TGSL Experiments

[Jerry]

Hi Simon:

Here is the setup.

Pic #1 shows the scope probe connected to J2-2 and ground.
the other probe off to the right is for the tx signal and is connected right at the coil cable input connector.

Pic #2 is just a closer view

Pic #3 is of the scope and digital voltmeter setup.

Pic #4 is a closeup of the BNC adapter I am using.

Pic #5 is a very poor camera angle showing the wiring at the coil. The White and green wire are not shorted and are the connected to the RX. The white wire is grounded to the coil shields. Tx is grounded at the PCB.

Note: This is not a good setup for doing air testing. Most anything you hook to the detector is like a little antenna. So I remove when doing a serious air test.

Hope this sheds some light on what I was trying to say.

Jerry

p.s. After taking these pictures, I did a quick air test and it was hitting solid at 30 cm on a two Euro coin with the null setting and voltage shown in the picture.

[simonbaker]

Hi Simon:

Here is the setup.

Pic #1 shows the scope probe connected to J2-2 and ground.
the other probe off to the right is for the tx signal and is connected right at the coil cable input connector.

Pic #2 is just a closer view

Pic #3 is of the scope and digital voltmeter setup.

Pic #4 is a closeup of the BNC adapter I am using.

Pic #5 is a very poor camera angle showing the wiring at the coil. The White and green wire are not shorted and are the connected to the RX. The white wire is grounded to the coil shields. Tx is grounded at the PCB.

Note: This is not a good setup for doing air testing. Most anything you hook to the detector is like a little antenna. So I remove when doing a serious air test.

Hope this sheds some light on what I was trying to say.

Jerry

p.s. After taking these pictures, I did a quick air test and it was hitting solid at 30 cm on a two Euro coin with the null setting and voltage shown in the picture.

I think I get it now!

My only thought is as before, that measuring one side of differential input doesn't necessarily measure the relevant phase. However, in this case because RX coil is grounded in search head, it gives you a reasonable idea (unless a big bad common-mode voltage is running around).

The actual signal that is "detected" of course is the output pin 7 of LF353 -- which is not exactly same as RX coil phase at inputs, but that is what Synchronous Detector sees and works on.

I would "die" for your and dfbowers' Casablanca target fan and a noise-free basement to test in...

Regards,

-SB

[Jerry]

Here is a pic of my workshop building taken from the deck at the house.

Jerry

[simonbaker]

Here is a pic of my workshop building taken from the deck at the house.

Jerry

You're cruel!

Looks like heaven to me -- even some fall foliage happening.

Now we expect great things of course!

Cheers,

-SB

[simonbaker]

it's the noise

Temperature hit around 114 deg here today.

We lost power to a blackout.

Didn't know what to do. Then it hit me... no noise!!!!!!

I got so excited I almost browned my trou - except it wasn't a brown-out... so I fired up my TGSLs for some air tests (of course couldn't use scope).

Interesting stuff.

With my "insane" PCB ( 1 Hz center frequency) and my "alien" coil, I could get 1 Euro at about 43 cm. It detected my cell phone at about 68 cm. Crazy beast though.

dfbowers PCB and my "alien" coil (in resin) got about 30 to 34 cm with 1 Euro. Gain at max.

My standard PCB with my "alien" coil could get about same, 30 to 34 cm. If I really tweaked the sensitivity pot to just below chatter, I could get a crappy chirp 36 to 40 cm. But not really serious detection. However, I don't really like my beep as much as dfbowers PCB. His has softer edges and smoother.

I tried dfbowers PCB, my alien coil (with crossover connector), with sensitivity at minimum. Air depth with 1 Euro about 15 cm.

Same test with my PCB, I get about 20 cm. That probably means that his thresholds have different offset than mine, and also I can tune my PCB for my coil, which is not optimal for his PCB.

Then I tried dfbowers coil with his PCB. Air depth with 1 Euro easily to 30 - 34 cm. Some detection almost out to 40 cm.

My PCB with dfbowers coil -- not so good! It just didn't sound good, beep too short, break up, depth in the 20 to 25 cm range. I finally did some oscillator trimming and C6 trimming, careful sensitivity setting, reduced my GB pot, and got some better depth, high 20's. But just not a good fit for some reason.

My PCB also has a tendency to get a double beep somewhere in the middle of the range. I hadn't found that before. I'm quite sure it is not the "backward RX wiring" problem. Something changed recently? I think jumper-grounding the speaker ground to the battery ground helped a little. It could be the buss partly. Bad headphone jack? It is flaky somewhat. I may try the bypass capacitors also.

