This is something I had never thought about but in light of the other post about radar I thought this maybe of interest to some.  The follow comments were offered by a pro game boat skipper on another forum.

"It all comes down to what you can afford at the end of the day and you get what you pay for, the bigger the array the better the quality.

The boat I run has a Furuno FAR2127 Radar, 25w with a 8ft array, frinkin awesome consistently get birds at 8nm and have had birds working at 12nm, some days if I had to choose I would take the radar over the sounder, its saved my bacon a few times.

The big trick I have been taught is to have the gain up very very high almost so the screen is coloured in then the birds will show up much better, some times they are just a faint blur/variation to the colour but if its constant it is more than likely birds. Hope this helps. Play with the gain to you get it sorted, even if you find a work up start playing with the radar so you know what it looks like in the future. The smaller cheaper radars still work, it comes down to playing with the gain, sure they may not find birds at 8 miles but 3 or 4 is better than missing it altogether and makes your covered area bigger in the day.

The radar is an important tool, the eye can only really see birds working at two miles so many a man would have been close and missed a work up / hook up only a couple of miles. If I would have to choose I would put more money into a radar than any of the other electronics on a fishing boat (Game fishing that is).

It’s a great feeling while steaming out to the grounds and spotting birds at 8 miles then heading straight to the action and starting the day in the right place.

Another trick I use on the radar is keeping an eye on other boats, if you and acquire a target on your radar you can see where they are fishing and even see if they are backing up on a fish."