Metal Detector Search Coil - Antenna Or... ?

[Tye]

Steve,

Thats great! I'm glad to see manufacturing people like Carl on here... big benefit.

Ive never read anything you've said about it....and I think I've said pretty much what I wanted....I will add that my guess about the RF Carl is talking about surpressing is not the stuff coming down the transmission line as that's all there is....but leakage of electronics and/transmission line leakage .... due to various anomalies (slight mismatches etc.) .... I don't feel the need to mention the details of my experience with the world of electromagnetic theory and practice but it does span  about 4 decades ... not that it really matters ....

Thanks for the great resource Steve....

Cheers..Tye

[FeO2digger]

Wow thanks for the push to look even a bit deeper guys, great links Steve to the resources Carl has provided. Will be reading over much as I love to better understand what makes all "tick"!

[Geotech]

1 hour ago, MikePfeiffer said:

I was mentally building more into the circuit than you are describing, However, I do not fully understand. Why would you not impedance match and get all the signal strength you can. What about the TX coil. Please don't tell me it is just 50 turns of wire attached to a 3904 transistor.

Impedance matching is done on RF systems where circuits are difficult to design with low/high impedances, so they are normally designed around 50 or 200 ohm impedances. At sub-MHz, it's easy to design around opamps which don't need impedance matching. For the RX coil, the incoming magnetic field induces a voltage on the coil, so all we need to do is slap it on a non-inverting opamp. For the TX coil, yeah, you can stick it on a 3904. But usually it's resonated with a capacitor at the desired frequency. This creates a sinusoid, plus recycles energy. Not for impedance matching.

[MikePfeiffer]

I used to work on radar and impedance was critical. I went to collage in the early 70s and got thrown into management. Been retired for many years. I have forgotten  a lot. Thanks for being patient. I will read your book again. Just got to find where my wife hide it.

[Geotech]

Yes, in radar impedance matching is critical. There are no opamps to make life easy!

[MikePfeiffer]

Months ago I asked about using a SFO for TX. Now I understand that the coils not being antenna will not work.