question about discrimination adjustment on analog detectors

[pulltabfelix]

just how did the discrimination knob(s) work on analog detectors back in 70's and 80's.

was it just to discrim out iron?

 

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[SD51]

Whenever someone asks me, "How does it work?", I always respond with, "Pretty Good!" Sorry, my Garrett Groundhog VLF/TR detector had an adjustable Discrimination knob with numbers from I think "1 to 10".
I would usually set it at a number that would just discriminate out pulltabs, so anything more conductive than a pulltab would produce a tone.
Bet I left a lot of Gold jewelry in the ground.

 

[Terry Soloman]

Back in the day, 1970s- early 1980s, I dug everything. With the Garrett, I was looking for silver coins and rings using high disc. With the C&G Wildcat I hunted gold nuggets, no discrimination.

 

[Carl-NC]

just how did the discrimination knob(s) work on analog detectors back in 70's and 80's.

was it just to discrim out iron?

Depended on the design, but most would vary from iron up through what is now a zinc cent. The technique used in TR-Disc was to vary the demodulator phase so that any targets below the disc point would give a negative response and any above the disc point would have a positive response. This resulted in the audio threshold blanking on a disc'd target and beeping on an accepted target. Unfortunately targets closer to the disc setting were also attenuated so, ferinstance, if you set the disc to "Foil" then nickel depth would suffer.

Some of those models were a dual mode TR-Disc/VLF-GB. You could have either disc or ground balance but not both at the same time because they only had a single demodulator. VLF-GB was just a special case of placing the disc point exactly at ground. Eventually they figured out that by using 2 demodulators you could have your cake and eat it, too.