IGSL

[golfnut]

IGSL Building

I would say dont buy an IGSL or TGSL until you have read Dons write up on this project.

Use this info to decide If this is what you want and can build.

I built mine months ago and only just got around to reading it.



Id say the nulling I did with a meter is not that good - the flaw then is poor GEB on Fe channel - on my IGSL. - Run out of adjust range -rejecting ferrite doesnt happen.



Plus the initial phase relationship of the Tx signal to the leaked Rx signal isnt within the
+/-20degree range. Need to check this around nulling time.


In use with Fe reject max, Fe sens min - I still get both tones on most Iron targets.

I can hunt with it but its not as good as it could be.


S

[Vladd]

Is this similar?

http://www.youtube.com/watch?v=IuETHmjBK-Y

[6666]

Hi Don

use scope on TX and RX and adjust for +/- 20 degree phase shift, as per Don Bowers excellent article.

This one about phase shift
thanks

[dfbowers]

In post #1025 there is a reference to Don Bowers excellent article on phase shift
I have searched through the thread but could not find it, maybe missed it
but does anybody have a copy please , thanks
6666

This one?

http://www.geotech1.com/forums/showthread.php?t=15710

Good thing Qiaozhi made it sticky!

[6666]

In post #1025 there is a reference to Don Bowers excellent article on phase shift
I have searched through the thread but could not find it, maybe missed it
but does anybody have a copy please , thanks
6666

[golfnut]

1) I had my Fe channel with no rejection of ferrite...

- Field Test - It doesnt matter, ground balances ok as it is on Fe Channel


2) I have a oscillation the comes and goes - blips the Non Fe channel.

- I erected a Copper screen/fence to sheild the Rx preamp- --- This helped but not enough.

_ I wrapped copper tape aroun the 3 P1 pot wires and grounded it --- this helped when I poke finger in nearby and previously I got a blip, now quiet. Not enough..

- Added 0.1uF to + and - rail on U4 - not enough

- added 1Meg FB resistor to U4a - samll improvemnt - not enugh.

Osillation more consistent repetition rate now.


- Dabbed a cap on the -ve rail and the rate of oscillation changed ?


Tried 1000uF on the -ve rail local to U4 - Sorted.

It is much more settled now.

It does oscillate if you turn P3 up some more non Fe gain up or Iron Gain too high.

I can easily get a Uk 20p buried 15cm in wet clay soil / with small amount of grass on top.


Im doing a roman villa on Saturday with it - look a proper charlie with it oscillating away next to 40 etracs

S

[Qiaozhi]

Also why is this an inverting input?

Because the top section is designed to reject ferrous targets, and the bottom section is designed to reject non-ferrous.

[golfnut]

Better Picture..

[golfnut]

what confuses me..

The non ferrous channel works really well.


The ferrous channel I cannot get rid of any size or type of ferrite and have SOLID Iron GAIN

Why iis U7d an inverting input ???? Is it this difference that makes it an Fe channel???

Or is it an error common to all???

I have a dig on a villa on Saturday and I would like to get it all singing well

Plus I redid the preamp resistors to 330 and 15k (same gain lower noise)
I feel the range has improved - I will get some numbers.

ATTACHED ERROR PICTURE
SEE NEXT POST PIC

Steve

[bernte_one]

hello golfnut

i dont look at shematic but i can say that i´m able to tune geb so that ferrit is not shown
i only can say that it is easier to reject a small ferrit instead of a big one
but i think it also depends of the ferrit material

if you have problems to reject ferrit check if tx and rx a right connected try reverse one side
check if the one with shield is connected right point to pcb
igsl also works when coil is wrong connected
but first what i see when wrong connected is a higher null voltage level and more sens to small objects- and also ferrit

regards

[golfnut]

Ferrous GEB IGSL - schematic error?

All, IGSL.

My one I can get good high tone on the Non Ferrous - reject to Ferrite ie GeB is tunable and ok.


Ferrous channel always sees the ferrite - never been able to reject it.

If you look at schematic the disc channel has u7b and U7a both are non inverting inputs.
This channel is good.


The Fe block U7d and U7c have one -Inv input and one + Non Inverting input
This channel dont GEB

Is the schematic wrong ?????

Should U7d pins 10 and 11 be swapped over??

[der_fisherman]

I dont know whos in charge of updateing these files but it needs to be done because its going to catch alot of people out, was so lucky just ordered aload of stuff about 2 hours before desided to have a ponder here, and there it was, lucky for me in one sense because I would have been looking for faults like these lads, proberly spent hours on it, id be well peed off.
Trouble is I need to make orders over £100 to get good prices with no postage charge and although there was only 2 hours in it they wont budge because the order was already prosessed.
Im not pointing the finger here oviously wasnt done on purpose, infact maybe its a wake up call to check and double check component specifications are selfs in stead of takeing them as gospal.
Anyway all the best ive calmed down now lol

Take care
Regards

I agree with you completely and I feel that this is also a point which we should be also considering when picking a schematic/CAD package, where the parts list is automatically generated and everything can be covered by version numbers.......

I have talked about this before and many have commented, but we have not made any final decisions......maybe we should!!

Regards

Andy

[satdaveuk]

Dont take this as gospal but checking the spec sheets there is MC14066, HEF4066BP, as well as the CD4066 all run between 3-15volts im sure will do the job, Shall order 2 of each and varifi ok.

Thats when ive built it mind you

Regards

[satdaveuk]

I dont know whos in charge of updateing these files but it needs to be done because its going to catch alot of people out, was so lucky just ordered aload of stuff about 2 hours before desided to have a ponder here, and there it was, lucky for me in one sense because I would have been looking for faults like these lads, proberly spent hours on it, id be well peed off.
Trouble is I need to make orders over £100 to get good prices with no postage charge and although there was only 2 hours in it they wont budge because the order was already prosessed.
Im not pointing the finger here oviously wasnt done on purpose, infact maybe its a wake up call to check and double check component specifications are selfs in stead of takeing them as gospal.
Anyway all the best ive calmed down now lol

Take care
Regards

[der_fisherman]

Dito
I just ordered all the bits for this project from various supplyers , guess what? ordered 4, 74hc4066 why has it took till now for someone to pick this up, and why wasnt it mentioned in the latest parts list, Must admit though had a gut feeling about this chip just 4066 didnt ring true.
Reason why it gets hot because its designed to work between 2-6v, the cd4066 works between 3-15v , easer to be wise after the event.
Proberly find its been mentioned before on here just missed it

Hope all is well

Regards

I have never seen it mentioned before, though it is REALLY important.....
regards
Andy