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Indoor VHF Antenna

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70cutlass442

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I am adding a VHF receiver to our high school for the police radio system. My original plan called for a Larid fiberglass antenna on the roof bu have some concerns that I will lose some sensitivity directly under the antenna inside the school. Would I be better off installing a RX antenna inside the school someone, say in the middle? Is there a good antenna to use? My current idea would be to take a ceiling tile and place a metal plate in it as a ground plane and use a Phantom or some other low profile antenna.

Has anyone done something similar that can offer some input?
 

mmckenna

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Not sure I understand.
Are you adding a voting receiver setup to assist with repeater coverage?

Location will depend on where your coverage deficiencies are. If indoor coverage is the issue, then an antenna indoors might help.
 

Ubbe

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If you use a non gain antenna it will have coverage under it and usually radiosignals will bounce around anyway and find it's way up to the roof. If you have a metal roof on the building then you probably have to make other arrangements. It all depends of the size and structure of the school and needs one guy with a radio connected to the antenna you plan to use and at that location and another guy running around doing radio tests. It should be done using a free adjacent frequency or TG.

In large buildings like a hospital with 4-5 different floors and a basement below ground level I used antennas, GP type that doesn't require external groundplane, at the center of each floor connected to a receiver and a RX voting system.

/Ubbe
 

N4DES

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The maximum amount of gain is on the horizontal plane, so if there is something adjacent to the building you can put the antenna on the better.
When I deployed a small downtown trunked system, that has a primary use is to provide in-building coverage in our 14+ story County Courthouse and nearby State Attorney/Public Defender building, I put it across the street on a top of an adjacent building.
 

Ubbe

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If you are allowed to put up an antenna at adjacent buildings you could use a high gain directional antenna pointing at the school.
But it all depends of how large the school building are. It's anyhow often most convenient and economical to install an antenna inside the same building.

/Ubbe
 

cmdrwill

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And Fred KNOWS what he is talking about.

So, we NEED more complete information on the existing system.
 

WB9YBM

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Just a side-note regarding fiberglass: I've seen deterioration caused by UV. The most common solution I've heard about is after cleaning it using metal-free paint for protection...
 

Ubbe

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Radiating coax are extremly expensive and you have to treat it as an antenna, using plastic standoffs to keep it at least 5 inches off any metal and the total cost incl installation are huge. You only see that being used in tunnels and locations under ground and anywhere where walls cannot be penetrated with RF signals.

Most buildings can use a single antenna to cover one floor. Installing the radio in a room next to the antenna will spare the cost for extended lenghts of expensive quality coax.

/Ubbe
 
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