Question: Connect 2 Antennas, Maybe Join?
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Connect 2 Antennas, Maybe Join?


This is a discussion on Connect 2 Antennas, Maybe Join? within the DTV | HDTV Chat forums, part of the Over-the-Air (Antenna TV) category.


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  1. #1
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    Connect 2 Antennas, Maybe Join?

    If I connect my DB2 and EZ-HZ antenna with some type of 2 input and one output devise to my tv will I loose lots gain? I am not sure if this ? is properly asked.

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    billisnice,

    As a rule, it is not possible to connect two receiving antennas to one coaxial cable without causing large signal losses. The easiest way to do this is by using a common signal splitter, but that setup is a double-edged sword working against you.

    Picture the system as the letter Y where the upper legs are each antennas and the lower leg is the single coax. The three coax cables are connected with a common signal splitter. You might assume signals from antenna 'A' go thru the splitter to your TV set and signals from antenna 'B' also go to your TV set and this is partially true.

    The problem is as follows: signals from antenna 'A' also go to antenna 'B' and signals from antenna 'B' also go to antenna 'A'. From the start there is a 50% loss of signal strength, because half of the received signal (per antenna) goes to both the TV set and to the other antenna. Add to that the loss (usually about 3.5 dB) inside the splitter plus the loss from the coax.

    The rule has exceptions: (1) identical antennas pointing exactly the same direction can be combined using a common signal splitter. (2) VHF and a UHF antennas pointing in the same or any direction can be combined together using an inexpensive device called a UVSJ (UHF-VHF-Signal-Joiner) such as one from Radio Shack Part Number: 15-2586.

    So, to use two 'same-band' antennas requires two coaxial downleads and an A-B antenna switch to keep the antennas isolated from each other.

    Jim
    Jason Fritz and n2rj like this.

  3. #3
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    Quote Originally Posted by Jim In Seattle View Post
    billisnice,

    The rule has exceptions: (1) identical antennas pointing exactly the same direction can be combined using a common signal splitter. (2) VHF and a UHF antennas pointing in the same or any direction can be combined together using an inexpensive device called a UVSJ (UHF-VHF-Signal-Joiner) such as one from Radio Shack Part Number: 15-2586.
    Bill,

    You can use the UVSJ to get the VHF off the EZ-HD or RCA ANT751 (or other Hi-VHF antenna) and combine it with the UHF off the DB2.

    Dan

  4. #4
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    Dan, where can you get the UVSJ? Do you have much signal loss using it...thanks

  5. #5
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    Solid Signal, Summit Source and other places online have it.

    The insertion loss is minimal, somewhere on the order of 0.5dB.
    Ryan, N2RJ

    Extra class certified antenna NUT

  6. #6
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    Quote Originally Posted by Jim In Seattle View Post
    billisnice,

    As a rule, it is not possible to connect two receiving antennas to one coaxial cable without causing large signal losses. The easiest way to do this is by using a common signal splitter, but that setup is a double-edged sword working against you.

    Picture the system as the letter Y where the upper legs are each antennas and the lower leg is the single coax. The three coax cables are connected with a common signal splitter. You might assume signals from antenna 'A' go thru the splitter to your TV set and signals from antenna 'B' also go to your TV set and this is partially true.

    The problem is as follows: signals from antenna 'A' also go to antenna 'B' and signals from antenna 'B' also go to antenna 'A'. From the start there is a 50% loss of signal strength, because half of the received signal (per antenna) goes to both the TV set and to the other antenna. Add to that the loss (usually about 3.5 dB) inside the splitter plus the loss from the coax.

    The rule has exceptions: (1) identical antennas pointing exactly the same direction can be combined using a common signal splitter. (2) VHF and a UHF antennas pointing in the same or any direction can be combined together using an inexpensive device called a UVSJ (UHF-VHF-Signal-Joiner) such as one from Radio Shack Part Number: 15-2586.

    So, to use two 'same-band' antennas requires two coaxial downleads and an A-B antenna switch to keep the antennas isolated from each other.

