Tuned coils

Re: Tuned coils

Thanks I did Guess you really never forget Morse Code either Glad I retained something from back then

WA2EVR if you have any old CallSign Books from the '70's you'll find me there

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HH

Beachcomber

Re: Tuned coils

.... .- ...- . .- -. .. -.-. . -.. .- -.--

N2SN also G4FEB

Re: Tuned coils

Makes sense to a degree. I keep thinking back to my Amateur Radio days when we wanted everything to be tuned from the transmitter tank circuit to the antenna as well as the front end of the receiver. Matching the tuning of the antenna to the transmitter allowed for the most efficient transfer of power insuring the as much of the tranmitter power was actually being radiated and not being fed back into the tranmitter which caused additional heat. We always strove for an SWR of as close to 1 to 1 as possible.

Since the coil on the metal detector is in essence it's radiating antenna I would have thought tuning the coil to the same frequency as the transmitter would be important if you wanted to make the most of the limited transmit power. I can see your point about not tuning the receive winding or tuning it off frequency.

Thanks for your response Dave!!!!

HH

Beachcomber

PS It's funny how the more things change the more they stay the same. Years ago I used to use Morse Code and SSB to communicate with people around the world. Today I use a computer and the Internet to talk with people around the world Have a Great Day!!!!

Re: Tuned coils

Here is the explanation: A tuned circuit made from a coil and a capacitor is an excellent way to get rid of noise. The capacitors you see on Whites, Tesoro and other detectors do indeed tune the coil but NOT to resonance. The coils are commonly tuned lower in frequency than the transmitters frequency although they could also be tuned higher. The effect is that the receive signal is much lower in amplitude than if the coil were tuned to the transmit frequency. The reason that this is done is to help get rid of the noise that the coil is picking up. As the coil is not resonant to the transmitters frequency there is no threat of phase drift and other instability problems. If you try to use a receive coil which is tuned to resonance you will have drifting discrimination and ground balance settings to the extent that the detector will be unusable. Hope this clears things up, Dave. * * *

Re: Tuned coils

I was wondering the same thing but not because of anything that Dave had said but just an impression that I have based on things I have read about the latest detector designs. Years ago and I am talking about the 70's and 80's I know the coils were tuned and some even had capacitors in the coils themselves to help achieve the tuning that they wanted. But recently I have gotten the impression that they are not so specifically tuned and are much more broad banded than they used to be. Hopefully someone who knows for sure one way or the other will post and help clear this up.

HH

Beachcomber

Dave E. mentioned below that tuning the coil on a VLF is generally a bad idea. However, isn't this fairly standard practice amongst manufacturers? I know that Tesoro puts a coil cap on the main board.

- Carl