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There is much confusion - some of it deliberate - over how many frequencies a detector actually
uses, and whether multiple frequencies are truly better than a single frequency. What defi nes a
multi-frequency detector? What do multiple frequencies really do for depth and discrimination?
A multi-frequency detector is defi ned as one that simultaneously—or, in automated sequence—
transmits, receives, and processes more than one frequency. Some detectors have the ability to operate
at one of several selectable frequencies, but they still are single frequency detectors because during op-
eration they can only transmit and process a single frequency. The same is true of detectors that have a
control to slightly vary their operating frequency to minimize interference; even though they have the abil-
ity to operate at many (slightly) different frequencies, they are fundamentally single frequency designs.
Currently, all multi-frequency hobby detectors run their multiple frequencies simultaneously as opposed
to sequentially; they are all characterized by having multiple processing channels in the receive circuitry.
Therefore, a 2-frequency detector will have two processing channels.
Spectra
V3
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has three independent
processing channels; it is a true 3-frequency detector.
This all sounds easy, so where is the confusion? It turns out that (currently) all multi-frequency
detectors create a transmit signal that is composed of digital waveforms which are designed to produce
peak energies at the desired frequencies. As a side-effect, these digital waveforms also produce unde-
sired harmonic frequencies. Lots and lots of harmonic frequencies, 10’s or even 100’s of them. These
harmonics have no useful energy and are not part of the signal processing. So while we can claim to
transmit many, many frequencies, we cannot claim to process or use them. Therefore, we could easily
claim the
Spectra
V3
i
transmits 17 frequencies, or 28, or 39, or 55—we could get plain silly with this. And
such a claim would be true, technically speaking, but since all those extra frequencies are not actually
used, it would be misleading to make such a claim. White’s chooses, instead, to claim the number of
frequencies we are actually using and processing. It may not sound as impressive as a 55-frequency
detector, but it’s honest and accurate.
Pulse Induction (PI) detectors also utilize a digital (pulse) transmit waveform, so they transmit a
tremendous number of harmonic frequencies as well. So is it fair to include pulse induction as a multi-
frequency technique? Not really, because PI detectors process in the time domain, not the frequency
domain. So even though they use broad-band signals, they are not frequency-based detectors at all.
Calling them “multi-frequency” is simply another attempt to confuse the consumer.
Once we get beyond the marketing hype, the real question is: What does multi-frequency do
for depth and discrimination? The truth is, any time a detector is simultaneously transmitting more than
one frequency, the transmit energy must be divided amongst the frequencies. Therefore, a single fre-
quency detector can usually squeeze out slightly more depth than a multi-frequency design at that certain
frequency. But this is an advantage only at one frequency, which tends to favor only a narrow range of
targets.
3 Freqencies “why not 28!” ...
3 Freqencies “why not 28!” ...
