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Thread: Base Station Antenna sharing

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    Default Base Station Antenna sharing

    Looking for some input on my current project....

    I have a mid-power Astro Spectra VHF that I am going to be using as a base station here with a DB224 on top of a 35-foot tower. I think this will provide the coverage that I need, but I have very limited space on the tower for anything else.

    I'd like to also have a VHF antenna on the tower for a Uniden Homepatrol, but I don't want to damage the scanner's front end with the power from the Astro Spectra on VHF (or the other one on UHF for that matter). Is there a good way to couple the Homepatrol to the DB224 along with the Astro Spectra so that I can use that antenna for receive on both the scanner and Astro Spectra?

    Thanks!


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    YOu can use a duplexer to isolate the Astro spectras TX freq from the scanner. This will only work with a simplex TX freq if its trunked the answer is no. If you have to go to 2 antennas then there will be no way to avoid desense on the scanner when the astro spectra is transmitting. The fronend of the scanner should be able tohandle the "overload" but I recommend the largest spacing between the antennas as possible along with different hights.

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    The Astro Spectra's transmitter will burn out the poor scanner's frontend.

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    Yeah... I guess I will have to go with two antennas as the Astro Spectra will be used across a wide range of amateur and commercial frequencies. I was hoping to avoid that as I don't want to damage the scanner, but it looks like I will just have to take my chances.

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    The only thing somewhat similar to the setup you describe that could work is if you were operating the Astro Spectra on VHF and the scanner on UHF, 700/800, etc on a multiband antenna. You could use a diplexer like a Comet cf-4160 which would isolate the different bands from each other (I do this with one spectra on VHF and another spectra on UHF). But of course, since it looks like you want VHF capability on both the scanner and spectra on one antenna, that just can't be done in a frequency agile situation.

    Incidentally, they refer to items like the cf-4160 as "duplexers" but IMO, that's a poor choice of word since a repeater duplexer is a much different animal and typically when the term is used.

    As to the isolation between two separate antennas, like Notarola said, get as much vertical separation as you can. I definitely wouldn't expect any performance out of the scanner while the spectra is transmitting, but as to doing actual damage to the scanner's front end, that will depend on how much power you're using on the astro spectra and how much physical separation you've got between antennas.

    Here's a page which will give you an idea of isolation figures: http://www.repeater-builder.com/antenna/separation.html

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    I'd suggest modifying the AS to split the receive RF inside the radio and bring a sample out to another coax connector drilled thru the side of the housing. That way both the AS receiver and the scanner are disconnected from the antenna when you go to transmit.
    It is a fine thing to be honest, but it is also very important to be right