TESORO GOLDEN SABRE

[dbanner]

Next step is to work out the actual inductance of your Rx coil so you can select a capacitor value for tuning to 16.1khz.
I found that a resonance calculator on Android phone or PC helped me with this sort of thing.

[Majster]

Put a 470nF capacitor in series with C2 (you'll have to desolder one leg of C2 from PCB and join a 470nF in series. Connect the tx coil.
That will raise tx frequency to 14.5khz.

OK, adding 470nF in series with 22nF gives a total of 21nF, so we're lowering only a little C, so we're increasing only a little f. It's logical.
Suppose this actually drives the TX coil to 14.5kHz. Propably yes.
Later in the same TX port I will tune the RX coil, right? So you wrote. Will I have to solder then some additional capacitors to the PCB together with C1 or C2 to tune RX to 14.5 + 1.6 = 16.1kHz? This does not seem wise to me. It seems to me that I will rather solder a capacitor in series with the RX coil. Do I think right? If yes, isn't it better to solder something C in series to TX?
Tomorrow I will take care of it, currently it's 10pm in my country, so I have to sleep now. I'll be there in ~ 18h.
For now

[dbanner]

Firstly, I calculated 470nF not by guess. You said your TX frequency is 14.2khz, given the values for C1 and C2 of 220nF and 22nF, your TX coil inductance works out to 6.28mH.

So for getting 6.28mH to oscillate at 14.5khz you need 19.18nF tank capacitance. This is obtained by adding a 470nF capacitor in series with C2.

[dbanner]

Now for Rx coil tuning.

Connect Rx coil to tx circuit ( unmodified without the additional 470nF capacitor).

You can now measure it's frequency.

Now it's inductance can be calculated. Take 20nF (effective tank capacitance of colpitts oscillator) and whatever frequency you measured and plug into formula to solve for inductance. I use online calculator.

So now you know the exact inductance of the RX coil. So now just calculate what value capacitor you need to put in parallel to tune for 16.1khz
I use online calculator for this.

Reconnect Rx coil to its proper place (receiver circuit) and use nearest standard value capacitor to what you calculated. You should try to get as close to the calculated value of capacitor. Now remember you can't measure 16.1khz at Rx coil when it's connected to Rx preamp. You can only measure frequency of received signal from the TX.

Next step is null the coils and adjust the ground balance trimmer.

[Carl-NC]

The tx circuit is a colpitts oscillator, so there are 2 capacitors, which makes up the total tank capacitance. So I think it is C1xC2/C1+C2.

Correct.

It seems to me that I will rather solder a capacitor in series with the RX coil. Do I think right? If yes, isn't it better to solder something C in series to TX?

I have not looked at the TGSL design in a while so it may be possible to put a add a series cap to the RX coil. However, that forms a capacitive divider that will reduce the signal level. It's better to start off with a smaller cap and a too-high frequency, then add some parallel cap to bring it down to what you want.

Also, you cannot put a cap in series with the TX coil, the Colpitts requires a DC path through the coil.

[waltr]

Whether the TX oscillates at 14.5kHz or 14.2kHz does NOT matter.
Only thing that matters is the RX resonance is about 1.6kHz higher than the TX resonance......

If you wish to tune with the caps and the Frequency is TOO LOW, then replace the cap in circuit with one smaller. Now you can put another cap in parallel to increase the C and decrease the f.

[Majster]

Welcome back,

Teraz do strojenia cewki Rx.

Podłączyć cewkę Rx do obwodu tx (bez modyfikacji bez dodatkowego kondensatora 470nF).

Możesz teraz zmierzyć jego częstotliwość.

Teraz można obliczyć indukcyjność. Weź 20nF (efektywna pojemność zbiornika oscylatora Colpittsa) i dowolną zmierzoną częstotliwość i podłącz do wzoru, aby obliczyć indukcyjność. Korzystam z kalkulatora internetowego.

Więc teraz znasz dokładną indukcyjność cewki RX. Więc teraz po prostu oblicz, jaką wartość kondensatora musisz umieścić r?wnolegle, aby dostroić się do 16,1 kHz.
Używam do tego kalkulatora online.

