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fisher f75ltd2 pinpoint sounds funny
- Thread starter basstrackerman
- Start date
Mike Hillis
Well-known member
Hi, Basstrackerman,
I just now watched your video. Sorry I didn't make time to look at it sooner. I only have dial up at home and at work it can be difficult to watch/listen to a video.
That pinpoint phenomenon is called an overshoot null. It went quiet right after it passed the peak of the target response, then reset. The F75 reset is extremely fast so that it is resetting while still over the target which gives that momma response.
Can you switch over and test it in both AM and STATIC modes and see if it does the same thing? Shallow and at max detection range.
If you raise your coil a bit higher off the ground, does it still do it? Just want to see if this is only happening in the coil's non-conformity area or does it still happen at distance.
Most detectors that suffer from overshoot nulls only do so in the non-motion all metal mode and the null will stay in place until it resets or another target is detected, which ever happens first. It is really only bothersome if the reset speed is slow. It is linked to the additional filtering that takes place to provide TID in the non-motion all metal mode. The F75 reset speed is so fast that the main affect noticed is the audio stutter that results in the momma sound.
The question about an overshoot null is, "is it useful?" The answer is yes or no depending on a couple of factors:
1) If your machine has a slow reset speed, then the answer is no. No because you cannot use the no-motion all metal mode to size an object. You only hear the ramp up and peak response, then it goes silent until you go over another target or the machine resets itself. The all metal mode is useless for target sizing, but works fine for pinpointing the center of a target.
2) If your machine has a fast reset speed, the answer is maybe. I say maybe because if the overshoot null stays in place at depth, then it is useful for separating out deep small targets in close proximity to each other. If the overshoot only stays in place for the signals that are strong enough to kick in the TID filtering, then it is not useful for that task because you wouldn't be able to tell if you were over multiple deep targets or just resetting over a larger shallower target. But again, in that scenario, you would able to hear and differentiate TID range vs non-TID range targets. Toss up. Either way, on a fast reset like the F75 has, you can still size targets. Just sounds different. No affect on actually pinpointing of a target.
Two ways to look at it. Defect or feature. Once you know what it is, you know how to use it. Hope this information helps.
Again, sorry for taking so long to look at this post.
I'll look at mine tonight and see if she exhibits the same affect.
HH
Mike
I just now watched your video. Sorry I didn't make time to look at it sooner. I only have dial up at home and at work it can be difficult to watch/listen to a video.
That pinpoint phenomenon is called an overshoot null. It went quiet right after it passed the peak of the target response, then reset. The F75 reset is extremely fast so that it is resetting while still over the target which gives that momma response.
Can you switch over and test it in both AM and STATIC modes and see if it does the same thing? Shallow and at max detection range.
If you raise your coil a bit higher off the ground, does it still do it? Just want to see if this is only happening in the coil's non-conformity area or does it still happen at distance.
Most detectors that suffer from overshoot nulls only do so in the non-motion all metal mode and the null will stay in place until it resets or another target is detected, which ever happens first. It is really only bothersome if the reset speed is slow. It is linked to the additional filtering that takes place to provide TID in the non-motion all metal mode. The F75 reset speed is so fast that the main affect noticed is the audio stutter that results in the momma sound.
The question about an overshoot null is, "is it useful?" The answer is yes or no depending on a couple of factors:
1) If your machine has a slow reset speed, then the answer is no. No because you cannot use the no-motion all metal mode to size an object. You only hear the ramp up and peak response, then it goes silent until you go over another target or the machine resets itself. The all metal mode is useless for target sizing, but works fine for pinpointing the center of a target.
2) If your machine has a fast reset speed, the answer is maybe. I say maybe because if the overshoot null stays in place at depth, then it is useful for separating out deep small targets in close proximity to each other. If the overshoot only stays in place for the signals that are strong enough to kick in the TID filtering, then it is not useful for that task because you wouldn't be able to tell if you were over multiple deep targets or just resetting over a larger shallower target. But again, in that scenario, you would able to hear and differentiate TID range vs non-TID range targets. Toss up. Either way, on a fast reset like the F75 has, you can still size targets. Just sounds different. No affect on actually pinpointing of a target.
Two ways to look at it. Defect or feature. Once you know what it is, you know how to use it. Hope this information helps.
Again, sorry for taking so long to look at this post.
I'll look at mine tonight and see if she exhibits the same affect.
HH
Mike
Mike Hillis
Well-known member
Just following up. I don't experience any overshoot nulls.
Resets may clear it up.
Again, with a fast resetting machine like the F75, the only real affect will be that momma stutter over the peak response. If the pinpoint audio response in those modes doesn't bother you I'd treat it like a feature. If it is too much for you, multiple resets may clear it up
If it is just totally unacceptable for you give Fisher a call and see what they say.
By the way, if you want to experience an overshoot null with a slow reset, try a Tesoro Cortes in it's non-motion all metal mode. That detector has at least a 1 second delay, maybe even a 1-1/2 second reset delay and was considered normal operation.
HH
Mike
Resets may clear it up.
Again, with a fast resetting machine like the F75, the only real affect will be that momma stutter over the peak response. If the pinpoint audio response in those modes doesn't bother you I'd treat it like a feature. If it is too much for you, multiple resets may clear it up
If it is just totally unacceptable for you give Fisher a call and see what they say.By the way, if you want to experience an overshoot null with a slow reset, try a Tesoro Cortes in it's non-motion all metal mode. That detector has at least a 1 second delay, maybe even a 1-1/2 second reset delay and was considered normal operation.
HH
Mike