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How can I use two OTA antennas?

Discussion in 'Digital Over the Air Television Talk By RabbitEars' started by cr0mag, Nov 28, 2004.

  1. cr0mag

    cr0mag Thread Starter Active SatelliteGuys Member

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    I have an attic mounted antenna, and I receive all of my OTA signals fine except for Fox. I live so close to the towers that I almost need two antennas pointed in different directions. Is there a way to set up two antennas and combine the signal onto one lead going to my reciever?
    If it matters, I'm looking mostly for the digital signals. Really don't care about the anaolg stuff.
    Thanks.
     
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  2. al

    al Supporting Founder Supporting Founder

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    You can buy a combiner specifically to combine two antennas, the problem is multipath. I would first try to aim your antenna towards the Fox station, and see if you can pull the others off the back of your antenna. You could also try a preamp on your antenna as well.

    Alan
     
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  3. cr0mag

    cr0mag Thread Starter Active SatelliteGuys Member

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    Thanks alan, I'll try the amp first, as my attic is very restrictive and I can't "turn" the antenna at all. The dropout on fox only happens once in a while, so I'm hoping the amp is all that I need.
     
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  4. Hutch001b

    Hutch001b Member

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    I bought an electronic remote A/B switch at Radio Shack and it worked fine. Only problem was having to deal with another remote. Hutch
     
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  5. vsvier

    vsvier New Member

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    My current set-up uses three OTA ant., I have 2 yagi style UHF (there signals are combined on 1 line using a splitter) and 1, 4 bay bowtie style VHF ant. I than ran the single line from the splitter into the UHF side of a channel master combiner, and than ran the Bowtie to the VHF side of the combiner. the single line out from the combiner than goes to one leg of a diplexor (the other leg is the signal from the sat.) than a single line is run to the recv. where another diplexor splits the OTA, and sat signals for input to the reciever. this setup eliminated the need for a rotator, also note that I have no pre-AMP (my signal at the ant is in the 90's, my signal at my 811 is in the 80's). just for reference, I live in central CT, and I now get all the OTA channels I want :)

    Before plugging in a pre-amp, here is some info that may be helpfull to you.
    I think a lot of people misunderstand what a pre-amp does. All a pre-amp does, is compensate for loss of signal over the cable run, It does NOT increase the signal gathering capibility of your antennea. For example if you were to hook up a signal meter, or monitor and tuner in your attic as close as possible to the antenea, and adjust the ant. for max signal (lets say you get 80%), and than you were to make all your connections, and than hook up your signal meter, or monitor /tuner in the viewing area, You MAY see a lower signal. this is caused by many things, for example: you can expect a 3 db loss for a solid 100' cable run, an additional 3.5 db loss for each splitter or diplexor in the line, and an additional 1 db loss for couplers. as you can see the numbers COULD add up quickly, or they could be negligable (no splitters, short runs). So, lets assume you have 2 diplexors, and 100' cable for a total of 10 db loss, and your signal in the viewing area is now, lets say 75%, the best you could do would be to place a pre-amp (something around a 10 db gain) in the system to get you back to the 80% you had right at the antennea. By putting in a 23 db gain pre-amp (CM7777), you are now "overdriving " the signal, causing noise, which translates to a signal loss for a digital signal. The increased gain would not get you any higher than the original 80% you had in the attic. The only thing you can do to increase that number is to try a different ant., or adjust its pointing. Bottom line, A Pre-Amp does NOT increase the signal gathering capabilty of your ant.

    hope this info is helpful, good luck
     
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  6. Carl B

    Carl B Supporting Founder Supporting Founder

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    To crOmag:

    Joining the signal from 2 antennas is no big deal, but the results are not predictable. I've turned experimenting with different antennas, pre-amps, CM JoinTennas, and combinations in my attic over the past year into a hobby.

    Using an inexpensive RadioShack splitter/combiner hybrid (~$4) is just fine for combining the output signal from 2 antennas. Now there are all sorts of rules-of-thumb that say it's better to use 2 identical antennas, it's better to have the leads from both antennas to the combiner exactly the same length, and it's better not to involve pre-amps in the multiple antenna equation. However, I can tell you that you can follow all the rules and fail and not follow any and succeed. You just need to have a plan and implement it. Check the results. If not satisfactory, modify the plan and try something else.

    Depending on the azimuth angle between the 2 DTV signal sources you are trying to receive and the radiation patterns of the antennas, the results may exhibit severe multi-path or you might get lucky as I have in some setups and just hit a null point in the radiation pattern and no multi-path.

    For your particular problem I recommend the following. Go to this site and obtain the magnetic azimuths from your house for the 2 DTV signal source locations.
    http://www.antennaweb.org/aw/Welcome.aspx
    Point your attic antenna at the azimuth for the several DTV channels. Confirm your signal strength. In small increments, rotate your antenna toward the azimuth of the Fox channel. Stop when you start losing adequate signal strength on the several channels. Get Fox yet?

    No? Leave the antenna pointing in the last direction tried and try a pre-amp. RS has a great return policy. Buy one (~$45), try it and return it. If it gets you everything and Fox, go buy a good ChannelMaster Titan 2 on line for about $55. Problem solved.

    No? Re-aim your current attic antenna at the multiple channel azimuth. Install your 2nd antenna and aim it at Fox. Combine the downleads w/ the RS hybrid combiner. Check you locking and signal strength on all the DTV channels. Problems?

    Yes? Probably multipath. Buy a ChannelMaster JoinTenna for the Channel # of your Fox station from Warren Electronics on-line about $25. Install it on the downlead from the antenna pointed at Fox per the included directions for passing the set channel, before the hybrid combiner. That should take care of any multi-path problems.

    About pre-amps, as you will see at sites like Warren Electronics and Stark Electronics, particularly if your antenna isn't mounted outside on a high mast, a good, low-noise pre-amp will make your antenna function like a much larger antenna. You will also note on the Antennaweb site in the description of antenna color codes and commensurate antennas that certain conditions require a pre-amp for reception. This side of it has nothing to do with your cable length. However, if you also have a 100 foot or more coax run (make it quad shielded RG-6 by the way), you may also need an amplifier to boost the captured signal sufficiently to have adequate signal at your TV.

    Good luck and let us know what you do and how it works out.
     
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  7. Kevinw

    Kevinw Proud Staff Member Pub Member / Supporter

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    Great How to , Carl
    Thanks
     
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