Fisher F5 antennas

[WM6]

How to explain this statement from Fisher F5 metal detector manual:



despite that (as HAM radio hobbyist) I know what is antenna gain and impedance, it is not clear to me, what this statement mean in relation to F5 metal detector coils?

[Skippy]

Is that an antenna?

[Skippy]

This type of info appears in most of Fisher / Teknetics manuals, and it looks to be there for legal reasons, relating to US and Canadian regulations.
I've never seen the TX coil inductance value for the F5/G2/Greek series etc coil published anywhere. If it's 43 ohms at 7.8KHz, it would imply an inductance of 877 microhenry. This seems reasonable, the F75's coil is 695 uH for comparison. I don't think the 43 Ohm figure refers to it's radio impedance, as it's physical size is massively less than 1 wavelength, so it's impedance would be almost zero.

I don't know about the impedance of the lady in the red dress.

[Qiaozhi]

I don't think this has any direct connection with metal detectors, especially since a metal detector coil is not an antenna.
It's more likely that this is simply a CYA statement.
(CYA = "Cover Your Arse")

I cannot post the US version, as it gets censored automatically.

[WM6]

Thanks both for your opinions.

Follow F5 manual statement, we can conclude that 21dB gain coil/antenna is possible. I wish to see how such coil look like?

From legal point, it is not clear why producer should prohibit MD user with applied antenna gain and impedance - this should be task of state administration.

[Carl-NC]

Industry Canada required statement, nothing else.

[Funfinder]

The radiation power in this case is no antenna-question but how much the detectors circuit provides itself.
Comparable with free walkie-talkies where also a better passive antenna doesn't improves the range very much.
However, perhaps you find a way to amplify the detector like a pirate radio station!

[WM6]

Industry Canada required statement, nothing else.

Thanks Carl.

Hope that Canadian blue collars radiate with less than 3dB at 43 Ohms.