Thread: Fishfinders, Dual beam and dual frequency ?.

Whats the difference between dual beam and dual frequency in sounders ?.
I'm looking at a Garmin Fishfinder 140 for estuary use but they are only made in dual beam. The 140 has 2 frequencies and 2 cone angles as do most dual frequency sounders so I'm a bit confused.

Cheers,
Anthony.

I have a Humminbird 737 with quad beam trsnsducer. The transducer looks the same as a normal one. It is dual frequency with the normal straight down beam plus side beams which extend on a 45 degree angle each side. This is where the quad beam comes from - 2 x side beams plus 2 x frequencies with standard beam. With the side beams turned on I can see as far out the side of the boat as I can see deep, but this is restricted to waters less than 25m deep. So if I am in 10m of water, I can also see 10m each side of the boat. Handy for spotting lumps and drop offs that aren't in your direct line of travel. The dual frequency is mainly used for different depths. I can't remember off the top of my head which one is better for shallow or deep, but one gives a narrower beam than the other (IIRC). Narrower beam is better for deeper water as it gives a better picture of what is directly under the boat, and also returns stronger readings in this scenario. My last sounder was a Garmin FF140 (pre dual frequency) and it used to do a pretty good job of things in shallower water. I found at the time that it had the highest pixel count of sounders in that class, so it gives a better picture. IMO it was the best value for money sounder in its class at the time of purchase.