Yagi antenna for monitoring P25 trunked system

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Ubbe

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This is a perfect situation to use cheap RG6 coax from a yagi and then in the attic, or wherever the coax enters your roof, you put a low-noise amplifier. That will give you more signal than any costly high grade coax cable can do. You probably need to attenuate the signal 6-10dB down at the scanner to avoid getting into overload issues with too high signal levels Most amplifiers powers from a USB connector so you probably have a mains outlet in the attic where you can connect a 5volt USB adapter.


/Ubbe
 

mmckenna

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The building is a Television production facility, so lightning protection, and fire suppression isn't that much of an issue. We have several things in place to stop that. We have cable troughs that route cable throughout the entire building. Moving everything from video and audio to data and now RF.

OK, as long as you are aware of the requirements, my job is done.

I found a 100ft chunk of LMR-400 on eBay with an N connector on one end, and a BNC on the other.

LMR-400 is good. However, you don't want to connect it directly to your scanner. The cable is pretty stiff and the strain on the antenna connector on the back of the radio will be high. It's not uncommon to snap off antenna jacks. It's usually industry practice to use a short whip of more flexible cable to make the final connection to your radio. That removes the strain and saves the connector.


Should be fine. Personally I'm not a big fan of Tram/Browning products, as I find their quality is lacking. There are some good lower cost antennas sold for the cellular booster market. Not much worse quality, but quite a bit cheaper.
 

Cowley639

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Ubbe

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You see those 4 tiny elements at the front of the antenna, those are for the 2GHz band and you more or less have only one element for the 800Mhz band. So it works almost like a single dipole at 800MHz with no gain and no directivity, it's almost an omni reception from all directions at 800MHz.

/Ubbe
 

Cowley639

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So just an update to everyone; I have a buddy who has a subscriber radio (handheld) on the state system, he came by my office with his radio and it was receiving all the talkgroups I am wanting to listen to. It did have a few drop outs, but again it was a handheld with a "short" antenna on it in my office in the middle of the building with no windows.

So I would think a Yagi outside pointed at the tower site with some LMR-400 would work just fine. Thoughts?
 

Cowley639

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LMR-400 is good. However, you don't want to connect it directly to your scanner. The cable is pretty stiff and the strain on the antenna connector on the back of the radio will be high. It's not uncommon to snap off antenna jacks. It's usually industry practice to use a short whip of more flexible cable to make the final connection to your radio. That removes the strain and saves the connector.
What do you suggest as a good jumper from the LMR into the Scanner?

RG-58?
 

skideric

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I'm using a Homemade,built like a Tank DTV Antenna with 4 "Bowties" & reflector with holes opposite the Bowties.Picks up P25 in next counties over from me.Prob 25 ft high,but i do still have trees.Of course the Local P25 System almost BLOWS me out...LOL !

EDIT: Also using a Brand New RS Discone Scanner Antenna,had found year or so ago at a thrift store...about same height.
 
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mmckenna

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So I would think a Yagi outside pointed at the tower site with some LMR-400 would work just fine. Thoughts?

It should.

The reason his radio was working is because the receivers and filtering in those radios is much better than what you'll have on a scanner. Adding the Yagi and good coax should solve your reception issues.
 

scanmanmi

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Does a Yagi need to be tuned to the specific tower site control frequency?
No. I was ready to throw my radio out due to simulcast and then I picked up a 900 MHZ 15 element ham yagi at a hamfest and now it's great. I can pick up 60 miles but I'm kind of elevated here. Yes I said 15 element. (RG6 by the way)
 

scanmanmi

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If you cannot pick it up now, then the issue might be what's called "topographical shielding", or in simple terms "too much dirt between you and the transmitter". Over 20 miles, you need to consider antenna height at each end and make sure the curvature of the earth doesn't get in the way.

Go to Google Earth, click Add then Path. Click your location and then the transmitter location and hit OK. Right Click the path (the mouse will not change) and click View Elevation Profile.
If you want to adjust antenna height right click the path and go to properties, altitude.
 

Cowley639

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Thanks for all the responses everyone!

I ordered some stuff today, Ill let everyone know how it works once it arrives.
 
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