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Old 02-11-2009, 01:57 PM   #1 (permalink)
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Default Combining Two TV Antennas

Combining Two TV Antennas

By combining two TV antennas together, you are able to receive TV stations in two different directions without needing the use of an antenna rotator. This kind of installation can be done successfully, but proper spacing must be kept between the two antennas to help prevent the antennas from interfering with each other and causing ghosting on the TV picture.

The formula for determining the minimum vertical spacing between the two antenna booms is a half l (wave) of the lowest channel to be received. To calculate this distance take 467 and divide it by the lowest TV channel frequency that will be received by either of the two antennas. So for example, if the lowest channel received by either of the two antennas is channel 2, you would take 467 and divide it by the lower frequency of channel 2 (54 MHz). This would give you the minimum vertical spacing of 8.64 feet or 103.7 inches that would be needed between the two antenna booms.

If two antennas will be spaced apart horizontally (such as in an attic) it is recommended that they be separated by 1 wavelength instead of a half wavelength as in vertical spacing.

There must also be the exact same length of coaxial cable between the two antennas and the combiner, which is basically a backwards two-way signal splitter. The same exact length of coax cable between each of the two antennas and the combiner is needed also to help prevent ghosting from occuring on the TV's connected to the antenna system.

Even if you properly separate the two antenna together and have equal lengths of coaxial cable you can run into problems. The biggest problem is when one of the two antennas starts to receive the station(s) in the opposite direction (from the rear) that it is pointed. This can create ghosting on all of the TV's connected. To reduce or eliminate this problem in residential antenna systems, bandpass filters and channel traps are used.

JOIN-TENNA

An inexpensive bandpass filter/channel trap is the Channel Master JOIN-TENNA coupler. The JOIN-TENNA coupler has two 75 Ohm coax cable inputs and one 75 Ohm coax cable output. One of the two inputs is connected to a bandpass filter that lets only the single specified channel through. The other input is connected to a channel trap to filter out the single channel while passing all other channels. By only letting the single channel through one input and trapping it out of the other input, the amount of interference is reduced.

The JOIN-TENNA coupler model is selected by the single channel that you wish to combine with all of the other channels. The JOIN-TENNA coupler cannot be used to combine adjacent channels, except for channels 4 and 5, and channels 6 and 7. The JOIN-TENNA coupler can also be used as a -20dB single channel trap. Be sure not to trap channels ajacent to the ones that you desire.
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File Type: jpg jointenna1.jpg (7.7 KB, 139 views)
File Type: jpg jointenna2.jpg (8.8 KB, 121 views)
File Type: jpg jointenna3.jpg (9.3 KB, 120 views)
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Old 07-17-2009, 12:44 AM   #2 (permalink)
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Default Combining 2 UHF bowties

Hi.

Being on the Niagara peninsula, I am in a location where the Toronto DT stations are almost 180 degrees away from the Buffalo DT stations. It has been suggested to me by a local dealer that I can mount two CM4228s back to back on the mast.

Having read your post above, since these antennas are both backed by reflectors, will the suggested installation be OK? I imagine the ghosting you speak of is more applicable to analogue, no?

Thanks.
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Old 07-19-2009, 01:49 PM   #3 (permalink)
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I would aim at Toronto and depending how far you are from Niagara I wouldnt even point in that direction as you wil receive the signals off the side and back of the antenna. if you choose a second antenna possibly aim it at another location taht is semi close to you to receive other channels... you may be able to get Erie Pansilvania... so with that set up you will get T.O Buffalo and Erie... best thing is get as high as you can without physical obstructions like buildings and trees...even hills and try different directions to see what you will receive...

I reccomend this on a cooler nigh since on warm days over 25 degrees C you will receive many more stations that you normally would not receive.
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Old 07-21-2009, 05:14 PM   #4 (permalink)
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Can ota antenna combines with cable-tv signals using this method?
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Old 07-22-2009, 07:53 AM   #5 (permalink)
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Quote:
Originally Posted by ateichman View Post
Hi.

