TESORO GOLDEN SABRE

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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.

[Carl-NC]

Yes, I think you got it.

[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.

[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.

[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.

[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.

[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.

[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]

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.

[dbanner]

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.

[Majster]

Let's simplify it:
The picture shows my layout.
How do I tune the coils with capacitors?

[dbanner]

To raise frequency of TX, add a large capacitor in series with C2. Or maybe change C2 to lower value. That should raise it to beyond the 14.5khz. then you can parallel a cap across the coil to bring it back down as required.

Maybe I said too much, l do not wish to confuse things. Good luck.

[dbanner]

Firstly, tx coil is tuned to 14.5khz and RX coil is tuned to 16.1khz resonance.
However even though it is tuned to 16.1khz, the RX coil will pick up a signal of 14.5khz being transmitted by tx coil. This happens when a metal object is placed in the field and disturbs the null.

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.

[Majster]

Welcome back,

So there's no need to go bending around your coils to tweak inductance.
Fix the tx in place and tune with capacitors. The lock it down so it can't move and forget about it.
Now focus on Rx.
In order to tune Rx, just hook it up the the tx circuit and tune it's resonance for the 1.6khz spread. See?

I tried to use your tips. I thought I understood them. But it doesn't work. My TX coil in TX port (J1.1 and J1.2) has a frequency of 14.2kHz. Attempts to add a capacitor to it only lower the frequency. I used a 1nF capacitor. By no means does the capacitor raise the frequency. The frequency only goes down. This is logical because the theory says f = 1 / (2Pi SQRT (LC)), so if L = const (because I don't bend the coil like you said), and if C = x (initial value, I don't even know which is a capacitor, but I think it's the harmonic mean of C1 and C1, which is close to 20nF), then f (C = x + 1nF) <F (C = x).


I figured I would tune the RX to f = 15.8kHz then (because 14,2 + 1,6 = 15,. But that doesn't work either. The RX coil in the TX port (J1.1 and J1.2) has a frequency of 13.8kHz. Attempts to add a capacitor to it only lower the frequency. By no means do the capacitors raise the frequency.


Don Bowers' documentation shows that after assembling the coils and testing them in the TX port, the frequencies should be 14.5kHz (TX) and 13.95kHz (RX). My values are quite close. They are 14.2kHz and 13.8kHz as I wrote above.


I don't think I understand your tips though. I am really a beginner.


Greetings.

[dbanner]

Here is a little circuit for setting up the null. It is derived from magnum metal locator project. Read the text. Connect to output of Rx preamp.