Detector for sea beaches UK

[Koala]

Should have mentioned it the silverdogs IDX with manual GB. Can balance over saltwater or very close some places slightly positive. Results very good in the right conditions and very poor in others.

Quick question. At some places I was having multi target at different depths with brass and iron near the surface. I was running in disc mode and the surface targets were overloading the detector making pinpointing impossible. Normaly I just raise the coil a bit but this did not work due to the multi targets. Would I have been better cranking the threshold/sens or both down to pick of the surface target first.

[golfnut]

Hi Davor,

"IDX is not much of a detector for beaches , first because it has a fixed GB"

Not true it has a GEB pot and and you see the GEB gating move on scope..



What is the phase of wet Salt sand?? Is it on the side of Fe and soil/ground OR is it on the other side where non Fe lives??


Koala.

2 targets is a bit of a pain, commercial machines may not deal with this greatly. I would dig a fair bit out and spread it out over a couple of square feet. This way you may pick off one target.

The concentric is probably better at beach work as they have a smaller cone shaped feild and pick through litter better than a DD. They can give better iron reject.

The DD is a good sweeper for the cleaner sites. I use a NEL Hunter currently on inland feilds and it was a worthwhile investment.



If you dont have a probe get a garrett - they dont have much range - but they will lett you visualise where the iron is in the hole ok.



With my IDX I have been extremely lucky to get permission on a previously undiscovered site which showed crop outlines for only one year. Approx 170 yards rectangle with lots of joined squares within.

I took 3 small roman and a piece of bronze from furnace activity within an hour or so. Coinage from 325 to 350AD.

not tried wet sand with mine - too nervous about the copper coil dissolving with seawater!!

Been looking close to a 13th century moated manor house, with a nice jetton etc - hoping for some nice finds before the year closes out.

S

S

[Davor]

What is the phase of wet Salt sand?? Is it on the side of Fe and soil/ground OR is it on the other side where non Fe lives??

It is almost entirely on the FE side, but with white/loess sands, and limestone it goes straight to the ~90 degree area in between Fe and non-Fe. This transition may be very abrupt when searching the very coast line, so there is no easy solution.
In my case there are terra rossa terrains next to the shore line, and a simple GB control simply can't turn that far to compensate. Point is that in any moment there is only a single angle at which you have a proper GB, but at the shore line the change from one solution to the next is very sharp. That's why I thought of analogue multiplication of 2 GB channels in order to get both GB solutions simultaneously. It would be a complication (a big one), and that's precisely where simple PI machines are at big advantage (being deaf to both ferrites and salts)

[golfnut]

"Point is that in any moment there is only a single angle at which you have a proper GB,"

I strongly agree.


If you had uniform wet sand or used in the surf, then a relatively simple geb gating shift should be the answer.

If simple single cap single R phase advance circuits were not enough then we could delay with a longer gate shift to early side of the next pulse.

S

[Davor]

Angles that any meaningful GB can have span within ~90°, beginning from Rx to Tx phase shift. Very few rigs have this Rx to Tx phase shift compensated in a front end (e.g. Verator has), and it's a pity, as it would make switching from one coil to the next much easier, and between different coils you'd keep the same GB and discrimination solution.

As GB partly compensates for a Rx to Tx phase shift, it's adjustment span is reduced, so beach hunting surely suffers. I made some plans on a kind of an universal solution, but so far did not put it to action.

[Waikiki_Sweep]

It is practically useless to search salt water with VLF detectors because salt water makes signals equal to aluminum foil (as well as small gold).
Waves, ponds, wet sand dunes will create strong false signals on VLF or you have to decrease sensitivity too much.
Good depth on salt water beach you can have only with PI detector or multifrequency VLF like Fisher CZ series or Minelab Excalibur II or CTX 3030 (Even this one with $2,400 price requires to lower sensitivity adjustment in salt water :-)))) )


Unfortunately nobody offers any VLF multifrequency schematic here to build.

[Davor]

That might change. But when it does the discrimination-less PI domination on the beaches will not die out with the change.

Current marketplace suggests that there are only multi frequency VLF and PI competing in this field, so it is hardly going to change.
Trouble with all the beaches is that there is not enough difference between a pulltab and a piece of jewellery to make the trouble of making the VLF rigs beachworthy. Unless you want to use the same rig everywhere (which is my objective).

I might extend my LF project objectives so that it encompasses a 2 frequency universal GB ... thing. It is far closer to practical realisation than many other approaches, and it would make for an all terrain rig, but I doubt it would make lots of followers. Extending a GB range for a common VLF seem a clever thing to do if you want an existing VLF to be your only tool. Otherwise a PI hype is too strong right now, and it is by all means easier to have a separate tool for beaches etc.

So just decide on your objectives and see if a single device, or multiple devices are your thing. It is all doable.

[Koala]

I don't mind have two detectors. Different tools for different jobs. Seems the most interesting parts of the beach are the parts that the IDX fails. That's the collection of pebbles and the edge of wave eroded shingle banks.

The top of the beach the IDX and DD seem like a good combination. Picks up coins even though the beach has already searched.

Which would be better on UK beaches

Baracuda Legend PCB
Hammerhead I Rev D

or is there nothing between them. I understand the Hammerhead is more adjustable and the Baracuda if built to original spec has a washed out iron sound. But which works the most stable on UK beaches.

[Davor]

I'd say it is up to one's taste, so try finding a fellow detectorist with these detectors to borrow for a trial. Odd things make difference.

[Koala]

Went to the beach again yesterday. Found a small crucifix a press sheet brass gear and some modern money. Need to bite the bullet now as there were areas even around the high tide mark that I could not detect. Large black rocks (looks like granite) everywhere each give a strong nice beep. So ordered a Baracuda PCB from Silverdog. Did dig up a heavy rock that look like iron slag. Fetched it home. Hit it with a hammer the outer crumbled away and there was three small copper nuggets inside.

[Davor]

Any photos of it?

[Koala]

Any photos of it?

The nuggets were in a piece of slag that was hard and slightly magnetic. It could be filed and gave of sparks when touched to a grinder. but crushed to powder when hit with a hammer.

[Koala]

This is the offending black rock. Gives very strong signal. Can't disc out. Equally strong signal in all metal mode. Is hard and none magnetic.



dug this out from about 11"

Ground balance has no effect.

Looks like it been dumped in one area for coastal erosion most of its in chunks about 6" square but bits are starting to beak off

[golfnut]

It may be furnance slag of some sort, hard to say.

I saw an episode of time team once where a guy had a hand held gun thing and he pointed it at a rock in his hand and it read out the elements in the rock !!! Just like star trek.
Thats what we need here...


The center lump in the other photo looks a bit gold like rather than copper?

S

[Koala]

They are very heavy. All came out of the same sample. I could try and find the specific weight but my scales only go to 0.1 gram and I think at that size the error would be too great. They all had a black glaze around them that I scrapped off. Yes the middle one is very gold in colour the photo in artificial light does not do it justice. I've just scratched through the surface with my thumb nail.

Saw that episode of time team. Bet they bought one of there own for geophis to use. Was not the same when Mick Aston and his colourful jumpers left. Very nice and knowledgeable bloke. Shame he no longer with us.