Volksturm SM + GEB

[kt315]

oh mama mia... i see my project is live. NICE!

http://www.radioingener.ru/metallois...lksturm-smgeb/

[usta]

Yes, that is correct! So, if your RX coil is around 6.2mH then your capacitor for resonance should be 61nF. That would be the best place to start and then either go larger or smaller. http://www.whatcircuits.com/lc-reson...cy-calculator/

Don

thanks a lot Mr Don, this is great help for me!
other thing i can't open the link since it have JS/Agent.NCA trojan!!
thanks a lot again

[dfbowers]

thank you, this is what i was looking for!!
i don't have LC meter but when i used coil calculator it gave me about 6.2 mH.
so i must first don't null my coils, then i must change caps to see maximum resonanse, ( now my tune is good) , then i must overlappe my coils litle by litle to see minimum resonance at signal(so this is fine null and fine tune too), tel me know if i am wrong!
thanks in advance

Yes, that is correct! So, if your RX coil is around 6.2mH then your capacitor for resonance should be 61nF. That would be the best place to start and then either go larger or smaller. http://www.whatcircuits.com/lc-reson...cy-calculator/

Don

[usta]

1. Yes, you should see an 8170Hz signal no matter what.. It should be almost nothing on pin 1 of the LF353 when nulled though.

2. Signal will be maximum at resonance but at the same time minimum when nulled. (So look for a maximum while adjusting phasing but a minimum while nulling).

What is the value of L for your RX coil????

Don

thank you, this is what i was looking for!!
i don't have LC meter but when i used coil calculator it gave me about 6.2 mH.
so i must first don't null my coils, then i must change caps to see maximum resonanse, ( now my tune is good) , then i must overlappe my coils litle by litle to see minimum resonance at signal(so this is fine null and fine tune too), tel me know if i am wrong!
thanks in advance

[dfbowers]

ok, 1-so when coil is null, i must see this frequency or not?
2-as i understand correctly when the ferequency amplitude is maximum (or minium?!!) with for example 100 nf capacitor, my tune is good, true?
please answer to this two question with yes or no for question 1, and maximum or minimum and a few more explain for question 2.
thanks in advance

1. Yes, you should see an 8170Hz signal no matter what.. It should be almost nothing on pin 1 of the LF353 when nulled though.

2. Signal will be maximum at resonance but at the same time minimum when nulled. (So look for a maximum while adjusting phasing but a minimum while nulling).

What is the value of L for your RX coil????

Don

[usta]

You will not see a frequency change at the receiver when you change the RX tuning capacitor, only a change in amplitude. If your TX frequency is 8170Hz, then this is what you will get at the receiver ... nothing different.

ok, 1-so when coil is null, i must see this frequency or not?
2-as i understand correctly when the ferequency amplitude is maximum (or minium?!!) with for example 100 nf capacitor, my tune is good, true?
please answer to this two question with yes or no for question 1, and maximum or minimum and a few more explain for question 2.
thanks in advance

[Qiaozhi]

Don,
my version is volksturm sm+geb (with tl081)
yes, when i separating my coils a few i can see 8170 Hz, but it is same for example with 47 nf cap or 150nf capacitor!
please tell me know i must see the frequency at pin 1 of u1a at good null or no?
my Rx coil is 90 turn , .25mm copper wire and each coil when is round is 25cm diameter.

You will not see a frequency change at the receiver when you change the RX tuning capacitor, only a change in amplitude. If your TX frequency is 8170Hz, then this is what you will get at the receiver ... nothing different.

[usta]

Oh, sorry.. I meant look at pin 1. It's just the amplified and inverted version of what you see on pin 3. You should see something on pin 1 just by separating your coils a little
I should ask, what version did you build?
If you cannot reject ferrite, that would suggest that your phasing is off as well.

Can you tell me the value of your RX coil? Do you have a way to measure? If we know that, then we can make sure that you are "close" to begin with.

Don

Don,
my version is volksturm sm+geb (with tl081)
yes, when i separating my coils a few i can see 8170 Hz, but it is same for example with 47 nf cap or 150nf capacitor!
please tell me know i must see the frequency at pin 1 of u1a at good null or no?
my Rx coil is 90 turn , .25mm copper wire and each coil when is round is 25cm diameter.