Podłącz cewkę Rx do właściwego miejsca (obw?d odbiornika) i użyj kondensatora o standardowej wartości najbliższego obliczonej. Powinieneś spr?bować zbliżyć się do obliczonej wartości kondensatora. Teraz pamiętaj, że nie możesz zmierzyć 16,1 kHz na cewce Rx, gdy jest ona podłączona do przedwzmacniacza Rx. Możesz zmierzyć tylko częstotliwość odbieranego sygnału z TX.

Następnym krokiem jest wyzerowanie cewek i wyregulowanie trymera do gruntu.

I think I understand it now, but it took the Colpitts generator formula.
F = 1 / (2Pi * sqrt (L ((C1 * C2) / C1 + C2)))
I understand that from it you calculated the C2 correction and it is 470nF in series with C2 which gives a combined capacitance C2' = 21nF. It is true. The capacity corrected in this way corresponds to the frequency of 14.5kHz. I verified this value in online calculator.
I soldered 470nF as you said, and measured the TX frequency. It is f = 14.45kHz, but it is easy to change it with a very slight curve/bendof the TX coil and then f (TX) = 14.50kHz. This is really a very slight bend of the coil, not more than 0.5 - 1 cm. It's probably acceptable.
I didn't take anything out of the PCB, 470nF is still there. Then I connected the RX coil to the TX port (J1.1 and J1.2) and measured the frequency. It is f (RX) = 14.06kHz. Based on this data, I calculated the inductance of the RX coil. It is L (RX) = 6.68mH.
I guess it's still easy. I need to calculate C6 because RX coil will not work in TX port, but in RX port, so it will be a normal oscillator with frequency f = 1 / (2Pi * sqrt (L*C6)), and this frequency should be 16.1kHz. From here I calculated that C6 should be 14.63nF. If so, I will have to desolder C6 (currently 15nF) and insert 2 capacitors in parallel there, which will give a total of 14.63nF. The closest sum will be 10nF + 4.7nF.
Did I calculate it correctly? Do you think I understand it correctly?
Greetings.

[Carl-NC]

Yes, I think you got it.

[dbanner]

10nF +4.7nF=14.7nF

Or

560nF capacitor in series with C6 but maybe it's better 10+4.7 because they are both small physical size and will fit nicely on PCB.

[dbanner]

Welcome back,



I think I understand it now, but it took the Colpitts generator formula.
F = 1 / (2Pi * sqrt (L ((C1 * C2) / C1 + C2)))
I understand that from it you calculated the C2 correction and it is 470nF in series with C2 which gives a combined capacitance C2' = 21nF. It is true. The capacity corrected in this way corresponds to the frequency of 14.5kHz. I verified this value in online calculator.
I soldered 470nF as you said, and measured the TX frequency. It is f = 14.45kHz, but it is easy to change it with a very slight curve/bendof the TX coil and then f (TX) = 14.50kHz. This is really a very slight bend of the coil, not more than 0.5 - 1 cm. It's probably acceptable.
I didn't take anything out of the PCB, 470nF is still there. Then I connected the RX coil to the TX port (J1.1 and J1.2) and measured the frequency. It is f (RX) = 14.06kHz. Based on this data, I calculated the inductance of the RX coil. It is L (RX) = 6.68mH.
I guess it's still easy. I need to calculate C6 because RX coil will not work in TX port, but in RX port, so it will be a normal oscillator with frequency f = 1 / (2Pi * sqrt (L*C6)), and this frequency should be 16.1kHz. From here I calculated that C6 should be 14.63nF. If so, I will have to desolder C6 (currently 15nF) and insert 2 capacitors in parallel there, which will give a total of 14.63nF. The closest sum will be 10nF + 4.7nF.
Did I calculate it correctly? Do you think I understand it correctly?
Greetings.

Yes.

