Somewhat disappointing DFF1 performance (NOT ANYMORE)


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I have a NavNet 3D system ( 3 x MFD12, 1 x MFD 8 displays, DRS6A radar, DFF1 with an Airmar SS270W transducer, GP330B receiver, HUB101, FA-30 AIS receiver and Airmar PB200 weather station ). On the whole, I am very happy with it and would highly recommend it. :furuno

The one aspect that left me a bit disappointed was the sounder performance, for such a top notch sounder/transducer combination. When the water gets over 100m deep, it still shows the bottom on the screen, but not the depth reading. Beyond about 250m, it loses bottom altogether, even if I slow down to a crawl. All I see are a few thin vertical lines on the split screen ( I normally use a split HF/LF screen ). I had the range on manual with range set for 1000m. I tried both the manual setting (with gain from 50% to 100% ) and the Cruising setting, to no avail.

The transducer was well installed by a competent custom boat builder and does not appear to be in line with anything capable of generating turbulence (and the fact that the problem persists at very low speeds probably rules turbulence out, anyway). The transducer uses the Airmar high speed fairing. The boat is a 46 ft power catamaran with twin inboard diesels.

Any ideas on what might be the problem or suggestions for improvement? :?
Would reducing the Picture Advance Speed help?
Appreciate any inputs.
Thank you for your question. In 3D there is a separate control for the sounders digital readout, you will find this control under the SYSTEM MENU then DFF1/3. The control you are looking for is called BOTTOM LEVEL HL & LF. I think the default setting is 0 but reset them both for -20 to -25. This should help in shallower waters. The DFF1 needs to have a digital readout for the Auto Range/Cruising/Fishing modes to work properly. While I have never tested the DFF1 with SS270 to see how deep they will go I would think 600-700m is about their limit depending to water conditions.

Only now have I been able to get back into deep enough water to check. I have set Bottom Level HL & LF to -21, but I still lose the digital depth readout at depths greater than 150 meters.
This happens even at trolling speed, so turbulence is not a factor. I tried both HF and LF - same thing. The actual view of the bottom, though, looks good and clear even at 230 meter depths ( the deepest water that I was able to reach , this time). Only the depth reading disappeared. :questions

Is there any other adjustment that I should try? :sorry
Try setting the both the LF/HF BOTTOM LEVEL settings more negative.

Thank you, Snips, will try. A couple of questions will help me understand what I am doing:
- How negative do you think I should go?
- What does the Bottom Level Setting do?
The Bottom Level control sets a threshold for the what the sounder considers a valid bottom. The more negative the number the more sensitive the sounder becomes. However if you go to far (negative), the sounder can became to sensitive. An indication of this would be if you drove over a dense school of fish and the digital readout jumped from the bottom to the fish school.

Thank you, Snips, it makes sense. I will set it for -27 at first. Next time I am in deep water, will try gradually higher negative values until it I get a reading at 230 meters, but no further.
This weekend I conducted a thorough review of the sounder set up and found out that the dealer had inverted the LF and HF when setting the sounder through the installation Wizard. Changing to how they should originally have been set made a lot of difference to the general performance of the sounder. :jump

I also set Bottom Level to -27. With both changes, I never lost digital reading for the bottom when trolling even at 240m depth. However, I did find that, when going thru deep water at planning speed (25 kts), the digital reading was jumping around a bit, as you had prdicted that it might. I set Bottom Level back to -21 and the jumping around stopped. I suspect that the inversion LF/HF was the root cause of the digital reading disappearing at depths greater than 150m (Snips, does that make sense to you? ). But since, by then, I was at 130m depth, I cannot be sure that the problem is gone... it will take another fishing trip.
Good for you finding that the frequencies were reversed. I am 99% sure that was the main source of the problem. You probably found also that after you switched the frequencies you needed a lot less gain to see fish. It would be interesting to reset the BOTTOM LEVEL settings back to zero and recheck to see how well the sounder holds the digital readout.


Sorry for only updating this now, but I don't get to go into deep enough water except in our Nov-Jan bluewater fishing season.
I fine-tuned Botton Level in deep waters and the sweet spot seems to be -15, for both LF and HF. LF gives, perhaps not surprisingly, the best view of the bottom by far, in waters deeper than 130 meters or so.
Thank you for your help. The sounder is working very well, now. :furuno
But, of course, any additional improvement tips will be appreciated...
The Bottom Level setting really only helps the Digital readout/Auto Range function, it doesn't affect fish targets. If you can post a screen shot along with the settings you are using I will look them over to see if changes could be make.


I finally made it back to really deep water (600 m - 720 m). At that depth, I could not get a digital readout and no real image (other than clutter) on the screen. After fiddling a lot with the controls that I think I understand :think , the best results came with the settings below. I will try to post a picture in the very next post. This allowed me to just see the bottom and at least try to find an elevation of about 120m that should be there, but no detail at all.
Here were my settings:
Trolling speed (8 its)
LF (the HF screen was blank)
Picture advance : ½
Clutter 67%
TVG 5 or 6
Bottom level LF : +13 (anything lower and the digital readout appeared, but showing a much lower depth

Any suggestions?
You are approaching the depth limits of the DFF1/SS270W combination. Changing the TVG settings will only affect the gain in the upper portion of the water column. Other than making sure your output power is set at 10 there is not much more I can suggest. I would like to see a screen shot when you have one.

sorry to dig up an old post snips but do your comments re BOTTOM LEVEL CONTROL apply to my NN3D/MFD12/DFF1/B260 apply?

my setup rarely displays the depth when in deep water. it will display 400 to 500m on a calm day on the drift, but not on the move.

in deep water on the troll it just displays ___._m

Bottom Level is the threshold setting for seabed detection. If you find that the BL setting is at 0 try -20.