TGSL Tuning & troubleshooting

[simonbaker]

On the coil and the board.

Do you mean you ground both shields (TX shield and RX shield) to the PCB? In other words, resistor R13 (5.1K) and capacitor C6 (.015u) have their connected leads grounded to the PCB ground?

-SB

[dfbowers]

Do you mean you ground both shields (TX shield and RX shield) to the PCB? In other words, resistor R13 (5.1K) and capacitor C6 (.015u) have their connected leads grounded to the PCB ground?

-SB

I guess what I was getting at is:

Do you ground the non-inverting input to the Rx circuit directly on the PCB?

With a USB cable, the non-inverting input to the RX circuit gets grounded ONLY to the coil shield.
Don

[simonbaker]

I guess what I was getting at is:

Do you ground the non-inverting input to the Rx circuit directly on the PCB?

With a USB cable, the non-inverting input to the RX circuit gets grounded ONLY to the coil shield.
Don

Yes, that was my follow-up question too. Maybe Vladimir actually grounds in both places -- I don't really understand the whole grounding business with the RX coil, so I could believe many variations at this point.

-SB

[simonbaker]

USB shields

Q for dfbowers:

In the USB cables you use, is there just one shield, or are pairs of wires individually shielded also?

Regards,

-SB

[dfbowers]

Q for dfbowers:

In the USB cables you use, is there just one shield, or are pairs of wires individually shielded also?

Regards,

-SB

Simon,

The USB-2 cables that I have been using are the same as the sample that I sent you for the unfinished coil. 4 wires inside the foil shield surrounded by a wire mesh with 1 stranded copper wire included in the mesh.

I have used what you discribed (like the Belden-m 8723) on some of my other projects. I built a Volksturm Sm using that cable and it works very well. (It was an old extension cable from Whites).

The cable, coil and shield turns out to be the biggest trick with some of these projects!

Don

[simonbaker]

Simon,

The USB-2 cables that I have been using are the same as the sample that I sent you for the unfinished coil. 4 wires inside the foil shield surrounded by a wire mesh with 1 stranded copper wire included in the mesh.

I have used what you discribed (like the Belden-m 8723) on some of my other projects. I built a Volksturm Sm using that cable and it works very well. (It was an old extension cable from Whites).

The cable, coil and shield turns out to be the biggest trick with some of these projects!

Don

Ok, thanks. I bought three different brands of 6 ft. USB cables to compare.

The cheapest ($3.99 IdotConnect) has a very thin foil shield with a copper shield wire (stranded) and four internal wires.

The next most expensive, ($4.97 Green Products) has a good loosely braided shield around a good foil shield, with a copper shield wire (stranded), and four internal wires.

The more expensive ($7.99 Belkin) has a good braided shield with what may be a silver shield wire (stranded) and more spiral wrapped foil shield, and four internal wires. It appears that the green and white pair may be twisted.

I did not buy the very expensive cables (around $25), but some may advertise separate shields on the pairs.

All three cables looked usable, but the cheapest connectors did not fit nearly as snugly as the others, so I favor the middle cheapest.

Theoretically, I would think separately shielded pairs would be desirable, but dfbowers gets good results with single shield, so... there it is.

-SB

[Vladimir]

Do you mean you ground both shields (TX shield and RX shield) to the PCB? In other words, resistor R13 (5.1K) and capacitor C6 (.015u) have their connected leads grounded to the PCB ground?

-SB

Yes, see post # 188, there are changes in the Rx, but it is the essence of the Tx and Rx connected to GND and Shild

[simonbaker]

Yes, see post # 188, there are changes in the Rx, but it is the essence of the Tx and Rx connected to GND and Shild

Sorry, I'm still not clear - is that ground at J2 pin 2 referring to the coil shield or the PCB ground?

Regards,

-SB

[Vladimir]

Sorry, I'm still not clear - is that ground at J2 pin 2 referring to the coil shield or the PCB ground?

Regards,

-SB

This was clearly.
J2 pin 2 is connected with the coil shield and the PCB ground.
Regards

[simonbaker]

This was clearly.
J2 pin 2 is connected with the coil shield and the PCB ground.
Regards

Hi Vladimir:

I think what dfbowers was asking is: do you also ground the cable shields together at the PCB? (see green line in attached photo).