[dfbowers]

Mr Don, thank you for reply
i think my null is good, when i test U1a pin 1, and when i close the coil overlappe litle by litle, i can see in my oscope that at one point the frequency show line is close to liner, i think there is my fine null, true?
but there (pin 3 of u1a) is not any frequency, i test with 10nf cap to 150 nf, nothing!!
sensitivity is good, more than 25 cm for 1inch coin, but my problem is that i can't reject ferrite at all!
i am amateur in electronic!! if i know from where i can see my Rx frequency, i think i can tune my coil fine!
i hope you help me in this matter!
thanks in advance

Oh, sorry.. I meant look at pin 1. It's just the amplified and inverted version of what you see on pin 3. You should see something on pin 1 just by separating your coils a little
I should ask, what version did you build?
If you cannot reject ferrite, that would suggest that your phasing is off as well.

Can you tell me the value of your RX coil? Do you have a way to measure? If we know that, then we can make sure that you are "close" to begin with.

Don

[usta]

Hi, your english is good.

Check pin 3 in U1a on the LF353. If your coils are slightly out of null you will basically see the RX signal, same frequency as the TX coil. If not tuned, the Volksturm will "work" but have poor sensitivity. You must put a capacitor across the RX coil (JP2 1 & 2) to get the RX coil in resonance with the TX frequency. If you have an idea if the inductance value of the RX coil you can then calculate the value of the capacitor needed. That should be a good starting point. Then add or subtract capacitors to find the highest RX signal.

Don

Mr Don, thank you for reply
i think my null is good, when i test U1a pin 1, and when i close the coil overlappe litle by litle, i can see in my oscope that at one point the frequency show line is close to liner, i think there is my fine null, true?
but there (pin 3 of u1a) is not any frequency, i test with 10nf cap to 150 nf, nothing!!
sensitivity is good, more than 25 cm for 1inch coin, but my problem is that i can't reject ferrite at all!
i am amateur in electronic!! if i know from where i can see my Rx frequency, i think i can tune my coil fine!
i hope you help me in this matter!
thanks in advance

[dfbowers]

Hi Mr dfbowers,
yesterday i built the volksturm sm+Geb, it work and can detect metals but it seem the coil is not tuned, i have pc oscope and frequency meter, can you please say to me that from where i must see my RX frequency? when i test Q3 emmiter(that go to TX) i can see 8170HZ, but when i test pin 3 of lf353( Rx) there was not any frequency, i wonder to know if i do this wrong and if yes from where i can see the RX frequency to tune the coil fine?
excusme for bad english

Hi, your english is good.

Check pin 3 in U1a on the LF353. If your coils are slightly out of null you will basically see the RX signal, same frequency as the TX coil. If not tuned, the Volksturm will "work" but have poor sensitivity. You must put a capacitor across the RX coil (JP2 1 & 2) to get the RX coil in resonance with the TX frequency. If you have an idea if the inductance value of the RX coil you can then calculate the value of the capacitor needed. That should be a good starting point. Then add or subtract capacitors to find the highest RX signal.

Don

[usta]

I guess we should open a new thread for this since the last one was off topic.
Anyway, I have uploaded a short demonstration:

http://www.youtube.com/watch?v=5qLD5rkzEFU

This one is with the VCO option (with the 8k2 resistor and a jumper).
Don

Hi Mr dfbowers,
yesterday i built the volksturm sm+Geb, it work and can detect metals but it seem the coil is not tuned, i have pc oscope and frequency meter, can you please say to me that from where i must see my RX frequency? when i test Q3 emmiter(that go to TX) i can see 8170HZ, but when i test pin 3 of lf353( Rx) there was not any frequency, i wonder to know if i do this wrong and if yes from where i can see the RX frequency to tune the coil fine?
excusme for bad english

[M.T]

hi everybody
plzz parts liste

[dfbowers]

The Volksturm can be set up to Ground balance or Discriminate, but not both at the same time. It goes deep if ground balanced properly but then I find myself digging tiny nails and bits of iron . I may experiment with it configured as a "two box" if I can find some time.

[yhl]

The metal detectors can distinguish metal it? Be discrimination?