IGSL

[Davor]

Perhaps. You could build a Fe channel with comparators stage, and audio stage too using, say, two chips and a few small bits? On the plus you'll have a real audio (unlike the two tone ... something ... for TGSL), and independent discrimination option that may enable you to get a super sexy IGSL 3 tone operation or a notch.
Yeah, tempting.
Perhaps it will be a way to go. IGSL have certainly proven the ENORMOUS advantage of independent Fe discrimination, but at this very stage it is still a TGSL on steroids. So if I remove and optimise the "steroids", silverdog makes a board to plug it into TGSL, you'll get a "blue pill" solution that will blow the existing TGSL's into the blue yonder and back. It could be done.

On the other hand, a redox IGSL is just an interim stage of something much better than TGSL.

I'm very sure my future project will have this dual discrimination, but I'm greedy and I wish it to be a 4-quadrant solution as well. We'll see.

Anyway, IGSL is very close to my hart and all my mods were done with the existing rigs on my mind. None of my mods require any changes on the existing PCBs.

[golfnut]

[QUOTE= I'm very sure my future project will have this dual discrimination, but I'm greedy and I wish it to be a 4-quadrant solution as well. We'll see. QUOTE]


I know good commercial machines have full wave/fourquadrand/balanced mixer/tayloe detectors. IGSL, IDX effectively have a single diode detector like an old AM radio (good its day)

If you wanted an IDX type unit with a single disc and Geb on way of doing it is like my sketch...

I too want to one day make something with that elusive 10" depth on a mid size coin,,

S

[Davor]

...way of doing it is like my sketch...

There is a bit more to it than just combining. Phase detection requires multiplication, not addition, but good thinking though. From olden Fishers onwards, including IDX, such addition is used for phase rotation. IMHO the TGSL/IGSL phase extraction technique is more robust with large signals, and that's precisely where I want to be. As it is now, my mods of IGSL extend the unspoiled discrimination for at least one decade north and south, and I'm sure Fisher-style phase rotation would be a limiting factor.

Extracting phases directly from Tx is very meaningful if you don't want to pursuit futile equality of the channels gain and frequency response.

[golfnut]

There is a bit more to it than just combining. Phase detection requires multiplication, not addition, but good thinking though. .

I think you missed a bit Davor...



The schematic is Only for a single Dic Ch. Recombining the quadrature signals gives you the amplitude increase while maitaining the phase information of the Rx signal coming through.

You Duplicate this schematic for the GEB channel.


Effectively making an IDX but GEB and Disc are Full wave domods you see. Like a good detector should!


S.

[Davor]

Exactly! The only missing detail is either a rectifier if you are into all metal, or a multiplication circuit that will narrow the response to a single quadrant.

You may achieve the rotation of phase response either by addition as per your sketch, or directly rotating the phases of the switchers' drivers. I prefer the latter because it is way more robust with strong signals.

[golfnut]

Exactly! The only missing detail is either a rectifier if you are into all metal, or a multiplication circuit that will narrow the response to a single quadrant.

You may achieve the rotation of phase response either by addition as per your sketch, or directly rotating the phases of the switchers' drivers. I prefer the latter because it is way more robust with strong signals.

Im a bit lost here how do you mean - with this statement..

I dont have a neat solution for these full wave puppies.




My aim is to get a sensitive solid quality Rx. That is what I have in sketch -

1)full wave quad demod - for a single Disc channel.

2)full wave quad demod - for a single Geb channel.

This would make an IDX in effect - but with sens and depth approaching a commercial mid range unit - rather than an 80s low end unit.


Thats my input , as ever its only opinion and I am wrong regularly.

[Davor]

OK, I understand.
To have a good rig you'd have to ensure low noise preamp that will not spoil (much) the noise floor set by the coil's resistance. You'll have to filter the input so that neither lower nor higher frequency components cause excessive EMI, and full wave helps here by removing the common mode signal and other artifacts caused by asymmetry. Gain blocks will manage over 100dB dynamic range and not introduce too much 1/f noise, yet you'll be able to swing slowly and still have a meaningful output. Phase comparators will do the least possible anti chatter garbage artifacts, delays etc, and your sound/vision/vibration interface will be just right.
If you also manage to fit some extra notch or MCU control for the knobology-challenged users - even better.

[golfnut]

Can we do a block diagram of what we all think we want.

Davor, your IGSL tweaks are not for extra depth are they.. they are for power consumption and large signal handling.


If we agree a block diagram with the system features we them we have a rough spec.


Once we have a product spec we can generate a system design - with parameters for each block - then you end up with the product we all wanted.

It may be a better way than pulling old schematics in from other forums.

S

[golfnut]

When we do the next kit - can we get the DISC and GEB POTS on the edge of the pcb - like in pic please.
Can we keep the Rx pre amp and the Transmitter circuits more than 2mm apart - with a sloid copper gnd rail between them, local decoupling. etc


Disregard the image on LHS It is error - and I cant remove them once on..

[Davor]

Can we do a block diagram of what we all think we want.

Davor, your IGSL tweaks are not for extra depth are they.. they are for power consumption and large signal handling.

A block diagram is a good idea. Eyeballing a schematic is fine for a well trained eye, but not for everybody else. I'll make it ... some time.

As for depth, there is a mod that does affect depth and discrimination precision, and that is omitting capacitors and resistors in final Disc gain stages feedback. There are only antiparallel diodes now, and they extend successful discrimination, and depth. By virtue of signal symmetry in final GEB stages a few dB-s are gained in the comparators stage, so YES, these mods did improve depth. My input preamp sucks though.

I'm playing with a better preamp that will give some 10dB more. That one could be made as an add-on. This is not a mere speculation because the existing solution is over 10dB noisier than the coil can provide.

That would be the last modification I intend to exercise here. One must be able to say "enough" once everything works good.

[peterr88]

I got a ITGSL board just never got round to constructing it

[satdaveuk]

I got a ITGSL board just never got round to constructing it

Dito

[Davor]

You have no idea what you are missing

[ivconic]

I am buried deep in various commitments lately (autumn... what to say?) so i delayed my further work on IGSL at least till winter.
However; i am collecting all the modifications done here and intend to apply them on my IGSL's i have here.
IGSL is not finished story, it is half way there.
So i am glad that Davor is showing good will to continue improving it.
That job is not for nothing, because i have serious intentions for later, to transfer IGSL into "digital" world.
So once we get most optimized IGSL setup; next step shell be "digitalization".
Not so soon. Maybe next year.
So all you done here so far is not wasted time.
Later will be easy to apply adds on existing setup and continue with quite decent machine.
Davor don't throw away second GEB channel because we gonna need it.
Cheers!

P.S.
For Christ's sake DO apply shield on your coil!

[Davor]

I think the only sensible purpose for the other GEB channel would be an all metal channel with slower motion response. However, I strongly believe that lowering the high pass response in the rest of the channels would do the very same job but better because of the discrimination. Other than for the increased 1/f noise - there is no reason not to lower the high pass cutoff. So instead of 4u7 to go for 15u or something. That would give you the best of both worlds, and without additional knobology. In such case you may completely abandon the other GEB channel and embrace full wave switching instead.

As you can see I did not make changes to the very frontend (yet) and I intend to maintain the FKK coils as a project on it's own. I can't expect commercial coils to adopt this approach any time soon, and many people are not into building their own coils. So shielded coils frontend there is.

BTW, for shielded coils it is better noise-wise to ground the inverting input side of the coil as you suggested once. It has no common mode suppression then, but you rely on the shield and there you have it.