi.  This antenna was mounted on the same boom and had a large relfector in the middle of the boom.  Last I heard they didn't work well for digital.

[Gregg Lengling]

I'd like to chime in as many new integrated tv's have dual antenna inputs.  You could run 2 feedlines and feed each antenna to a different port and teach your set which channel uses which antenna.  Of course this depends on the set you are using and whether it has this option.

[audiopile]

Twin antenna idea keeps surfacing - I've yet to run into anyone who has gotten this to work at all well. The only post I've ever encountered  that claimed great results was someone who went from a indoor antenna to some sort of twin outdoor antenna setup. Given that outdoor antennas will always blow away indoor - this wasn't a big surprise.
     I think that there is a tendency to confuse the new ( DTV) and the old (RF). In terms of antennas we are dealing with a RF signal - very old hat and very mature technology. While I have been really impressed with the number of antenna  products with HD stamped on the box - the truth is that nothing has really changed in terms of picking up the RF signal. At least locally - it's hard to beat a Channel Master 4228 installed as high as possible outdoors on a rotor and wired with at least RG-6 ( 6QS even better). This has a disgustingly high probablity of working really well. Not very exotic, not very expensive - just works.

[mhz40]

I agree, combining them is looking for a disaster.  Go with Greg's idea using two RF inputs on your TV (or an RF switch).
Antenna spacing should also be considered.  A rule of thumb is that they should be vertically separated by at least the length of the longest element of the largest antenna.  (Largest being element length, not boom length.)  Good luck!

MHz40

[Matt Heebner]

I have two antenna's installed in my attic. One is RS double bow tie, and the other is a RS UHF rooftop type. I use a regular RS combiner for the coax. I have the big UHF pointed to the Capitol Dr. antenna farm, and my double bow tie aimed due east to pick up FOX's digital signal. Granted it is not rooftop mounted but all my signals strength jumped about 4-5 points, and FOX now comes in rock solid at about 80%. Most all are 93-99%.




If you look close you can see the big UHF, and kinda see the double bow tie to the front and below the UHF. (it actually was hanging from  one of the elements, but it kept slipping off )

Anyways...works for me.

Matt

[tazman]

Just to chime in here once myself.  I had brought this topic up once last year.  At that time I was looking for a remote selectable AB switch, one that could be tower mounted near the antenna's.  The only ones I could come up with were ones for HAM radio use that were rated at 1000 watts and they cost 2 to 3 hundred dollars.  It would be ideal to be able to switch between antenna on the tower or roof and only have to deal with one feed cable.  Gregg since since your a CQ'er, you must have a little more exposure to these things than the average guy.  Are there any products other than the ones I found that are less expensive and are suitable for 75 ohm use? :wave:

 Otherwise combining 2 antenna together that are pointed in different dirrections would have an adverse effect on gain, unless you were to use RF traps designed to filter or pass only certain frequencies, and those are also expensive.  WineGard I believe has a white paper on the subject, as well as Channel Master.

[audiopile]

I thought chanel 6 was ( while disgustingly low powered) - finally moved down to the antenna farm off of Cap dr.?  While cheerfully willing to admit that  results count - I can't figure out why this set up works? Matt have you tried either antenna by itself ?  in my efforts to get  6 a while back - I ended up buying a Sencore DTV signal strength meter . Every dual antenna on a single cable set up I tried ended up measuring and working worse than either antenna by itself. By spacing my antennas as far apart as was pratical ( I rent - so it's a attic mount) - I was able to wire them up to the two seperate inputs on a Hughes E-86 box - in other words seperate cables untill it hit the STB. This works for me and has the important advantage of getting reasonable analog picture quality on 10/36 for those times I can't stay up for three hours to watch in SD-DTV.
     I have tried dual antenna hook ups at a few customer's homes and it didn't work for any of them either ? Spacing antennas is truly a issue in itself. Like so many others - i have simply come to depend on CM 4228's high and outside for customers installs - it just plain works.
     Again - results rule - if it works for you - go for it.

[Matt Heebner]

That's the funny thing. I CAN NOT get all the digital channels and FOX with one antenna. I can either get all the digital's and not FOX, or I can get FOX, but lose half of the digitals. Trust me, this is after hours of trying to get both. The only way I can pick up FOX is to aim my double bow tie east. Any more north and I think WISN over-powers FOX.

Why does this work for me......I have no idea. I set this up with me in the attic and  my son infront of the STB with it's signal meter both with walkie-talkies. I hooked up both and right away my son indicated a jump in signal percentage. I then started aiming to receive both local digital's and FOX with maximum strength.

I've spent more time in my attic trying to get FOX and the rest of the digital's than I care to think about...but I get 'em all, and like I stated previously all in the high 80-90 signal mark.

Matt

[bradsmainsite]

Whats happening here is that when you shift the antenna to get fox 6  you are
also attenuating the amount of signal from the adjacent channels excessive
signals and are probably finding ch 6's hot spot.

Once fox 6 catches up to everyone else this should resolve your problem.

For now you are in the same boat as the rest of us. :bang: