Need some ideas on P.I front end

[Unregistered]

JC1

Oh they shorted every receive turn.

I just woke up so little slow right now.

Oh the damping resistors, getting hot, use enough they

don't get so hot, input gain resistor gets hot too.

in the standard configuration.

[Ferric Toes]

I don't get

the thirty switches thingy. disconnect every turn? what for?

huh? really? this does something? gets government funding?

I'll have to find that patent again, but I think it is so that each switch is only subjected to one turns worth of back emf, so it won't blow. I'm sure such a project could eat up quite bit of funding and research time.

Eric.

[Unregistered]

JC1

Good Morning or Afternoon Eric,

Thanks for the response. Didn't know you were on line.

Great. ok. how about non inverting op amp. then input resistor doesn't get so hot. hehe.

disconnect damp resistor since it is now just loading, the rec coil, and wasting the return signal.

of course don't want to disconnect it until emf is completely damped , completely.

this might be a problem.

[Unregistered]

JC1

Hi Eric,

Hey don't go any trouble looking up the patent. Lots of patents around.

I think I get it now. Kinda. Not going to try it, interesting though.

But disconnecting the input can keep from slaming the amp to the rail, even with diodes, as you well know.

Yea, I come here lurking sometimes, skim the posts.

Maybe misreading things sometimes, not thinking at other times.

hehe.

Thanks Eric, and thanks for all the information over the years.

Good of you to share.

[Ferric Toes]

Good Morning or Afternoon Eric,

Thanks for the response. Didn't know you were on line.

Great. ok. how about non inverting op amp. then input resistor doesn't get so hot. hehe.

disconnect damp resistor since it is now just loading, the rec coil, and wasting the return signal.

of course don't want to disconnect it until emf is completely damped , completely.

this might be a problem.

Hi JC,

I was just in the middle of ebaying a few things, when I saw you posting. You better go and get another cup of coffee to get fully awake. Input resistor will get just as hot with a non-inverting amp, because in both situations you have to use a protection diode, and this is where the current is going. Not sure about the damping resistor loading the coil when receiving. You have to damp the coil to keep it broadbanded in receive, so as not to distort the decay curve.

Eric.

[Unregistered]

JC1

Hi Eric,

I guess I meant in the case of having a say 300 ohm damping resistor across the coil and then a 1k ohm input resistor, back to back, or back to front, diodes (depending on how you grew up) the 1k gets hot too.

Non inverting the 1K is,, well you know.

But still have to limit the current throught the diodes with something, so,,,.

thats what I meant, and you are right, disconnecting the damping resistor turns the rec coil and any capacitance into a tuned circuit, now where it is tuned and how wide the band is , is something that could be investigated.

Will it effect the decay curve? you bet it will. But if you are just detecting. metal there or not there.

Third cup.

[Ferric Toes]

1956 Coil Switching.

Hi JC,

Tried to email this to you - no go. Tried to post on this forum - no go. So I posted it on the PI Forum instead.

http://www.findmall.com/read.php?34,...714#msg-323714

Eric.

[Unregistered]

1956

Hi Eric,

Thyratron? Accumulator?

These guys are right, back to the 60s.

Acc is somekinda integrator?

Thratron is a switch?

I thought you guys used valves? hehe.

Thats what we need a good fast valve!!!

I will see if I can post.

[Unregistered]

JC1

Hmmm,,,, have to take a look. In the mean time, out of the box.

Maybe we don't want broadband, most receivers don't, have to trade off if we get more signal or more noise.

I'm just throwing out blue sky here, get people thinking.

I know I don't want need 50/60 hertz, and what is all that higher frequency junk riding on that sign wave.

did I say sign wave, anybody take a look at that sign wave?

yuk!!!

but then if we start using the cap of the coil and make a lower Q antenna of smaller bandwidth then the system will get sensitive to changes in this capacitance and blah blah,,,,,,

guess have to stick to the 60s stuff.

Eric, your circuit, I will take a look. Solution should be hard or you would have already found it.

JC

[Unregistered]

JC1

Hi Eric,

Oh my Yes, this is what we want to do.

Very good!!!


I made a ringing coil detector once, rang the heck out of it.

Of course if you bring metal near it, the ringing changes..

Of course the ground and just about everything else (your body) makes it change too.

But it was very sensitive to metal. If you could micro the waveforms compare em,,, blah blah.

Sure it would have been extra temperature sensitive as well.

[Unregistered]

JC1

Hi Eric,

Now how is the best way to realize this circut?

Or realize the same benefit with another configuration.

1956, things were harder then, every switch or amp

was a pain. Not which op amp has lowest noise to drop in.

Made people think about the problem more.

Eric you've seen it all.



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"You can't beat a man at his own game" - Some Smart Guy