To Notch or Not To Notch?

rdavison

Senior Member
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Feb 16, 2007
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San Jose, Ca
I wanted to get some clarification on notching. If I notch out certain signals, is it done in the transmit signal or the receive signal? If it's done in the transmit will this decrease my sensitivity or depth? Being concerned it does work on the transmit side is there MD units that transmit fully and filter out (sound) the notching on the receive side only? Any Info would surely be appreciated. Rick :?:
 
I would say its on the recieve signal.I can notch out signals on my minelab but if I look at the meter it still reads a signal just no sound.
 
My Garrett does the same thing. When running in a preset mode, or in All Metal with any range manually notched out, the display will register "silent targets" in the notched out ranges.
 
rdavison said:
I wanted to get some clarification on notching. If I notch out certain signals, is it done in the transmit signal or the receive signal? If it's done in the transmit will this decrease my sensitivity or depth? Being concerned it does work on the transmit side is there MD units that transmit fully and filter out (sound) the notching on the receive side only? Any Info would surely be appreciated. Rick :?:

Hi Rick,

You asked several questions that deserve separate answers as they are not related in th emanner you suspect.

The notching is a Discriminate function. As such, it is an integral part of the receive side. It has no effect on the transmit signal.

Now to the second part of your question. Because the discrimination circuit, notch or otherwise, is not "perfect", targets in the vicinity of the range being discriminated, will have some sensitivity loss (ie. loss of depth). This, I'm afraid, is unavoidable.

Lastly, most all detectors are designed such that the transmit power is constant, not variable. This is because it would be too expensive to make otherwise for various technical reasons. What is changed is the receiver side sensitivity. In a top end detector, you may have a separate pre-amp gain and amplifier gain. In lower end units, the pre-amp gain is fixed by design.

In most modern designs, the discrimination setting affetcs the sound produced and not the display.

I hope that answers your questions.
 
Notch is a filter in the receiving circuitry. Having another filter to pass the signal through lowers the amplitude of the signal and reduces your sensativity to fainter(deeper) targets.
 
Iron(disc) filters also reduce the amplitude or the signal and that is why you get more depth in all-metal mode. The more you increase your disc., the more signal is lost having to pass through the filter. High end detectors can be compensated for this by increasing pre-amp gain which amplifies the received signal.
 
Thanks, It seems I'm going to be looking for a new detector that has a pre-amp gain then. Thanks Guys, appreciate info. :!:
 
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