Re: I Need A New Marine Radio and Antenna...What's Best?
OK lets see if I can explain this to it's easy to understand.
db or Decibel of gain, is the appearance of signal gain with an antenna. An antenna of 8db of gain appears to collect and transmit the signal better than a antenna with 2db of gain.
Logic here would say then always go with the biggest db you can get. Like most things in life it's not that easy.
Think of the signal coming out of your antenna as a large doughnut. With a 2db gain antenna the the doughnut that the antenna sends out is large and round. so it covers a large area up and down, but not out.
Now take that doughnut and smash it flat. It's now thin and spread out. This would be a 8db gain antenna. The beam goes out further, but in a more focused pattern.
This is important and the trade off are important here because your antenna will always send the signal out perpendicular to the mast(antenna). So as your boat pitches and rolls the "doughnut" is moving with the antenna. If you have a high gain antenna the signal if very focused and won't always find the other radio.
Think of it like a flashlight shining at a specific rock on the bank, this rock we'll imagine for a second is the other radio your trying to talk to. When the beam is very focused(high gain like 8db+) it harder to get the light on that one spot, but it projects very far. Now take that same light and make it a flood beam (like a 2db antenna), it's now much easier to light up that same object, but the beam may not go as far because it's spread out. Same concept.
Very high gain antennas are normally used on base stations because they don't move around. Mid gain like 4-6db normally on power boats. The antenna moves around, but normally not huge, so the higher gain here is still useful. low gain (0-2db) are normally used on sail boats because the antennas are usually mounted way up high on the mast, and the movements of the boat are greatly amplified way up on top of the mast.
Hope this helps. I've been doing this stuff for years so I get it, but to someone that doesn't play with it all day long it can become very confusing very quick.
Bill