Serbian "Most Wanted"

[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

[eduardo1979]

Is an NPN transistor Q7. BC547, 546, 548, 237, 238, 236, etc.

[jlsilicon]

Can Q7 (BC237) be replaced with BC547 or BC546 or BC337 ?

[jlsilicon]

Suggestion,
The cd4053 (A) Pin should be tied to High or Low. Else, you risk leavig a Cmos pin as unstable, that will possibly/probably cause a free oscillation which (even with the Output pin disconnected) also probably cause NOISE in the rest of the circuit- like feedback back into the Vcc and Gnd. I saw this occur in another MD project.

The same for the Unused Lf347 OpAmp +/- Input Pins.

[walkman]

how so? : D