Well, it was a pleasure while it lasted. Lights are back on now. Will I ever know why dfbowers coil and my PCB don't work well????

-SB

P.S. usually I have Euro attached to stick. This time I used my hand. Could my hand have assisted the depth a little? Possibly. I tried hand only, and no detection, but still need to mention it.

[simonbaker]

Filter experiment

Qiaozhi had an idea which we should test but my setup is not too good. I think dfbowers and Jerry are probably best equipped as far as I know, but anyone with low noise environment is invited.

Basically it is a tweak to one of the filter sections which raises the gain a little. Also slightly raises bandpass.

Since this falls under the general area of "filter tweaking", I'm putting in my own request also. I've already done my "insane" variation which I haven't reported on well due to time constraints, but initial tests indicate it is too far out to really interest anyone seriously, I think.

So here are two mods to try if anyone is willing.

1. Qiaozhi's mod: change C20 and C23 from .022 uF to .01 uF.

2. SB's mod: change C14, C17 from 4.7 uF to 10 uF (or back-to-back 20 uF electrolytics).
change R31, R29 from 470k to 1 Meg.
change C18, C21 from .47 uF to 1 uF.


I'll try to experment too, but will take me a while to setup and test.

The test is to see how the detection depth and overall detection quality is.

-SB

[Jerry]

Hi Simon:

Would raising the bandpass freq of the filters make any change in how higher conductive targets like U.S. Quarter dollars are detected? From the start my TGSL gets 4 - 5 cm better air test readings than a quarter will.

Jerry

[simonbaker]

Hi Simon:

Would raising the bandpass freq of the filters make any change in how higher conductive targets like U.S. Quarter dollars are detected? From the start my TGSL gets 4 - 5 cm better air test readings than a quarter will.

Jerry

I would think targets that make a sharper pulse might come through a little better. So I would think higher bandpass freq would favor smaller, shallower targets. I suspect it's not like a PI detector where conductivity affects the pulse -- this is such low frequency that it's probably more a function of size, shape, and depth relative to the search coil -- in other words the shape of the detection signal envelope.

Just my guess -- but proof is in the pudding! You're one of the goto guys for such tests.

I'm going to take my "insane" PCB and put sockets for the caps and some resistors so I can really try some different filter shapes, and cross my fingers that the sockets aren't too flaky and make a mess.

Regards,

-SB

[Jerry]

Hi Simon:

All of the active devices on my TGSL are socketed. Even the transistors.
I have not had a single issue with the sockets. I think Ivconic's circuit changes and board layout are very forgiving. I have had good luck with it so far.

This particular board was my test project, I am going to make another for field use once I have my coil potted and everything tested outside in the real world.

Jerry

[simonbaker]

Hi Simon:

All of the active devices on my TGSL are socketed. Even the transistors.
I have not had a single issue with the sockets. I think Ivconic's circuit changes and board layout are very forgiving. I have had good luck with it so far.

This particular board was my test project, I am going to make another for field use once I have my coil potted and everything tested outside in the real world.

Jerry

I can make anything flaky!

Look forward to how your production model goes.

Regards,

-SB

(how's the foliage?)

[Jerry]

The fall color is about at it's peak right now. We are going camping for the weekend. Will pick this up again next week.

Jerry

[lunamay]

hi jerry

do you know this "magic" voltage of coils when balancing? You said something that it's not necesery to make a almos 0 voltage. maybe you know something that can help. i have coils that have 6.5mH and 6.06mH from wire that ivonic adviced and my deep is poor. how about yours?


best regards

[lunamay]

hi simon

i have a idea! maybe you should mesure every value of voltage and capacintance etc from dfbower's pcb and then copy it to yours:P

seriously maybe that's not so bad idea.. maybe some mesurements..symply voltages and ewerything that can be mesure by multimeter.. could give you(and maybe me:P) som answers about poor working

best regards

[lunamay]

another thing about freaquency..what is your freaquency on pcb(when signal is going to coil) maybe that's our problem
coil is working in other freaq than pcb.. or maybe i don't understand this problem


real best regards

[simonbaker]

The fall color is about at it's peak right now. We are going camping for the weekend. Will pick this up again next week.

Jerry

If you're willing to say, where are you located approximately? What elevation?

Regards,

-SB