Super TGSL With H Bridge TX Diff RX Quad Sampling

[Davor]

While you are at it, check power consumption, and see how amplitude follows the supply voltage over 6 to 9 V span. Waveform is beyond anything seen on any of the Tx-es on this forum and beyond.

[golfnut]

How do TR2 and Tr9 get their power? I guess you have a decent duty cycle for the 4053 clocking due to the symmetry of the H bridge. Ive been doing some LM386 Tx drives into regular parallel tuned Tx tanks which give a nice 50/50 useful for the 4053 clocking.. Not many of us have microwave office - my lic has expired.. Do you have it as a spice sim? S

[Silver Dollar]

Here's the spice file;

[Silver Dollar]

I ran it up and got the following results;
9v in
8.6 Khz
10.5v P-P
4.1 ma

8v in
8.6 Khz
9.0v P-P
3.6 ma

7v in
8.6 Khz
7.76v P-P
3.1 ma

6v in
8.6 Khz
6.6v P-P
2.6 ma

I couldn't verify the current in the coil but the sim says it's around 150 ma!

[Silver Dollar]

So I'm thinking we have a winner with the new H bridge (H Bridge 3?) and so have been thinking
about the reciever coil. There was a big improvement going from the 100 turn 6.5 mh coil of the
original design to the 170 turn 14.7 mh of the Minelab coil.

So I wonder if going to say 35.6 mh as in the IDX coil and using a .0068 uf cap to get 10229 hz
resonance would improve our signal somewhat?

I bought 2 spools of wire to wind a bifilar coil but I'm not sure I have enough to try many combinations.

You could also go to 45 mh and a .0047uf cap for 10943 hz.

My thought is you can use any inductance that you can get to resonate around 10000 hz but maybe there's
some reason to limit the inductance? I've seen some Whites with RX inductance over 100 mh and some others
with 500 uH.

The big guiding factor seems to be standard cap values and I'm sure cost of the wire comes into
play. We don't have those limitations so maybe we can improve our coils this way?

Oh here is the schematic with the new H bridge drawn in. As always this is a work in progress..

[Silver Dollar]

So I ran some simulations and found out the 35.6 mh coil has the most ampere turns so maybe it's the best?

Tx = 8700 hz

6.5 mh 22 ohms 105 turns with .033uf cap = 10866 hz
Recieved signal - 8V - 15 ma
105 * .015 = 1.575 ampere turns

14.7 mh 34.4 ohms 170 turns with .015uf cap = 10718 hz
Recieved signal - 12V - 10 ma
170 * .01 = 1.7 ampere turns

35.6 mh 70 ohms 280 turns with .0068uf cap = 10229 hz
Recieved signal - 25V - 9 ma
280 * .009 = 2.5 ampere turns

45 mh 120 ohms 320 turns with .0047uf cap = 10943 hz
Recieved signal - 20V - 5 ma
320 * .005 = 1.6 ampere turns

The data for the 14.7 is from a coil I built some of the others are calculated or guessed. The sim might not
be accurate but I was hoping it would show me whether to build a 170 turn or 270 turn bifilar RX coil and it
seems to do that so I'll try it!

[Silver Dollar]

When I tested the H Bridge 3 (AKA New H Bridge) I had forgotten to put the 1 uf cap and trimmer on the board.
So I add them (15 ohms for trimmer) and retested it;

9v in
8.69 Khz
15.3 v P-P
4.65 ma DC
2.87 ma AC ?

8v in
8.69 Khz
13.2 v P-P
4.07 ma DC
2.49 ma AC

7v in
8.69 Khz
11.1 v P-P
3.46 ma DC
2.0 ma AC

6v in
8.69 Khz
9.2 v P-P
2.89 ma DC
1.67 ma AC

[Davor]

Now that's more like it. The previous results were not encouraging. The role of the cap and a trimmer is to provide a sort of folded differential pair with degeneration concentrated to a single trimmer, hence tunable. It is quite unusual, but even in deeper than B class operation you still have pairs of diagonal transistors conducting simultaneously the same current, and the capacitor provides it, thus relieving the emitter resistors of the switching pulses. This results in considerably less current pulses on the supply rail, and the vast majority of current is recycled. So the power consumption is well under 10mA.

I still owe you a phasing network.

[Davor]

Here is my vision of input preamp and a phase shifter. It goes waaaay beyond any other project here. If there was a third channel, we'd have a real beach monster. But even this way it will be a real deal.

[Silver Dollar]

Wow looks good! I plan on doing something with the audio and haven't tried the 4053 mod yet
so you could use the other switch for the salt channel and we can work on the audio afterward.

I'm not really sure what would work the best (for the audio) as volume changes have to be big to
make a difference then you lose deep objects. Some sort of VCO seems best as long as it isn't too
intrusive. Giving the sound some distance by reversing the phase on one side might help. I also
thought about making 3 ranges and using a different tone for each range might sound better
than a vco...

I wound up a new RX last night. I used 280 turns bifilar wound. That should give me 35.6 mh. If it
works out I'll have to wind another TX as the current one is sheilded. Now to make the diff input.

[Silver Dollar]

I am looking at actually implementing the mods and so have renumbered u100 CD40106
to reflect the physical pins I will use. They flow better and can be modded in at the
current 4024 location. The 833 can now be in the LF353 location for both opamps
use in the quad decoding. I had originally planned to use the leftover 358 from the
battery check. Now that one can be used for some sort of audio mod!

[Davor]

There is no real need for LM833, as cheaper and less thirsty choices, like TL072, are quiet enough, and THD is just about the same.
Please note that I did not put designations to the components I added. There are only C's and R's.
In case you decide to open a third channel and go for a real dry/beach mode, a slight modification of the phasing network may be in order.

[Silver Dollar]

Well I still have a LF353 there but might remove it and put the diff input with the TL072.
I'll fix the schematic on the next go around.

I have the sim of the phase network and a picture of min and max GEB and Disc.

It looks great! 270 degrees of control. I probed my Tracker IV and found they are using 270 degrees too...

[Davor]

Actually it is just over 90° for GEB, and just under 180° for Disc, but that covers all the bases.
The third control would be just for a ferrite and it's span would be under 20°, yet it would accommodate for a wider choice of coils, and it would require a separate channel. Without it you still have a functional GEB, and on salty beaches iron gets detected as with a coil in counterphase. Sounds a bit odd, bot works nevertheless. The third channel is not essential for detection on beaches - you get used to the odd sound of iron.

[Silver Dollar]

Ahh I see, I meant 270 degrees of span. I thought to ignore salt we would need to
notch 20 degrees out of the top and bottom of the sine?

I started removing parts off my TGSL and deciding how to add the new ones.
I might leave the TX stuff on the perf board and put all the RX stuff on the TGSL
board. Not sure where to put the 4053....

For those with the Minelab oscillator running at 8700 hz you can just do the
40106 part to get your negative supply back to a higher frequency. It all can
be done on the board at the 4024 socket...