Howdy.
I think you may mean VLF or "very low frequency". Most metal detectors run anywhere from about 3 kHz to about 20 kHz. But most VLF detectors only run on one frequency, whatever that frequency may be.
I am no tech head, but the problem with salt water beaches is that the wet sand and the surf is highly mineralized, which tends to overload the single frequency VLF detector when you go from dry sand to wet, leading to constant false signaling.
Two kinds of detectors were developed to respond to this problem.
There is the pulse induction (PI) detector which is absolutely unaffected by ground mineralization and gives tremendous depth (targets 12" deep are not unusual). Unfortunately, a PI detector offers absolutely no discrimination whatsoever and you will therefore dig trash and treasure and you'll never know what it is until you scoop it out. Some advanced PI users say they learn certain differences between good and bad targets based on the tone, but that does take a lot of practice.
There is also the dual frequency detector, which will run on two alternating frequencies, usually one very low (say 3 kHz) and one very high (like 15 kHz). Like I said, I not a tech person, but those alternating frequencies help keep the machine balanced. But you often have to re-balance the detector if you go from dry sand to wet sand/surf. Once balanced, the falsing signaling drops off tremendously.
But we aren't finished yet.
Not long ago there was another technological step made by Minelab when they came out with the multi-frequency detector. It apparently alternates between dozens of frequencies which keep the machine very stable and you don't have to re-balance the detector ever. Downside is, those machines aren't cheap either.
You will notice more and more detectors being sold today run at 10 kHz and higher. Part of the reason for that is that everyone has gold fever right now, given the extraordinary price of gold. Higher kHz detectors are more sensitive to gold so people are flocking to it. The problem i have found is that it can be more unstable and isn't as sensitive to silver. And regardless, you have to run your discrimination at a minimum to find the gold.
This obssession over kHz can be a little disingenuous, because its not the frequency of the detector that makes it sensitive to gold as much as it is how the detector process that frequency and its signals. You don't necessarily need a higher frequency detector to nail gold, unless you're talking about tiny nuggets.
One last thing i have noticed. I do not know why this is true, but the lower your frequency, the better the detector seems to handle wet salt sand. I ran a Detectorpro Wader for awhile (less than 3 kHz) and while it wasn't a depth monster, I had no problem with falsing on the wet sand or in the surf. I'm not saying run out and buy a low frequency machine, but it is worth looking into some more.
Wow. Sorry for the brain dump. Hope it helps.