Being on the Niagara peninsula, I am in a location where the Toronto DT stations are almost 180 degrees away from the Buffalo DT stations. It has been suggested to me by a local dealer that I can mount two CM4228s back to back on the mast.

Having read your post above, since these antennas are both backed by reflectors, will the suggested installation be OK? I imagine the ghosting you speak of is more applicable to analogue, no?

Thanks.
On any TV antenna there is a front to back ratio, the FB on two antennas will combine and cause problems, to put two bowtie antennas together back to back you must put a separator between them, and this should be several layers of aluminum window screen grounded to an earth ground with a 10 gauge aluminum wire.
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Old 07-22-2009, 07:54 AM   #6 (permalink)
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Can ota antenna combines with cable-tv signals using this method?
No, use an A/B switch, you dont ever want to connect a TV antenna to a cable feed, even with a splitter.
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Old 07-22-2009, 02:13 PM   #7 (permalink)
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Default More on the separator screen

I get the FB ratio point.

Both the CM4228s are backed by a reflector grid. You are suggesting this in addition to those? If so, can the screen be connected to the back of the grids, or does it need to stand free in order to be effective or not make things worse? I think you can see where I am going here - mounting two antennas back to back on a mast leaves about 6 inches of room between them, filled with mounting hardware and mast, so there is not a lot of room, although placing the screen on the grid would be easy.

Down the street, one of my neighbours has an antenna side-mounted off a tower with a piece of mast that is bolted to the tower, then veers off at 45 degrees, then goes vertical again long to hold the antenna. This means their CM4228 stands about 12 to 14 inches off the side of the tower. Would using something similar to add another foot of space between my two antennas help? Would it be best to simply slide one down the mast so they are not totally back to back?

I'm trying to come up with the most effective solution for a very limited space. Right now, my results are pretty good, but there is still one station that is on the verge of coherence (CTV) that I would like to get clearly. All others are in pretty good shape.

Thanks in advance, and I greatly appreciate the assistance that this forum provides.
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Old 07-26-2009, 06:04 PM   #8 (permalink)
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Sorry I didn’t get back to you on this,

The proper way is to make a frame for the screen, (painted wood) then mount the antenna to it, you want isolation from the other antenna the only common point would be the ground, and the screen should be grounded at one point only. Also the screen should be bigger by 3” all around then the antennas back grid.
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Old 07-26-2009, 07:06 PM   #9 (permalink)
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Default Much obliged...

Thanks for the assistance - I certainly didn't expect you to be sitting waiting for my next email.

I have a piece of expanded metal mesh that would be large enough to do the trick. The benefit is that it would be self-supporting and not require the wooden frame. I think I may try that first, since it is just collecting dust in the corner of the garage right now. When I try either antenna alone, I get no discernible reception off the back side since I'm in the fringe for both broadcast centres.
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Old 07-26-2009, 09:48 PM   #10 (permalink)
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Originally Posted by ateichman View Post
I get the FB ratio point.

Both the CM4228s are backed by a reflector grid. You are suggesting this in addition to those? If so, can the screen be connected to the back of the grids, or does it need to stand free in order to be effective or not make things worse? I think you can see where I am going here - mounting two antennas back to back on a mast leaves about 6 inches of room between them, filled with mounting hardware and mast, so there is not a lot of room, although placing the screen on the grid would be easy.

Down the street, one of my neighbours has an antenna side-mounted off a tower with a piece of mast that is bolted to the tower, then veers off at 45 degrees, then goes vertical again long to hold the antenna. This means their CM4228 stands about 12 to 14 inches off the side of the tower. Would using something similar to add another foot of space between my two antennas help? Would it be best to simply slide one down the mast so they are not totally back to back?

I'm trying to come up with the most effective solution for a very limited space. Right now, my results are pretty good, but there is still one station that is on the verge of coherence (CTV) that I would like to get clearly. All others are in pretty good shape.

Thanks in advance, and I greatly appreciate the assistance that this forum provides.
where are you located(city) that you are having difficulty receiving CTV ?
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