-SB

[dfbowers]

TGSL shielding and grounding..

Question for the experts:

While we are on the subject of shielding and grounding, I happened to notice a couple of things.

* Early on in the TGSL threads, Ivconic was experimenting with OO coils and he was NOT grounding one end of the Rx wires to the sheilds OR to the PCB ground.

* In some of my current observations, I noticed that wet vegetation does disturb the operation of the TGLS somewhat.. Dry land, not at all..

Just as a quick experiment, I have a coil laying on my bench (Shielded) , yet to be cast in resin. If I simply take a few blades of grass and wet them, and then touch the coils, the TGSL is much more sensitive to touch if either of the Rx wires are grounded to the sheild.. much LESS sensitive to touch if left in a true differential mode. Which would lead me to ask.. why ground either wire on the Rx circuit? The Rx circuit should "see" the shield but not be part of it!! Would anyone agree?

Why did Ivconic change grounding schemes midway through the main thread?

Anyway, at the expense if making another complete coil, my next will be in a true differential mode, and I should be able to ground one end of the Rx circuit at anytime.. just like the configuration using audio cables.

Be back in a few day when the resin hardens in my next coil..
Don

[simonbaker]

Question for the experts:

While we are on the subject of shielding and grounding, I happened to notice a couple of things.

* Early on in the TGSL threads, Ivconic was experimenting with OO coils and he was NOT grounding one end of the Rx wires to the sheilds OR to the PCB ground.

* In some of my current observations, I noticed that wet vegetation does disturb the operation of the TGLS somewhat.. Dry land, not at all..

Just as a quick experiment, I have a coil laying on my bench (Shielded) , yet to be cast in resin. If I simply take a few blades of grass and wet them, and then touch the coils, the TGSL is much more sensitive to touch if either of the Rx wires are grounded to the sheild.. much LESS sensitive to touch if left in a true differential mode. Which would lead me to ask.. why ground either wire on the Rx circuit? The Rx circuit should "see" the shield but not be part of it!! Would anyone agree?

Why did Ivconic change grounding schemes midway through the main thread?

Anyway, at the expense if making another complete coil, my next will be in a true differential mode, and I should be able to ground one end of the Rx circuit at anytime.. just like the configuration using audio cables.

Be back in a few day when the resin hardens in my next coil..
Don

I agree, same question - what is the logic of the cable grounding? Maybe it just works! It would also seem to depend on kind of cable - Vladimirs audio cables, vs USB 4 wires in shield, vs. Belden 4 wires with pairs shielded separately. Maybe in one case better to ground, other not? Intuitively, I would think the Belden 4 wires, shielded in pairs, with no RX grounding at all would be least noise. Maybe not though.

I tried also on bench many times ungrounding the RX coil - on scope you see much bigger common mode noise when ungrounded I remember, but output of LF353 pretty much the same whether grounded or not (from a null signal standpoint -- can't really see the tiny differential noise, which may be quite different and is the whole point here).

I wonder if the common mode noise could get very large and overload the common mode range -- doesn't seem that likely, but maybe?

How does Tesoro do it?

-SB

[nakky]

I noticed that wet vegetation does disturb the operation of the TGLS somewhat.. Dry land, not at all..


I have the same problem.
A wet sponge give the same problem,a lot of falses.
But when I acros the front of the coil with my forearm (ulna) it give a good response,like a coin.
Who can tell me, what the problem is.
Thanks.

Grt Nakky

[dfbowers]

I noticed that wet vegetation does disturb the operation of the TGLS somewhat.. Dry land, not at all..


I have the same problem.
A wet sponge give the same problem,a lot of falses.
But when I acros the front of the coil with my forearm (ulna) it give a good response,like a coin.
Who can tell me, what the problem is.
Thanks.

Grt Nakky

Looking back through the threads now, I get the impression that Ivconic arrived at his conclusion through trial and error. It would be interesting to see how Tesoro does it, but we cannot compare a concentric directly with the DD design unless they offered one for the TGS.
Don

[Vladimir]

Hi Vladimir:

I think what dfbowers was asking is: do you also ground the cable shields together at the PCB? (see green line in attached photo).

-SB

-YES- they are at GND