Question to all those who build VLF detectors concerning recovery speed and such...

[Steve in MS]

I have been wondering if some of you know why some detectors have a slow recovery speed and some fast. I am referring to the discriminate mode and I realize that either the use of 4 or 2 filters designs come into play on this but I suppose there is more to it than that. Does the disc mode on them have some form of auto tune circuit also? If someone knew how all this works out then it appears to me one could take a fast recovery detector and tweek it and make it even faster, that could make a detector do even better in trashy areas. I don't know anything about electronics but was wondering if anyone has made any thought about it.
Regards,
Steve

[Max]

I have been wondering if some of you know why some detectors have a slow recovery speed and some fast. I am referring to the discriminate mode and I realize that either the use of 4 or 2 filters designs come into play on this but I suppose there is more to it than that. Does the disc mode on them have some form of auto tune circuit also? If someone knew how all this works out then it appears to me one could take a fast recovery detector and tweek it and make it even faster, that could make a detector do even better in trashy areas. I don't know anything about electronics but was wondering if anyone has made any thought about it.
Regards,
Steve

Hi,
much depends on how integrators are realized. If there are big capacitance values then you have a slow response, otherwise a faster one.

Not only: if there is an active auto-tune feedback the response time is then related to the block response... so a slower block will give you a slower response.

Often both , great caps and great time constant autotune blocks are used in VLFs 8and other designs too) cause they improve stability of detector... but you'll pay that with slower response and also less sensitivity to far targets (cause far targets give just weak and "fast" transients on the rx side).

Then, if you want to improve your detectors response you have to study schematic and then change values of some components... so find a good compromise between stability and sensitivity to small and far things (with faster response).

Best regards,
Max

[Steve in MS]

Thanks Max...

I know most of you are building from schematics so I was just wondering about the possibilities. I figured there was some type of autotuning going on or resetting. I mostly lurk here on these forums, didn't know if I would get a response.
Regards,
Steve

[Carl-NC]

As Max mentioned, it is a trade-off between selectivity and sensitivity. Faster recovery will improve selectivity, but it also means weak short signals get filtered out. Perhaps what we need are two separate channels, one fast & one deep.

- Carl

[geshi]

Probably the result recovery speed will be as fast as the slower channel, so in this case we will gain 0

[diamondjim]

I've seen this question brought up plenty of times in the past...guys worry about missing stuff because of slow recovery times. But in truth there are far easier ways to deal with the issue than fiddle around inside the box.

In a trashy area you have two options: dig everything or go to a small coil. Don't worry, your big coil isn't going to "see" through the trash anyways...you're only missing what you couldn't have found anyways. Depending on the value of the site, there are a few places I dig everything merely to get it out of the way to get to the deeper layers or remove square nails to get a clear picture of other targets. Don't have a small coil? Roll your sens knob way, way back...till a penny air tests at 4 inches...this reduces the number of junk signals the machine has to recover from. I know that's a tough concept to accept sometimes...but if it makes the difference between getting a few good things or getting nothing at all, why not?

In less trashy areas of high value, I hit the site from three different angles with my stock 9" coil and sens run wide open...east to west, north to south, then at 45 degrees. Many times I've been able to eek out a few more keepers that were near a junk target by changing the direction of my search pattern.

If your concern is missing stuff due to slow recovery times, try the above methods first, if your intent is to learn electronics and refine detector technology then welcome to the ranks of the technically insane.