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[walkman]

My SMW 555 TX-470nf - 7.7Khz- 8.6 Vac/ RX- 1nf - 8.2 Khz

I can't understand
you smw 555 tx balance 470nf rx balance 1nf is that so?

also amplitude 7,7khz

but 8,6vac and 8,2 khz

how and where to set?

[emoxristov]

By increasing the frequency is not possible to make a primer and becomes unstable with false tone.7-8 Khz works best . amplitude is greater than 10 volts is not stable.

[Davor]

This version of oscillator is way better than the typical oscillators in popular VLF builds, but there is also a catch... you can't use it with any coil. The coil for this Tx must float, so it must not have any of the ends connected to a shield.

In case you build your own coil it is not a problem at all. The op amp takes care that the conduction is precisely 50:50 so the 2nd harmonic will be greatly suppressed, and purity of signal will depend mostly on how the supply voltage is pure.

The same job would be performed even better with a real balanced oscillator, as you have to have a Tx coil floating anyway. The advantage of a balanced mode operation is that a net E-field of such coil in operation is zero, so capacitive feedback from Tx to Rx coils is off the table and better balance is achieved. With single ended operation a net E-field of a coil is half the voltage across the Tx coil, and capacitive feedback limits the depth of achievable balance.

[emoxristov]

My SMW 555 TX-470nf - 7.7Khz- 8.6 Vac/ RX- 1nf - 8.2 Khz

[jlsilicon]

Thanks Davor.
I am working on a Version of this Board myself.
And, I want to figure out the advantages of the different Revs and Mods to test.

* Is this version (that I linked) have a better or worse Transmitter with the OpAmp
- than the (2) Transistors Transmitter Design Rev used on the Boards in this forum ?

I want to try adding in some improvements myself,
but of course, I want to understand the design, test it, and have a working version first.

I am not an analog engineer - so its slow for me to understand the design.

[walkman]

hi;
finish

[Davor]

There are several other solutions that are nice to see here other than the speed switch.

So what does the switch do ... it sets the low pass filtering action of the first stage channel amplifiers. With 100n LPF corner frequency is set at 15Hz and with the rest of the filtering time constants you have overall band pass filtering response with maximum set at about 10Hz. With lower values of capacitors the bandpass maximum shifts slightly up, allowing somewhat faster sweeping speeds, but at a cost of introducing some more noise (negligible).

There is only one problem with this approach that was overlooked, but easily cured. The anti-chatter circuitry around IC6B has LPF corner frequency set also at 15Hz, but in order to actually benefit from faster earlier stages C23 should be reduced to 33n.

[jlsilicon]

I there any explanation for the 'Speed Rotate Switch' on this Version Schematic ?

http://www.hobbielektronika.hu/forum/getfile.php?id=198041

I might guess its functionality. But I see no forum notes on this Mod.

Does anybody have any knowlege into the Switch Usage, Why-was-it-added, and its Advantages/Disadvantages ?

[walkman]

what coils value tx and rx for 32cm.


What should be the value of the voltage amplitude?.


And other value?.


Waiting for a detailed description.

[Davor]

It could be due to several things. I'd start with coil balance. In video it seem you have some commercial coil. Did you check the signal level prior to 4053? Just because it is all potted doesn't mean you can't improve the coil balance - it can always be done with a small piece of ferrite and a small piece of foil.

[emoxristov]

I use 347 have maximum amplitude in the receiving coil but no depth of detection. Where is problema.10mm. Coin of not more than 20 cm. 60 cm air.Nad no detection of even large objects.

[Davor]

Changing R22 R23 is safe from the point of filter corner frequencies, but R25 and R27 must be adjusted together with C14 and C16 to make sense.
Channel filters are a bit touchy for making such adjustments. Safe way is observing each branch function and making sure frequency response of a branch is maintained. You could for example reduce R25 and R27, but simultaneously increase C14 and C16. This particular change may prove a bit tricky because 1uF comes at "normal" dimensions, while 2uF or larger tend to be huge in comparison. Option "B" is reverting to electrolytes, preferably bipolar.

There is another issue that is usually overlooked: noise. Using LF347 or TL074 gives advantage over the original LM324

[emoxristov]

changed-R22 R33-51k R25 R27-4k7 but not stable
Somewhere there is a mistake there is not enough depth

[Davor]

It is too neat

[emoxristov]

My SMW

http://www.youtube.com/watch?v=RjB8MgSwuSI&feature=youtu.be

http://prikachi.com/images.php?images/754/6159754Y.jpg