lobo improved

[porkluvr]

Try this?

Maxbiri, I wish I had thought to ask you what frequency you have set.
I have the freq.pot set at 50% and have tweaked parallel (parasitic) properties of the 10mH coil so that I have a good peak
using a 4.7nF tank cap. Adjusted drive pot for a -reasonable- combination of amplitude and waveform symmetry.
TX setup is complete (fo=20.4kHz).

Here is how I would set the RX phase:
The russian (?) drawing shows 8.2nF parallel in the receive tank. Give it a try.
Maybe the cap marked 250pF is actually supposed to be 25pf? I try that.

According to your schematic, you have placed 100k resistor across the GCX pot. Remove it, or put it from the BOTTOM terminal to the wiper.
That makes a big difference. 100K gives 35 degrees of adjustment. 300k increases the range to about 48 degrees.
A whopping 55 degrees of GCX adjustment results from removing the 100k altogether.

Probably better to use 10k resistor instead of 100k on the LM393 input(s).

Now, take a look!!! One of the coil's leads may need to be reversed - one day maybe I understand why. Not today.
***********************************
The red trace is the RX output. Purple (it looks brown) is GCX ZCD output, knob turned CCW. Orange is GCX ZCD, knob turned CW.
(I hope CW and CCW are not reversed. I find this all very confusing.)

I think this is pretty close to what is supposed to happen, except that I would delay rx signal maybe 3 more degrees?? Changing the 25pF to 33pF
would take care of that. Maybe it's not necessary, but would assure that received signal of neutral soil is within range of GCX CW adjustment?

Putting a 250pf capacitor across the 48k7 resistor shifts the rx signal about 45 degrees to the right. I think that would ruin your GCX channel's response.

I thought I had this thing figured out before? Um,hmmm. That shows how easily I can fool myself. If this setup is wrong, I hope
somebody will explain why. I have no scope to check this stuff in real world.
I might have the CW to-the-left and CCW to-the-right movement mixed up, I dunno.
Heck, this whole thing might be wrong, but it looks good from where I see it.

[simonbaker]

Hi Simon

I forget said that all my test are done feeding tx stage at 5v so all circuit can be powered at 9 volt, 6 AA or AAA battery or even a single 9v block so i presume a light device.
With new power stage i have a stable simmetrical +/- 4.95 volt, less than 5 mv difference.


Bye Max

Ok, 5v quite different from 8v -- I think you have 40% less coil current and lose some amount of depth because of it, no?

Regards,

-SB

[FOMA]

Hi maxbiri.
I did so:
L (Tx) - 1,33mH ; R(Tx) -11om
C = 47H f = 17,5 kHz

[maxbiri]

Hi all

@ porkluvr
where is russian schematic with 8.2 nf on rx coil? i havent it.
you are right r36 and 50 are 10 k on pcb, i forget again 100k on schematic, i will correct it.
I change c 13 from 100pf ceramic NPO type to polyester 2.5% and c 47 from 47 pf ceramic to 47 pf polyester 5%, i'm no able to find 50 or 51 pf, i think is not a problem few pf of difference.
I take off r40 and schortcut r37 and removed r49.
Seem there arent difference respect before.
About 250pf condensator i think is correct, if you look at diablo schematic, that have the same input stage, they use again 250 pf.
Now i' m schielding coil with grafite, alu dont work well.
This evening i hope restart with new test and try take same photo from oscope.
@ simon
At this first step i'm driving coil at 5 v, after when i will solve problems i will drive tx stage at battery power, if you look at my schematic i put a jumper for select 5 v or battery power for driving bc307.
@ foma
I have tried even as you suggest, using 1.3 mH as tx with 47 nf and rx 10 mH with 4.7 nF, it work in yhe same way, when correctly set.

Bye Max

[simonbaker]

Hi all

@ porkluvr
where is russian schematic with 8.2 nf on rx coil? i havent it.
you are right r36 and 50 are 10 k on pcb, i forget again 100k on schematic, i will correct it.
I change c 13 from 100pf ceramic NPO type to polyester 2.5% and c 47 from 47 pf ceramic to 47 pf polyester 5%, i'm no able to find 50 or 51 pf, i think is not a problem few pf of difference.
I take off r40 and schortcut r37 and removed r49.
Seem there arent difference respect before.
About 250pf condensator i think is correct, if you look at diablo schematic, that have the same input stage, they use again 250 pf.
Now i' m schielding coil with grafite, alu dont work well.
This evening i hope restart with new test and try take same photo from oscope.
@ simon
At this first step i'm driving coil at 5 v, after when i will solve problems i will drive tx stage at battery power, if you look at my schematic i put a jumper for select 5 v or battery power for driving bc307.
@ foma
I have tried even as you suggest, using 1.3 mH as tx with 47 nf and rx 10 mH with 4.7 nF, it work in yhe same way, when correctly set.

