TGSL Tuning & troubleshooting

[turtlebowl]

4.7 uF Bi-Polar for sale

Hey folks.....I know this may be a bit out of bounds but if you guysthink so I'll delete this post.
In the states the 4.7 NP cap is difficult to find cheaply. Not so in Britain for some reason.
At least thats been my experience.
I stumbbled on some in the fee bay site a few months ago that were 20 for $5 with free shipping. I thought I had nothing to loose so I just ordered them. I was pleasantly surprised to find them in y mailbox with in a week even though the seller was from China!
I have posted here over enough years for you guys to know that I am in no way associated with the seller. But I am providing a link to the guys ebay store in the hopes someone else has the same good luck I had with this seller.
I opted to pay 3-4 dollars for the guys expedited shipping instead of his free shipping that he offered.
Only you can decide but here is the link.
If I am out of line let me know and I'll remove the post.

http://www.ebay.com/itm/20pcs-Panasonic-BP-Bi-Polar-Capacitors-4-7uF-63V-/220771333144?pt=LH_DefaultDomain_0&hash=item3366ff3418

[Jerry]

Anyone tell me where to put the meter to measure your nulling?

Steve

You can use terminal 1 & 2 of the coil connector but Pin 1 of U1a is also a good place because it is isolated from the coil. Just remember that the op amp has a gain of about 47 so be mindful of that when calculating the null voltage.

Jerry

[simonbaker]

Anyone tell me where to put the meter to measure your nulling?

Steve

Is there a doctor who can answer that...?












getting carried away, time to shut off computer...

[simonbaker]

coils and loops are low impedance devices and are always described in terms of magnetism and H field. E fields (voltage) are rarely discussed with coils.

Which is ironic because it's actually the E field that moves the current...

When you provide a coupling mechanism (a current coupling mechanism - ie eddy currents in a target) the result is you have upset the fine tuning - nulling of your Tx Rx loops and a tiny nett current flows in the Rx coil - this current flowing in the Rx coil generates a small output voltage - which is amplified by the op amp.

You the get your trowel out

And after digging a few holes, some of us throw the towel in...

[golfnut]

Anyone tell me where to put the meter to measure your nulling?

Steve

[golfnut]

coils and loops are low impedance devices and are always described in terms of magnetism and H field. E fields (voltage) are rarely discussed with coils.


When you provide a coupling mechanism (a current coupling mechanism - ie eddy currents in a target) the result is you have upset the fine tuning - nulling of your Tx Rx loops and a tiny nett current flows in the Rx coil - this current flowing in the Rx coil generates a small output voltage - which is amplified by the op amp.

You the get your trowel out

[simonbaker]

OH!!!

May one inquire which country? SA or where?

Regards

Andy

Boring old La La land (southern california USA)

[simonbaker]

Hi Simon, the non magnetic portion is screend away to ground isnt it. The E field part.

We are leaving a gap in the sheild so we dont hold in the magetic H field component - thats what I was told.

RF can be mystifying

steve

Hi steve -

When I refer to non-magnetic "null component", I'm more thinking about something like capacitive coupling in the cable, or even magnetic coupling that is too far away from the search head to be affected by targets (ground, ferrite, etc.).

I believe you are referring to the components of a propagating electromagnetic wave, but that is something else. It's not possible to screen away one part and leave the other.

The gap in the shields, in my way of looking at it, is mainly to prevent the shields from developing a strong induced current from the TX magnetic field, particularly the TX shield, since the RX shield is "balanced" along with the RX coil.

A strong current in the shields, besides likely wasting energy, would probably throw off our phase relationships needed in the detection and discrimination circuitry. (I wonder if it might be possible to redesign the circuit so it would work with a continuous shield.)

I won't speculate more because, I agree, emf can be mystifying, and all the effects and purposes of the shields are not something I understand. Hope to understand it better some day.

Regards,

-SB

[der_fisherman]

I live about 10 hours from London -- by jet. But I'll dream about the those pints you kindly offer, though they rightfully belong to all the experts here I learn from!

Hair of the dog!

-SB

OH!!!

May one inquire which country? SA or where?

Regards

Andy

[simonbaker]

Dear SB
I thank you kind Sir for the full explanation that was also easy to understand! Could not have been better put!!

I am also sure you helped several others at the same time.

Regards

Andy

PS. The next time I am in the UK, you have earned a few pints from me as well!! Are you somewhere in the south of the UK? (Hopefully!)

It will have to be a Pub as I always have my Weimaraner with me.....

I live about 10 hours from London -- by jet. But I'll dream about the those pints you kindly offer, though they rightfully belong to all the experts here I learn from!

Hair of the dog!

-SB

[golfnut]

HI Silverdog I just got hold of some off fleabay.

S

[golfnut]

non magnetic component

Hi Simon, the non magnetic portion is screend away to ground isnt it. The E field part.

We are leaving a gap in the sheild so we dont hold in the magetic H field component - thats what I was told.

RF can be mystifying

steve

[der_fisherman]

Hi SilverDog,

I have decided to get it working as it is, then later change out the caps and see what the difference is.......I have already ordered the caps in question.

Thanks for your reply.

Regards

Andy

[der_fisherman]

Wrong Caps in IGSL

I would just go ahead an put in non-polarized ones, either a 4.7 uF (and jumper the empty space) or two 10 uF non-polarized in series as per the PCB layout. People have been very successful with the back-to-back 10 uF polarized -- but I personally would use non-polarized until I learn more about the long-term effects of back-to-back polarized.

I will guess that using the "wrong" capacitor (two 4.7 uF in series) would make an MD that would be superior for smaller shallow targets in conjunction with a smaller coil, but it would not respond as well to deeper targets in conjunction with a larger coil.

If you look at another TGSL modification by eduardo and produced by silverdog, you will see those capacitors are changed in the other direction -- he uses 11 uF for that capacitor, and uses a 1 Meg resistor for the LM358 feedback resistor -- this makes an even slower and higher gain response than the IGSL -- maybe better for large coils and deeper targets.

We have not really proved this in the field, although dfbowers has built and reported on eduardo's modification http://www.geotech1.com/forums/showp...postcount=4716 .

So choice of filter characteristics is not a cut-and-dried subject. But for the IGSL, I would definitely use the 4.7 uF or 5 uF value, not 2.35 uF.

Regards,

-SB

Dear SB
I thank you kind Sir for the full explanation that was also easy to understand! Could not have been better put!!

I am also sure you helped several others at the same time.

Regards

Andy

PS. The next time I am in the UK, you have earned a few pints from me as well!! Are you somewhere in the south of the UK? (Hopefully!)

It will have to be a Pub as I always have my Weimaraner with me.....

[dfbowers]

I can't comment on this issue as my knowledge of electronics is basic

I have just replaced the 4.7uF on my IGSL with 10uF, I can't notice any difference with my test targets, although this is an air test

I will from now on supply 10uF caps for these positions - if anyone who has purchased an IGSL kit wants a replacement - PM me

Silverdog

Andy, I wouldn't worry too much about the differences. Awareness is probably the most important thing. Also, that's just my opinion and I have not had anyone verify those characteristics. Coils and cable will aways be different as well.

For all the trouble you go through to put the kits together, I would recommend just building as is. Pretty minor differences in the big scheme of things!!