    Jim
    The other problem is that you're likely to introduce multipath from such a setup if the antennas are pointing in different directions.
    Ryan, N2RJ

    Extra class certified antenna NUT

  7. #7
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    ki4hpz

  8. #8
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    UVSJ is on the way..i may not need one, but having another option in the attic is a good thing...

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    Quote Originally Posted by billisnice View Post
    Dan, where can you get the UVSJ? Do you have much signal loss using it...thanks
    Billisnice, et al:

    For readers who may want one a bit faster than by mail-order I wrote this in my answer, above:

    "...using an inexpensive device called a UVSJ (UHF-VHF-Signal-Joiner) such as one from Radio Shack Part Number: 15-2586"

  10. #10
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    Ok, did not know radio shack have them.

    When I get the UVSJ in my hands go downstairs and find my rabbit ears from long ago and connect them using my UVSJ to my DB2 and forget buying another antenna. All I really need is a few Hvhs stations. Is that ok? Here is my tvfool stuff again at TV Fool

  11. #11
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    FYI I called Radio Shack where I live and they have them in stock for $15 each, and I order one on line with shipping for $4.74 w/o tax.

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    Quote Originally Posted by billisnice View Post
    FYI I called Radio Shack where I live and they have them in stock for $15 each, and I order one on line with shipping for $4.74 w/o tax.
    Ouch! I think I paid about $8.00 the last time I bought one at the Shack. Who says there isn't any inflation?

    I tried your TVFOOL link above, but it doesn't work for me.

    Jim

  13. #13
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    I agree. The Skywalker SKY26701 VHF-UHF Separator-Joiner is still available for about $2.89 if you want an alternative to the Radio Shack product. Now that I think about it, this may be the same product that Radio Shack is selling.
    n2rj likes this.

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    Quote Originally Posted by billisnice View Post
    Ok, did not know radio shack have them.

    When I get the UVSJ in my hands go downstairs and find my rabbit ears from long ago and connect them using my UVSJ to my DB2 and forget buying another antenna. All I really need is a few Hvhs stations. Is that ok? Here is my tvfool stuff again at TV Fool
    Channels 8 and 10 are good and strong, so in theory combining the rabbit ears and the DB2 should work. Let us know how it works out, and if you have any more problems.

  15. #15
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    Curious, would a db4...i think is two db2 one on top of another make much of a difference with UHF gain?

  16. #16
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    Yes it has more gain and the vertical beamwidth is narrower. I have a 16 bay which is composed of two 8 bays vertically stacked. 2.5dB more gain and it makes a significant difference in my situation.
    Fringe Reception likes this.
    Ryan, N2RJ

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  17. #17
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    Quote Originally Posted by billisnice View Post
    Curious, would a db4...i think is two db2 one on top of another make much of a difference with UHF gain?
    In theory if you connect two antennas that are pointed in different directions you lose 3.5 dBs of gain, but if you point them at the same stations you gain 3.5 dBs. So, a DB4, which is twice the size of a DB2, will have 3.5 dBs of gain more than a DB2 (and a DB8 has a theoretical 3.5 dBs gain over a dB4). Given the strength of your stations I doubt you would need it, unless you really want to pull in channels from further down the chart.

  18. #18
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    Actually you only gain 2.5 not 3.5. The .5 db is insertion loss of the combiner which is the same for both scenarios.
    Ryan, N2RJ

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  19. #19
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    Quote Originally Posted by n2rj View Post
    Actually you only gain 2.5 not 3.5. The .5 db is insertion loss of the combiner which is the same for both scenarios.
    Wouldn't that make it 3 dBs of gain then?

  20. #20
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    Quote Originally Posted by dkreichen1968 View Post
    Wouldn't that make it 3 dBs of gain then?
    Only if there was no insertion loss in the splitter/combiner device which isn't the case. The insertion loss is a constant 0.5dB loss so you take a 0.5dB hit if you either gain or lose. So for same direction it's 2.5dB and for different directions it's -3.5dB. Without combiner losses you gain or lose 3dB which is roughly twice or half the power respectively.
    Ryan, N2RJ

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