Bye Max

Thanks for info; I understand your approach with voltage for now, so we shouldn't worry too much about depth yet.

Looking forward to continued development of the circuit. Hopefully it will eventually work like original Lobo, because that is a detector I would like to try building some day, so very interested in your success.

Regards,

-SB

[porkluvr]

Foma posted a scat elsewhere, but I couldn't locate it to post its link. But, since I've made some additions, I may as well post it here - although I don't like it's large size.

I will try anything that works. I have problem because I want to build Lobo - but designing around a Silver Sabre coil, and with a Golden Sabre oscillator (tuned to 21.6 kHz) using +/-5V oscillator supply. The TX reference is C coupled to an active low-pass filter which drives the discrimination and GCX phase reference stages. I use GS oscillator because I can heterodyne the TX coil frequency against oscillator of LTC1044A voltage converter, and extract 500 +/- 200Hz audio (?!). Lobo TX is not good for that due its coil not being a frequency determining device.

I'll eventually, probably, wind a Lobo coil and replace the tank caps. But design basics are the same whether I do or not. Consider that all I had before were "?" for tank capacitance values; so what's the difference If I've redesigned the coil circuits?

Even though I have gotten away from the original design (and because of that) I need data from your project for reference. I use your "New Image Lobo" along with scat posted by Shawn Goddard as starting point... . Using 25pf cap instead of 250pf, while using 8.2nf at the coil seems to make everything good, in my perception. That is what I now use as baseline for my design. I may have ill-conceived notion about what is "good", but that's where I am. I was running out of ideas. If it doesn't work then I will make changes.

I take off r40 and schortcut r37 and removed r49.
Seem there arent difference respect before.
About 250pf condensator i think is correct, if you look at diablo schematic, that have the same input stage, they use again 250 pf.
Bye Max

R49 not so much affects total discrimination as it affects taper of potentiometer it is attached to; degrees phase reference change per rotation of dial. You'll still have almost exactly the same amount of phase change between 0%~100%, but the gradient will be different in-between.

You could parallel a 27p or 30p cap across the existing 250p for a quick test, but I'll shut up.

Well, anyway, good luck. If I ever get mine built I'll be sure and let you know how it turned out

[maxbiri]

Hi porkluvr

Thans for shematic, i will study it.
If you need same measures i can take them on my board, i have a dual traces oscope.
I measured current of oscillator and have these results:
3mA at 5 volt with a indirstorted signal of about 9 v PP
40 mA at 12 volt with again a signal of 9v pp
these are current values that feed final transistor of TX, all circuit, without final tr, drink 15 mA.
Seem that change from 5 to 12 volt have not good result; i found this very strange but need more test.

Bye Max

[porkluvr]

Seem that change from 5 to 12 volt have not good result; i found this very strange but need more test.
Bye Max

Max.
I think I have seen four different Lobo schematics, and wonder if some of them aren't rehashes of previous drawings - perhaps perpetuating any earlier mistakes? How many are actually based on tear-downs? And, I have seen not even one oscillograph of Lobo waveforms. To see some good dual trace shots of the GCX, DISC and received signals would be MOST helpful. I suppose having them well labled and explained, would be out of the question.

I have not really studied the schematic that I provided, only glanced it over. There may be errors. Don't believe everything you hear, (and only half of what you see)!

Your 40 ma with 12V sort of doesn't make sense - but stranger things have happened. (But maybe you meant 4ma?) Does that include the 555 current?
A while back as I experimented (in my virtual lab) I had a "good" setup with 8V supply. But always wanting more - I applied 10V and tried to dial in the circuit. Not good. I forget exactly what it looked like but had high distortion. Could not get more usable output than with 8V! I gave up on that 10V project. Maybe you should keep that mind as you try to use 12V!

I did bump up the frequency to 30kc or so, and, surprisingly, got it to look good with 10V power supply! Decided against trying to prototype at 30kc; thought it best to learn with ~20kc. I am again working with 10V, but as stated previously, hacking the Golden Sabre " Colpitts" oscillator. It seems to be fairly managable at ~21.5kc with 10V supply.

