Antennas and Amps PDF Print E-mail
Written by Jim Kinter, K5KTF   

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

I sat and did some calculations (  ) .

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.