Author Topic: SwitchFire / TVG  (Read 5794 times)

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Offline George

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SwitchFire / TVG
« on: November 14, 2009, 02:04:44 PM »
It appears that the older I get the dumber I get. 

This weekend I was reviewing some recordings on my computer with HumViewer, I had a short recording and spent time reviewing it in detail.  After several reviews I realized while I was viewing a lot of fish on the computer screen,  I was not seeing them the 1197.  So I took the computer out to my boat and played this recording on the computer and on the 1197 at the same time.  Wow, I had been using the Switchfire (TVG) in clearmode and was not seeing the fish arches, I changed Switchfire to Maxmode and it showed the same fish arches I was seeing on the computer.

I wonder if it would be possible to have a sliding scale to adjust the Switchfire or does it have to be all or nothing?

When in clearmode the screen is pretty clean showing the bottom structure and in maxmode the screen is very cluttered on the 1197 while the computer screen is clean while showing the fish arches.

I will spend more time with the computer and the 1197 side by side to better tune the 1197 for finding fish.  This makes me wonder what else I am missing.

George
 


Offline Humminbird_Greg

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Re: SwitchFire / TVG
« Reply #1 on: November 14, 2009, 07:03:44 PM »
It is possible to have a sliding scale for the TVG/SwitchFire menu if they would just program it so.  This is the first comment I made when I first saw the TVG menu: "why didn't they make it an adjustable scale?".  Maybe it will get added in a later software update but I'm not holding my breath for it!  LOL!

Greg Walters at Humminbird
gwalters@johnsonoutdoors.com

bobcoy

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Re: SwitchFire / TVG
« Reply #2 on: November 14, 2009, 08:31:19 PM »
Maybe I am missing something also. I was under the assumption all I had to do was adjust the sensitivity down to the amount of clutter I was comfortable with while in the max mode.  Bob

Offline Humminbird_Greg

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Re: SwitchFire / TVG
« Reply #3 on: November 16, 2009, 11:46:31 AM »
You can Bob.
Not sure that I really understand your question though.

The Sensitivity and TVG (SwitchFire) menus perform different functions but they both appear to do the same thing to you the end user; show more or less ‘stuff’ on the display.

Greg Walters at Humminbird
gwalters@johnsonoutdoors.com

bobcoy

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Re: SwitchFire / TVG
« Reply #4 on: November 16, 2009, 08:33:17 PM »
Thanks for the reply Greg. I guess my question was, Isn't toning down the max mode the same as a sliding scale on switchfire. It sounds like it is not from your response. I will continue to experiment with it. I for one like the max mode because, at least till now I was confident I was not missing anything. I guess that is part of the fun to experiment and compare. Bob

Offline Humminbird_Greg

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Re: SwitchFire / TVG
« Reply #5 on: November 17, 2009, 02:15:00 PM »
Bob,
Setting the SwitchFire menu to the Clear setting will turn on the TVG (Time Variable Gain) feature in the unit.  Imagine the TVG as the Sensitivity being turned way down near the surface of the water and than for every few feet deeper from the surface, it gets turned up a little more until after a certain depth the Sensitivity is turned all the way up to wherever you have it set.  This helps prevent fish that are close to the transducer from showing up as a larger target since they would reflect more sonar back to the transducer than the same sized fish would if it were farther away.  Think about it this way: if you turn on a flashlight at night and shine it on someone who is only a few feet away, they will reflect most of the flashlight beam back to you.  Have that same person move 20 feet away and they now don’t reflect as much light back to you as they did before – the same thing happens with sonar.  Now if you could somehow filter most of the reflected light out of someone standing a few feet away from you and have it match the same amount of light being reflected back to you by someone 20 feet away, than you would have a TVG system for a flashlight.

As the water gets deeper the time it takes for a sonar signal to go down to an object and get reflected back increases – this is where the Time part comes from.  The Variable part comes from the fact that the settings varying according to the water depth (or Time).  The Gain part comes from the fact that it’s the Receiver that gets this adjustment (although this is all done digitally).

When we vary the Sensitivity menu setting, we are not really adjusting any part of the unit’s receiver or transmitter.  Since everything is digital what we are doing when we turn this menu up, is telling the computer that we want to show sonar signals that were shown with a weaker color to now be shown with a stronger color.  The opposite is true if we turn the Sensitivity menu down.

Greg Walters at Humminbird
gwalters@johnsonoutdoors.com

bobcoy

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Re: SwitchFire / TVG
« Reply #6 on: November 17, 2009, 03:35:38 PM »
WOW! I have a much better understanding of TVG. Thanks Greg

Offline Jolly Roger

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Re: SwitchFire / TVG
« Reply #7 on: November 21, 2009, 10:42:38 AM »
Thanks for the explaination Greg,
I was also wondering how this is related or connected with each other. Now it's clear  ;)

Regards / Harry
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