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Thread: Extending In-Building VHF Coverage- Ideas?

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    Default Extending In-Building VHF Coverage- Ideas?

    So I have a building I'm trying to improve VHF coverage in. The building is a typical government-issue metal portable building, few windows.

    I'd like to do this passively, otherwise I'm going to have to source another mobile.

    Ideas?
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    I am assuming that you have portable users inside this structure? Is it a talk out, talk back problem or both? Is a repeater used or simplex? How critical are the communications? Are multiple channels involved?

    Passive solutions are usually ineffective because there is additional free space loss added from whatever antenna reradiates inside the building to the portables. If the building is in fact an effective faraday shield and there is ample signal outside it may work. But it is rare to have such favorable conditions. Especially if the building is rather large inside.

    If you have a decent VHF yagi to use as a donor antenna, you can attach some low loss cable between it and a whip antenna inside and give it a try.







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    Yes, this is for portable users that prefer a radio on their desk when they're in the office. Comms aren't life safety critical but are critical to the mission itself.

    We have two pairs we use, both Quantars (one analog, one P25), with excellent coverage outside the structure. The structure itself is small, about 30' x 60', and completely open inside (no additional metal walls).

    I'll get my hands on a yagi and do some experimentation and see what happens.
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    Another option would be to look into a BDA/DAS type setup. It'll be a little more then the above mentioned but may work out better for you.
    "Scanner hobbyists have conjured up the idea that a new, unscannable technology is not interoperable"

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    I would go the BDA route with radiax down the core of the building.

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    BDA's for VHF are going to require duplexer filtering so be prepared for a cost that will be silly for a few desk bound folks.

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    I would think a pair of single pass cavities should be enough. Many shops have a few spare cans laying around. Since this is only a 30x60 area he may ba able to work with a good yagi to a 1/4 interior antenna using good cable (heliax) in a passive configuration. If that is not satisfactory he can add in the amps.

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    Quote Originally Posted by Notarola View Post
    I would think a pair of single pass cavities should be enough. Many shops have a few spare cans laying around. Since this is only a 30x60 area he may ba able to work with a good yagi to a 1/4 interior antenna using good cable (heliax) in a passive configuration. If that is not satisfactory he can add in the amps.
    Assuming his problem is only in one direction, with an amplifier, that would be a workable fix.

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    Apologies for the delayed reply. Thanks for the ideas so far!

    The problem is bi-directional, but the building is not a perfect Faraday cage. Sometimes the portables can hit the repeater, and sometimes there's enough signal strength inside to actually hear a call while inside. But not all of the time.

    I'm trying to improve service to the point where there is some reliability.

    Given the budget (aka, my wallet),a BDA type setup will be out of the question, unless I can find one at a price point that's worth experimenting with.
    When in danger,
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    Scream and shout.

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    Try the passive (outside)yagi/omni(inside) configuration first this may work well enough as the building is small enough. Use good cable. If that fails then you will have the antennas ready for trying some type of BDA or amplified configuration.

    I think between RFI and myself we may be able to find something that will work and fit your budget.

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    With two yagi's, two whip antennas, two TX lines, two VHF bandpass filters and two low noise RF amps with moderate gain, one could build a poor man's junk box BDA. You would need the BP filters to be on the input of the RF amps and the antenna isolation and gain set very carefully to avoid feedback and uplink noise. God forbid this mashup does not oscillate!

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    A 30 x 60 portable metal building means a double-wide trailer with steel or aluminum siding.

    Perfect coverage outside, and sometimes able to tx/rx with a portable inside means outdoor RSSI is close to the bottom of performance (-100 or less), with just enough isolation to drop rssi down another 10-20db to the point of failure.

    Add in portable uplink rssi, and we have asymetrical system performance.

    Add in this is the VHF band subject to noise from ethernet and most modern electronics, and we have a compromised downlink field adjacent to the portables.

    A real single channel VHF BDA would probably exceed the cost of the building, add an unneccassary level of complexity, and more likely be a FUBAR generator than an aid.

    Passive repeaters made from back to back antennas are radio unicorns. People imagine them, but reality never strikes. If you want to go the passive route, cut several VHF quarter wavelength slots in the metal siding with a circular saw all around the building until the indoor RSSI becomes acceptable. Or have large windows installed on all sides.

    The real solution is a base with tone remotes spread around the office. Well understood technology.
    You can add a PA to fill the room with sound.
    You can use a NXU attached to the base with PC-NXU at each computer so the remote control is on every desktop.

    Following this line, you can add voting receivers at the building to increase the uplink performance, and simply use the base to provide receive audio to the room.
    Bow wow wow yippie yo yippie yay

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    How MANY users? On how many different frequencies? Do they have to be able to transmit, or just receive?

    It might be more cost effective to set up an audio network to speakers on the desks from a couple of receivers.

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    As Bill suggested,

    JPS NXU / NXU-PC is probably your most cost effective solution, but you might also look at Telex IP-224 / IP-2002 handset instead of PC software.

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    Thanks to all for the input! Here's the update, and solution.

    I finally had time to explore this issue again. By explore, I mean walk around the portable building speaking into one radio and listening to my P25'd voice from other radios placed around the room. Moving myself and the other radios, I made two discoveries:

    First discovery. The offending radio seems to be in the one place of the building that is a dead spot. Could possibly be EMI, as the same desk has four monitors, two laptops, and a plotter next to it. Guess who's that one is?

    Second discovery. I was unnecessarily ageist when considering the problem and assumed that newer meant better. I have no test equipment to confirm this, but it seems that the well-taken-care-of APX is slightly deafer than the rest of the "fleet", comprising of mud filled XTS5000s that get used as field-expedient hammers and fly smashers. The APX seems like it takes a second longer to unsquelch and was always the first one to drop the repeater signal.

    Solution: Move the offending radio six feet to the right to solve the immediate problem. I probably need to have the APX aligned as well.

    Thanks again to y'all for the ideas.
    When in danger,
    When in doubt,
    Run in circles,
    Scream and shout.

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    Who would have thought that older radios work better than a pricey new APX toy?

    Here is my recommended universal Motorola APX , BaoFengShui tune up tool:

    https://www.tigertoolsupply.com/ABC2...-p/abc20bf.htm

    It is OSHA and FM approved brass and fiberglass.

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