[Majster]

Welcome back,
I did this: I desoldered C6 (it was 15nF) and put 2 capacitors 10nF + 4.7nF = 14.7nF in parallel there. I connected the TX and RX coils to dedicated ports. I connected the mV AC multimeter to ground and the IC101 / 7 pin. I turned on the power. I moved the coils to get the minimum value on the multimeter. Unfortunately, the lowest value that can be obtained is about 0.5V AC, which is still 100 times too much. I connected the osciloscope electrodes to Visual Analyzer, and to the TX and RX ports. I recorded the waveforms from both coils (attachment file). Unable to get flat RX wave. Do you have any idea what I could do now?
Greetings.

[dbanner]

Measure the RX residual voltage across the RX coil, before the preamp. This is true residual value of voltage.

It is not possible, I don't think, to get absolutely zero volts. There is always some small voltage even at deepest null.

But for tgsl, you are aiming for slightly offset from deepest null.

You want approximately 20 degrees phase difference between the tx waveform and RX waveform as your balance point. This is the point at which everything works correct in the circuit for ground balance trimmer and discrimination.
At 20 degrees you will have slight voltage on Rx coil greater than deepest null.

[Majster]

Welcome back,
I did as you advised: I turned on the power, set the coils so that the voltage value between ground and IC101 / 7 was minimal. I was able to get 0.48V AC. I turned it off and on again. Without moving the coils, I re-measured the voltage between ground and IC101 / 7, I got a repeatable result, i.e. 0.48V AC. So the position of the coils is rather stable. Then I turned off, unhooked the multimeter electrodes and turned it on again. Then I measured the AC on the TX connector and got 6.16V AC, I measured the AC on the RX connector and got 5-11mV AC, not very stable but not higher than 11mV. My multimeter is APPA 305, so it shows frequency during these measurements. It is 14.14kHz on the TX connector and 0 on the RX connector. I assume that the voltage on RX is too small for the meter to pick up the frequency correctly, besides, I saw an oscillogram showing two sinus after subtracting the dc, so that doesn't bother me.
Are the AC voltage values that I have read promising? What should I do now?
When you write about angles, I don't really understand what's going on, but I know it has to do with the TX and RX sinus waveforms. When they are not completely in phase, it means that they are moving away from each other by some angle (ahead or lagging behind) and that it depends on the independent frequencies TX and RX which differ by 1.6kHz. But I do not know exactly where or how to measure this angle, or how to regulate it. I think, that only by changing the frequency of the coils, which in turn is regulated roughly with capacitors, and more precisely with the final positioning and bending of the coils. Do I think right?


BDW I have already started the second TGSL PCB. I assumed that if I did something wrong on the first PCB, the second PCB would be comparative. I have already soldered the IC sockets and bridges. I read in the documentation that a few elements can be replaced, for example LM308 to TL071, and pnp transistors 2N2907 to BC557, npn 2N2222 to BC547. Are any other substitutions possible?
Greetings.

[waltr]

The Phase is the time difference of when the peak (or Zero crossing) is of the RX relative to the TX wave forms.
14.5kHz has a period of 68.9micro-seconds.
20 degrees divided by 360 degrees = 0.055 of a rotation. Multiply by period equals 3.8 microsecond time difference between TX and RX.

Look at the TGSL 101.pdf again, Scope picture #4 on page 6. Top trace is TX, bottom trace is RX. Note that the RX peaks are slightly (20degree) after the TX peaks. Also note the scope vertical scale and then read the peak-peak voltage in the picture.

[Majster]

Welcome back,
Thanks for the clarification, you're really good at this, really. I'm just learning and I can't judge my oscillogram like that, but I guess it's not bad. Besides, it is not a real oscilloscope, but a computer adapter. I can't expect her to work better.
But let me tell you something: with my PCB, I visited a friend who has an old Russian oscilloscope, still analog (I can't find what model it was on the network) and not fully functional (no electrodes and problems with switches). And when I connected the PCB to it, for the TX waveform it showed exactly the same sine wave distortion as in the Don Bowers documentation.
What do you think - can I already think about GB and discrimination at this stage?
Greetings.