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« Letzte Änderung: 14. Januar 2014, um 16:50:31 Uhr von (versteckt) »
Sven: I was playing around with a new build today. Going back and forth with a jumper and the 1K resistor in a header socket, just to see how much difference there is between double the gain with the jumper and the 1K.Tough decision, since I hunted with the jump in place all last year. Guess I got used to adjusting for EMI? Which I thought wasn't bad overall, since I hunted mostly with the 7" coil. Tuning was a bit touchy with the frequency control. To me this was not a big issue, might be for the first time user in the field if the Gain pot was turned up past 50%. Especially when using the 10.5" coil. Larger coils tend to be prone to picking up some more EMI.Today on the bench, air testing, I have come to the conclusion that the 1K resistor is the way to go. It's much more stable. Being much more stable provides a clearer signal on a gold ring at the deeper range. Less noise to interfere with the signal at the same ruler depth as with the jumper in place. So you get about the same depth with the 1K, maybe 1" less. But, you can hear the target. Also, seems a bit more sensitive to the small nugget used for testing. Going to be switching the jumper out of last years build for the 1K.
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« Letzte Änderung: 15. Januar 2014, um 11:00:28 Uhr von (versteckt) »
« Letzte Änderung: 16. Januar 2014, um 11:00:56 Uhr von (versteckt), Grund: R42 Trimmer 20k »
Here's a quick change out and you won't need to calibrate using a scope.Per Smitty:The setting up of this pulse delay for the Second Sample pulse is really not critical. I would like to make a suggestion here that you remove the Second Sample Pulse delay trimmer and replace it with a 8.2K resistor. This trimmer is located at the bottom of the second 74221 on the left side of the board. This will cause the Second Sample to take its sample about 85us after the Target Sample pulse. I was going to remove the trimmer and add the 8.2k resistor but I forgot. The fixed resistors tolerance is plenty accurate enough for this pulse delay. The Scope is not necessary. The idea here is to take this sample far enough out that there can be no gold signal in the sample. Anything over 80us will work.Since I don't have any metal film resistors that are 8.2K. I am going to solder in 2 resistors in series that equal 8.3K.If you need to, you can go the same route.
Technik
