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Engineer Don
11-15-2000, 11:53 AM
I know most of the world has switched to cable or satelite dishes, but I still use an antenna for my TV. I put in an attic antenna, and I can get a few stations well, but there are others I don't pick up well at all. I went to a site that maps your optimum antenna orientation in relation to the broadcast antennas, and it implied that if I aim the antenna in a given direction I can pick up a specific station (or cluster of them). The problem is I can aim the same antenna in two directions at once.

My question is what happens if I get another antenna and aim it at the odd broadcast antenna? Can I just splice the antenna wires together and get good reception on all the channels, or will the signals interfer with one another? Should I just break down and get a dish?

I hate the idea of spending $30 a month to get TV when I get all I can stand watching for a small investment. My wife, however, dislikes that we are missing one of the major networks, and is leaning towards a dish.

Shiva
11-15-2000, 12:05 PM
Go to Radio Shack and buy an antenna rotator. It's a motor/gearbox that mounts to the mast with a small control box that sits on your TV.

When you want to view stations to your south just turn the knob on the control box to "S". The antenna will rotate towards the south and you're good to go.

Arjuna34
11-15-2000, 12:23 PM
The rotator Shiva described is the classic solution to this problem, and used to be pretty common.

You can't just connect two antennas together- it will degrade the signals from both of them (it won't hurt anything though, it's just not optimal). Your best bet is to install both of them (ideally separated by 1/2 wavelength, or several feet, so they don't intefere with each other). Run two sets of wires(most likely 300 ohm twin-lead ("ladder line") to your TV, and use a switch box to switch between them.

Now that I think about it, you might try just connecting them together to see what happens. If the signals are pretty good, you'll probably be OK. The only problem is that each antenna needs to be matched with a 300 ohm load to provide optimal power transfer. By connecting another antenna to it, half of the power from one antenna will go to the other, and only half the power will get to your TV. If the signals are strong, it won't matter. You could also get some attenuation due to phase cancellation (where the signal from one antenna partially cancels out the same station being received on the other antenna), depending on the relative strengths of the received station on each antenna, and the exact antenna placement. You'll have to experiment!

Arjuna34

Engineer Don
11-15-2000, 12:24 PM
Thanks Shiva, but it won't work in my case. My antenna is in my attic, and the joists and beams don't allow for much movement. Putting the antenna in is like assembling a ship in a bottle. I could orient the antenna in just about any direction, but it's sort of a one time operation.

I am not allowed to mount the antenna on the exterior either.

Arjuna34
11-15-2000, 12:28 PM
If you're cramped for space, you could also try putting in an omnidirectional antenna, so you'd pick up stations from any direction. This reduces the antenna gain, so if the stations are weak this may not be acceptable. You could also try making a dipole antenna (basically just two wires- the classic rabbit ears, or an FM radio antenna), and seeing if you can adjust the wires to pick up all your stations with some compromise in quality. The two wires of the dipole don't have to be pointing in opposite directions, or even be straight.

Arjuna34

Shiva
11-15-2000, 12:30 PM
Ok, then. Can you put more than one antenna in the attic? I was going to suggest the basement, but...

Anyway, you could use more than one antenna if you only use one at a time.

You'll need some type of switching mechanisim though.

Crafter_Man
11-15-2000, 12:38 PM
Engineer Don:

I don't believe you can simply connect two antennas in parallel or series. For one thing, there would be a huge impedance mismatch. And who's to say the signals won't "subtract" instead of "add"? Suffice to say, connecting two or more antennas together would probably not work unless careful consideration was given to coax impedance, antenna impedance, max/min voltage points along the coax, stub lengths, and all the other garbage associated with distributive parameter systems.

Now Shiva suggested an antenna rotor. That would certainly be an acceptable solution, but it may not work if you have a large antenna in your attic. (I also have an antenna in my attic. It is rather large, and there's no way it would be able to spin 360 degrees.) Here are some other options you may want to consider:

1. Use an omni-directional antenna. The disadvantage, of course, is that these have low gain, and may produce "ghosting".
2. Install another antenna in your attic (pointed in a different direction than your present antenna) and switch between the two using a 2-to-1 coax switch.
3. Install the antenna outdoors (on a mast) and install a rotor. This, of course, is the best solution. But if you're like me, you don't want an ugly antenna sticking above your roof.

ZenBeam
11-15-2000, 01:05 PM
I am not allowed to mount the antenna on the exterior either.

