FF frequencies in sonar and down (scan) imaging

[AbuMasgouf]

When I bought my FF last year I never spent anytime learning the differences in the frequency of the signals for either the sonar or the down (scan) imaging. My FF (587ci HD DI Combo) has the following:
Down Imaging®
Sonar Coverage

455 kHz / 75° @ -10db
800 kHz / 45° @ -10db

DualBeam Plus™
Sonar Coverage

200 kHz / 28° @ -10db
455 kHz / 16° @ -10db


Depth: 350ft (DI)/600 ft.

I have three questions,
1) What is the main difference between the different frequencies and what does it really mean to me?
2) What should I keep the settings on most of the time?
3) How wide of an area do I see under my kayak, thus does it matter if my transducer is in the Bow or the Stern of my kayak?

I did a search online but a lot of the information gave me mixed signals, so I figured I'd ask more experienced folks and be able to follow-up with them for clarification. Thanks in advance for the edification

[sparky1423]

Wish I could help Bro...with my FF, the less I know the better! I have to admit the next FF I purchase will not have the DI, I actually prefer the sonar unless there is a lot of chatter and inference on the screen. Hopefully Yak Fish will chime in, he has a similar model and is pretty handy with the features.

Have you had a chance to use the chip?

[AbuMasgouf]

Have you had a chance to use the chip?

Not on the water. I tested it by navigating the map and finding bodies of water and the details are really nice. I can't wait to see it in action on the water. the Feb M&G will be the first attempt!

[ES Fisherman]

The best thing to do is take some time to mess with the settings next time you are on the water and marking fish/structure. I don't have down imaging but have found that when shooting through the hull (both in my kayak and skiff) the lower frequencies tend to give better returns. You want the transducer to be placed in an area where it will receive the least amount of interference, so the lower the better.

[HearadonCatch]

As far as what you should run for a setup, that would be determined on where you fish, and what your looking for. Best option is to play with the settings, but don't change too much when your first messing with it.

For how wide of as area, that depends on the finder. Typically user manuals give you a good idea of that coverage.

[Turtle135]

The main difference between the frequencies is the size of the sonar cone.



I'm a freshwater bass fisherman. I am usually using the narrow 16 degree cone (the 455kHz frequency) traditional sonar. I am not looking to mark fish. I am looking for subtle changes in the bottom (like creek channel edges, cover items, etc.) that tend to hold bass. With my fisher finder more narrowly focused I am able to pickup those changes in the bottom.

When I mess around with the down imaging I am usually just trying to see how good of an image I can get of a cover item down below. I have had down imaging for a couple of seasons now and for practical fishing purposes I really do not use it.

[daolai]

Abu - good post as I was looking for the same information - Dave - good picture and can you convert the freq to a diameter in terms of feet?

[khobombed]

What it boils down to is the higher the frequency the shallower the range, but you get a more reliable reading and less false hits. If you plan to fish on top of less than 200 ft of water under you the 200 KhZ is a good start. If you get a lot of clutter you want to switch to higher frequency to make sure you are getting solid hits, but your depth range will decrease. As Dave illustrated, the cone angles decrease in width in the higher frequencies. There is a lot more info here: http://www.lowrance.cn/Support/Tips-...onar-Tutorial/

[AbuMasgouf]

Thanks for the info gents. Especially for the picture Dave, I totally missed that from Humminbird.

So with that understanding. If I'm in 15+ FOW it wouldn't matter if the transducer is installed in the bow or stern of my kayak. The angles would cover the whole area underneath. Is my understanding correct?

[Turtle135]

see below, just dealing with traditional sonar (leaving down imaging out for the moment), the diameter of the circle on the bottom would be the "coverage" of your sonar signal



1. with a 16 degree cone

depth: 5 feet, diameter of the circle: 1.39 feet
depth: 10 feet, diameter of the circle: 2.78 feet
depth: 15 feet, diameter of the circle: 4.17 feet
depth: 25 feet, diameter of the circle: 6.96 feet
depth: 50 feet, diameter of the circle: 13.92 feet
depth: 75 feet, diameter of the circle: 20.87 feet

2. with a 25 degree cone

depth: 5 feet, diameter of the circle: 2.16 feet
depth: 10 feet, diameter of the circle: 4.33 feet
depth: 15 feet, diameter of the circle: 6.49 feet
depth: 25 feet, diameter of the circle: 10.82 feet
depth: 50 feet, diameter of the circle: 21.64 feet
depth: 75 feet, diameter of the circle: 32.47 feet

You can use those as rough numbers to get an idea of how much bottom coverage your sonar signal is picking up.

However....

Humminbird draws these nice neat pictures of sonar coverage based on those "perfectly shaped cones". In reality, out on the water, the sonar cones are not quite so perfect (but we could start a whole new thread just on that topic, so I will leave it alone for now).

[AbuMasgouf]

Thanks Dave I really appreciate the info. This will also be a good resource for others

[Turtle135]

I just edited that post, check it again, I had made an elementary school math mistake!

[AbuMasgouf]

I just edited that post, check it again, I had made an elementary school math mistake!

No worries bro! You've been really helpful

[PigPen]

Thanks for the info. I just got a 4-dsi for Christmas and only need a batter TT and a fuse before February's meet and greet. I'll be using an over the side mount from RAM if it ever gets here.

[daolai]

Dave - great information very helpful