whites rx coils and tuning?

[jim p.]

hey everyone, I built a coil for my whites 6000 and it pretty much works
but the rx coil must be off because it does id right. On a scope, my tx
coil seems to be right because I get a nice waveform and it's the right
frequency and amplitude, but I'm having trouble getting the receive coil
to work just right. If I pass a nickel in front of the coil, it reads
down near iron, if I pass a quarter in front of the coil it reads down
near nickel. playing around with the number of turns on the recv coil
moves this point around some but i still cant get it right. how do you
guys figure out the right number of turns for recieve coils? Do you just
go by what hte manufacture did in their coils? How about if you wanted a
bigger coil, thats what I did, I made an 18 inch coil for relic hunting
(18 inch tx coil) and my rec'v coil is 12 inches roughly. I think I must
have too many turns or not enough because Im having to add a lot of
capacitance to get it to do what I have gotten so far and I think that
makes the q of the coil bad huh?

is there a formula for figuring out the right size/inductnace of the
recv coil? Does anyone know what inductance I should have before
capacitance adding for a 6000?

thanks carl, really nice forum you have here.

[Robert Hoolko]

I don't think the receive coil is tuned. You should be able to get the right ID with no capacitor on the receive winding. If the ID is way off you may have the receive phase reversed.

As for the number of turns, just put enough turns so the amplitude of the received signal matches the amplitude from the factory coil for a coin sized target near the coil.

Robert

[Chris]

Hi Jim

Check the link below out. There you will find a brief description how to make and setup (adjust) a concentric search coil (RX,TX). If you can not read Russian than you should make use of the Russian web translator at "http://www.translate.ru".

Chris



coil assembling & adjustment (http://mikaml.narod.ru/ring.htm)

[jim p]

now the problem is that my detectors (whites 6000 and idx) both make a ringing noise when I plug in this coil - not too loud, but enough to notice. It works and has decent depth, and even ids pretty much correctly, but the ringing noise is scaring me. I used a 5:1 (rx:tx) turns ratio and the rx coil isn't tuned like the tx coil is. any ideas? tks!

[Robert Hoolko]

You might give more detailed information about the ringing. Is it coming from the speaker, or the coil, or from somewhere in the box other than the speaker? Is the ringing always constant or does it depend on what is near the coil?

I don't have a clue what it is, but if you give enough details someone may recognize what it is.

If it is coming from inside the box I would be a bit worried.

Robert

[jim p]

hi robert, thanks for the ideas - the noise is a high-frequency (maybe 15khz) constant noise, coming from the control box. It worries me too, but I think it's in the receive circuit, since the noise isn't there if just the tx coil is connected. I wonder if it's some sort of resonance ringing?

[Carl]

cap is mechanically resonating. This is easy to find, by just poking your finger around on caps until you dampen the one that's ringing. Make sure you aren't statically charged first.

You don't want to let this go on, because it can eventually break a component. Once you find the component, perhaps a dab of glue will change its mass enough to stop the vibration.

- Carl