Maybe, maybe not. If you live in a neighborhood with restrictions against outdoor antennas, the FCC has ruled those restrictions are illegal. (I don't have an online cite, I read this in the paper, and heard it confirmed at my neighborhood association meeting). If you live in a condominium, I don't know whether such a restriction would be invalid or not.

If you want to go the two-antenna route, you might be able to use a 2-1 splitter backwards. You'd have to get the two antennas both positioned so only one of them was picking up each station you wanted to watch. This would probably work if your stations are in only two directions (say from two different cities, both a distance away).

One last thought. If the stations you can't pick up simultaneously are all UHF, you could separate out the UHF part of a combined antenna, and attach only this part to a rotor. This would be much smaller, and probably could rotate in the space in your attic. Then you just need a UHF/VHF combiner (which they make).

astro
11-15-2000, 01:40 PM
Originally posted by Engineer Don
[B]I can aim the same antenna in two directions at once.

1: My question is what happens if I get another antenna and aim it at the odd broadcast antenna?

2: Can I just splice the antenna wires together and get good reception on all the channels, or will the signals interfer with one another?

3: Should I just break down and get a dish?
/B]

God...the memories of my mis-spent youth as a Radio Shack Manager who really liked antenna setups. A customer like you was a dream come true. Wires! Counter diagrams! Switches! Trips to the car with wire, rotors, antennas and switchboxes. Fat sales tickets! Gross profits!

Re question 2: Yes the signals will interfere. Potential for ghosting etc.

Re question 3 ... Yes just get the dish. Your life will be much easier and the picture will be worlds better though it's not nearly as much gearhead fun as a multiple antenna switching setup.

Chas.E
11-15-2000, 06:17 PM
Oh, how soon they forget. I can't believe someone actually said that you can't put multiple TV antennas together in one circuit. How ridiculous.

When I was young, and there was nothing but broadcast TV, my father had a fancy rig with 3 TV antennas on one mast. Each one pointed at a different TV station's transmitter. And we only had one TV.

In the distant past when Analog ruled, it was quite common to put several antennas together, especially in rural areas where you might have to point the antennas in different directions to pick up stations in different cities.

Now if you asked me how to DO it, I haven't a clue. And the design of fancy TV antenna rigs are becoming a lost art. I'm sure there are some experts around the net, you might fish around Usenet in areas like alt.radio* or alt.video*

casdave
11-16-2000, 01:38 PM
I would have thought that if there were problems in having areials spliced together because of impedance matching it would be possible to connect each one to a separate masthead amplifier and then connecting the outputs of those together.They would then be isolated from each other.

You might have some problems with cross channel interferance where the same signal is broadcast at two differant frequencies and they may interfere.

Another solution would be to get an omni-directional aerial with a mast-head booster.

Arjuna34
11-16-2000, 02:17 PM
Originally posted by casdave
I would have thought that if there were problems in having areials spliced together because of impedance matching it would be possible to connect each one to a separate masthead amplifier and then connecting the outputs of those together.They would then be isolated from each other.

You might have some problems with cross channel interferance where the same signal is broadcast at two differant frequencies and they may interfere.

Another solution would be to get an omni-directional aerial with a mast-head booster.

The problem with connecting two antennas together with amplifiers is that, while the antennas are now happy because each sees the proper impedance, the amplifiers are now seeing the wrong impedance- each expects a 300 ohm TV, not a 300 ohm TV in parallel with another 300 ohm amplifier.

Again, while not the optimal way to use two antennas, you won't HURT anything by trying it, and with the proper orientation (and luck), you might get good results. TV antenna impedances aren't well controlled in the field anyway (how many people use an impedance analyzer or spectrum analyer to tweak their antennas??), so it's not like it was perfect to begin with.

Cross-channel inteference should be no problem for the TV tuner to filter out, unless something wacky is happening.

Arjuna34

justwannano
11-16-2000, 07:06 PM
Use a splitter to connect the antennas. Keep the antennas as far apart as the longest element. You can buy individual antennas cut for a particular channel. The higher the channel number the smaller the antenna. Uhf antennas are much smaller than vhf antennas. I don't know about your area but around here one mfgr has designed a special antenna. It is in three pieces and is stacked. One is usually pointed NE, another N and the third SE. It is also possible to defeat the reflector element, the longest element which keeps unwanted signals from comimg in the back side, by cutting it shorter. I forget the measurement though.