TVG Setting for FCV 1150

[42Duffy]

Great sounder. Wish the manual was a lot more detailed.

Trying to understand the TVG settings for the FCV 1150. The unit is connecter to a R209 Xducer running at 45 on the low and 170 on the high.

The TVG menu has a depth setting, a numerical setting, and a graph. I'm looking for a detailed explanation of what these settings actually do. TVG adjusts gain to compensate for signal loss due to the combined affect of spreading loss and absorption loss. Spreading loss increases by the square of the distance, the inverse-square law. Absorption loss increases with distance. Does the TVG depth setting compensate for signal loss only within that selected range and ignore targets beyond that range? Most of my fishing is tuna fishing in 300 feet or less. Therefore I'm promarily concerned with individual tuna fish and midwater bait. My experience has been if I set the TVG depth at 300 feet (or the water depth I'm fishing), 1 or 2 on the numerical setting, and low or zero gain I gett too many echoes close to the bottom. I get better results with a TVG depth setting at 2 to 3 times the actual water depth, 2 or 4 on the numerical setting and then increase the gain from zero to get the desired picture. Any suggestions? Can you explain the graph in the TVG menue?

 

[Snips]

42Duffy,
Thanks for your question. The best way I found to describe how TVG works on a sounder is to envision how the Sea Clutter control works on your radar. Both controls help suppress stronger short range targets by lowering the receivers gain, thus giving us the term TIME VARIED CONTROL. I think you would agree that short range targets producer stronger returns than long range ones. As you have seen, these stronger short range targets can saturate a receiver which in turn leads to a very cluttered picture. One way to deal with these overly strong returns is to simply lower the output power of the transmitter, this works good for short range targets but the draw back is that you can lose most of your longer ranges targets. If we went the other way and kept the output power high but reduced the receiver overall gain the same thing would occur, loss of the weaker longer range/deeper targets. So what can we do? Well there is really only one option since we can't change the charactertics of a TX pulse after it has left the building, we can vary the receivers gain curve. Unlike a radar that only has one TVG (Sea Clutter) control, our larger sounders have two TVG controls, LEVEL and DISTANCE. With these two controls you can better fine tune a sounder shallow water performance in conjunction with your front panel gain knob. Your front panel gain knob sets a upper limit on how much gain the sounders receiver has. The LEVEL setting controls the receivers starting point (basically the face of the transducer), you can vary it from 1 to 10. Remember "Less is More", meaning the lower the numbers the higher the starting gain will be. The DISTANCE setting (I think it should be called Depth) sets a end point to the gains suppression. Out of the box, the DISTANCE setting is at 600ft which means you are suppressing the receivers gain out to 600ft. Below is a graph of the receivers gain curve. Hope this helps, if not let me know.

Snips

 

[Anonymous]

Hi 42DUFFY are you fishing in say 2000 ft of water and most of the time the tuna and bait are in less than 300 ft from the surface of the water and your trying to set your fish finder to read good in the first 300 ft of water? (im just trying to under stand and learn some thing new) Thanks Alm. :furuno

 

[Anonymous]

Hi Snips i think i understand what you are saying, I have a 1150 with a 2kw 208b8 and a 3kw 50 bl hr.When searching for cod in deep water 300/500meters i am using LF sould i have my TVG level at 8 or 1?. I have it at 8 which looks like i am suppressing gain up near the surface(which i have no interest in) and concentrating on the bottom 20m of water.
Does this sound right too you?.
Many thanks george

 

[Snips]

George,
You are correct, but really you only need to adjust the TVG level if you have unwanted surface clutter. If you don'thave any shallow (surface) clutter you can leave it at 4 or 5. The higher the TVG Level setting the more the suppression.

Snips