I'm curious, what frequency are you pumping?? Also, where are you measuring current to TX? Masuring current is very easy to do in spice, not so easy in real life. Did you measure voltage across emitter resistor? (I=E/R)

With 5V supply, your 9Vp-p seems pretty good. In my spice lab I could get 10Vp-p, but that is not real life. Various unknowns are at play.

Any oscilloscope pics you can post would be good. If you have problems you may be able to get assistance from one of the engineers or service technicians reading this.

I have a "toe hold", but still, many questions about how and why Tesoro IBs function. Good oscillographs with explanations are hard to find. Ivconic's "Golden Sabre Light" thread has yielded good information. At the risk of getting trapped into thinking in generalities, I have based my perception of the Lobo upon information available about other Tesoro models (such as GS, various Silver Sabre models, Eldorado, and Bandito). Sometimes it's hard to seperate facts from BS, but until I have an actual test bench and room to work - LTspice and what I have read are all I have to go on.

Bye

[maxbiri]

Hi all

In these days i'm tryng to calibrate oscope and built a simple L-meter for testing coils.
I found that 7555 generate a square signal not costant, i put a 100nf capacitor from ground and pin 5 but not solved the problem.
Now i post 2 sample photo take from oscope, this is the best i can do, sorry graticula is not visibile.
First one is signal on tx coil 10 vPP, good sinusoidal, if i increase power driver on tr base signal began distorted on top side, second photo.

Bye Max

[simonbaker]

Hi all

In these days i'm tryng to calibrate oscope and built a simple L-meter for testing coils.
I found that 7555 generate a square signal not costant, i put a 100nf capacitor from ground and pin 5 but not solved the problem.
Now i post 2 sample photo take from oscope, this is the best i can do, sorry graticula is not visibile.
First one is signal on tx coil 10 vPP, good sinusoidal, if i increase power driver on tr base signal began distorted on top side, second photo.

Bye Max

Distorted signal looks similar to TGS oscillator when the feedback JFet is removed -- But Ivconic says doesn't matter in his tests. Is air depth affected?

-SB

[porkluvr]

I need a break from trying to hack Pspice models from OrCAD into LTspice. grrrrr. Usually pretty easy, but tonight the LM385-2.5 / LM385-1.2 are driving me crazy. Foundation work makes me tired. And it seems to be never-ending.

Not meaning to step on anyone's toes - but I disagree about signal distortion. Maybe on TGSL it doesn't matter so much, but this is not TGSL. Don't assume anything until you have a product that makes you happy, and then you can start testing fudge factors.

The TGSL has no adjustment comparable to the amplitude adjustment on the LOBO, and you don't know how much distortion is acceptable. Power vs discrimination accuracy is what you are trading. You might not gain very much transmitted power compared to the amont of distortion in the phase reference !!! (Looking at Fisher detectors, it seems to me that they take phase reference 50/50 waveforms VERY seriously!)

Waveform distortion on the TGSL (using a Colpitts oscillator) cannot be eliminated, but Tesoro DID attempt to minimize it with the FET amplitude stabilizer. And, it is possible that Tesoro's reason for using the LOBO scheme was -total- (well, almost) elimination of a distorted signal going to the ZCD comparators. Just a thought.

What really bothers me is your saying that the 7555 output is not uniform. I suggest you try another one, maybe that one is defective? Or, check the RC components first. That seems like serious issue. God forbid it's a problem within your o'scope!

[aft_72005]

Hi maxbiri
See pictures, from my golden sabre light , osc out put having distortion ,
I did try to better it with some changes in automatic level control section ,
Contain Fet and zener diode . anyway, I dident important reaction at tgsl
Work.
Best regards.

[maxbiri]

Hi All

I presume that little distorsions are not important but strong distorsions like that in photo give big problems at comparator output, you havent a sigle square pulse but a little serie of fast square pulse that can afct ground cmpesation and disc.
I take same other pictures from o scope, very strange thing happen around 7555!
I change all components aruond 7555, and different 555 type, and put a ceramic multilayer 100 nF capacitor on pin 5 and ground.
Noise at pin 5 is less than 1 mv.
It seem that 20 khz signal is modulate at 10 khz.
Tested oscope, it's ok.
Thinking that problem coming from 7660, that work at 10 khz half F generate from 7555, i remove it but nothing change!
Next step is: remove 4024 and woodo rite!!!
first photo is on 7555's pin 3, second on pin 7.

Bye max

[cordius]

HI,
I read only the last post, check well and make sure that C60 and C63 capacitors near ICL7660 have positive pin on ground.
Excuse my english.

[Unregistered]

Hallo Cordius & Maxbiri.

Think you both are speaking the same language.....?