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Berwick Amateur Radio Society
Susquehanna
Valley MESH Network
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Columbia Montour Amateur Radio Club

               
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Power amplifiers

You can add some oomph to your node by adding amplifiers. A low cost power amplifier can be attached in conjunction with a variety of gain antennas to greatly increase transmit power.  Bi-directional amplifiers could be used on both antenna connections.  A bi-directional works both ways, increasing both transmit and receive distance.

Use caution when doing this.  A hi gain antenna and a big power amplifier can cook things slowly if they are in the signal path.  The XYL may not be happy with piles of dead birds under your antenna...  You also don't want to hurt your neighbors.  At the very least you may disrupt all of the Wi-Fi in your immediate area if you bounce your signal around.  If you can't see a distant target directly, you probably shouldn't try to 'power thru the obstructions'.  It probably won't work, and it may not be safe to do so.  The following information was obtained from this link... http://hsmm-mesh.org/documentation/124-antennas-and-amps.html

Take note of the part where it is stated that a 25 watt bi-directional amp connected to a 24db gain dish will produce 6.2Kw EIRP

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Antennas and Amps
Written by Jim Kinter, K5KTF

We have had a number of people write regarding amps and antennas.

I sat and did some calculations ( http://www.csgnetwork.com/antennaecalc.html  ) .

With 79mW (stock) power from the node into a: 

3.5dBi (stock rubber duck) .176W EIRP
9dBi (yagi/omni/dish)  .62W EIRP
14dBi 1.9W EIRP
24dBi 19.8W EIRP

 

If you go with a 1/2W BDA (bi-directional amp--about $60-$80) into a:

3.5dBi (stock rubber duck) 1.1W EIRP
9dBi (yagi/omni/dish) 3.9W EIRP
14dBi 12.6W EIRP
24dBi 126W EIRP

 

And then, even a 2 watt BDA ($60-?00's ):

3.5dBi (stock rubber duck) 4.47W EIRP
9dBi (yagi/omni/dish) 15.8W EIRP
14dBi 50.24W EIRP
24dBi 502.4W EIRP

 

As you can see, no matter how many watts your pushing, having a better antenna ALWAYS helps out more than the amp, especially when you factor in cost.

I have seen a 25W BDA, for a couple thousand dollars, and drive that into a 3.5dBi Omni, your still only getting about 55W EIRP. (But that into a 24dBi dish will give you 6.2KW EIRP, enough to get fried pheasant/robin/bat/etc every night for dinner!-- If you cant hit your target with that, you must have too much dirt and concrete between sites.)

So your best bet will always be trying to connect with a good antenna first. If you connect, but its weak, THEN try an add a 100mW or a 1/2W BDA. Unless you like having dead birds on your property (already cooked!).

Dumping wattage into a weak antenna only propagates noise and makes things tougher for all

 

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