Fisher "F" Series Forum

The F 75 is said to run 2 separate circuits 1 - audio 1 - TID circuit.
Now i know we have heard and read , go by tone first and numbers second and this is true 99% of the time .
Many a time i have a jumpy number but good audio and make a nice find.
Only on a very few targets has the reverse happened with bad audio but a solid number
Hunting in the winter a few years back with a friend, i passed a target that was real scratchy to hear but had a stable TID . I had my bud sweep it with his tone only
machine using a smaller DD coil than mine , said it was a no dig target.
I had to chip through the frozen ground to pop out a Indian head penny. Rescanning the hole showed plenty of iron at this old site , no surprise there
Not sure why the machine did what it did and have only seen this a few times.
Have you seen this happen to you . Thanks Mike .

I don't think the F75 (or T2 for that matter) has two seperate circuits. Its more that (depending on which audio mode and process you are using) the audio and target ID meter are showing two different ways of analyzing the signal from the same circuit. The audio is in "continous mode" to use the lingo from the manual, while the target ID meter is in sampled mode. In other words the audio is playing a continous moment to moment signal of what is coming in from the coil and the audio changes in real time as the signal from the coil changes as it moves over the ground. The sampled mode the target ID meter uses just takes a snap shot of the signal when it is at maximum signal strength. The manual doesn't say how long the window of time is for each time it updates the target ID but as we all see when using the machine it is not very long and so the meter does change very frequently even though each time it changes it is displaying the signal at the moment of maximum signal strength for each sample window.

So in your case the good target had a higher signal strength than the surrounding iron and so the meter locked on to that signal while the audio was continously changing and so playing audio from the iron mixed in with the audio from the injun.

At least that is the way I read the manual. If I am wrong hopefully Dave J can jump in and explain it properly.

Good explanation, Steve.

--Dave J.