Hammer Head with 3 foot coil

[Rob in KS]

I finally have it finished enough to take it out for a test drive. I live on an old farmstead, so there are a LOT of targets in the soil. Most of them are iron. Many of them small; pulltabs, bits of wire, nails. I tied the coil between 2 trees and swung a couple of targets.

Beer can 2 feet
shovel 4 feet
55 gal drum lid 5 feet (18" dia)

I think I could do better, but I had to use what I had on hand. The coil came from multiconductor shielded cable. Its about 396uH 9 or so turns. Non VCO, passive pulldown. Subject to change.

Here are the changes I made to the HH
R3 - 1K
R4 - 680
R45 - 100K
C24 - 20nF
C8 - .1uF
C17,C18 .47uF

Here are the ranges.
Freq 100 - 266Hz
Main Pulse - 52 - 375uS
main delay - 24 - 160 uS
Sec Delay - 95 - 850uS
Sec Pulse width - 5 - 55uS

[Rob in KS]

The pictures didn't make it

[Rob in KS]

On my first test drive, I didn't find any large targets. As I walked, I could hear small targets go by. I didn't find anything large but I got into a field of "smaller" targets. I could hear that it was a bunch of small targets

[Rob in KS]

Oops I did it again

[Carl-NC]

Looks good!

Any particular reason for placing the coil above the wheels, instead of just below the axles?

[Rob in KS]

I know I'm losing a foot by having the coil so high. I'm looking at this wheat field. They use "no-till" farming so the stubble is still standing. It goes pretty well in tall grass. I didn't glue the wheel posts, so I can make shorted ones.

Any suggestions are welcome.

[1843]

Hammerhead works excellent with small coils. My HH detects a bear can at 50-60cm with 4" coil!!!
Coil is 500uH and pulse width 260us . I have adjusted frequency at 400-500Hz; because when I set it to 100Hz, SP sound is not good...

Regards

[Rob in KS]

This one was running a 4" coil when I built it. Its a handy size for testing. Its a better quality coil and I got about what you did on a beer can. My main delay is probably too long for aluminum when I changed it for the big coil.

[1843]

Try to add 3-4 turns on your coil... 9 turns is little...

[Reg]

Hi Rob,

I am curious as to why you wanted such a large coil? At first, I suspected you might want to check the plowed fields for meteorites since that is becoming quite the thing, especially since there has been a few valuable ones found in Kansas. If this is the case, don't forget to check along the fence lines. Over the years, large rocks are found by farmers and ultimately removed from the fields. Generally, they are just tossed at the edge of the field, which is quite often at a fence line. A very small percentage of these rocks are meteorites.

Remember that most meteorites found are the stony variety and not that large. Also, they may not look like what you might think a meteorite should look like. Now, if you do find a large one, it makes it all worth while.

Reg

[Rob in KS]

Reg,
Yes, that was my intention when I heard about Steve Arnold and the big one.

I originally built the first board for a 4" coil. It worked much better than I expected. Then I modified it for the 3 foot coil. I've discovered that its a pretty good relic machine. I can skip all the "small" targets and cover a LOT of ground. Its real easy to push on smooth terrain. I think my depth could be better. I've been pushing it around the farm and digging scrap iron. I need to open it back up and see if I can get more out of it.

All of my targets have been fairly shallow so far. Within a foot. I'm trying to get a feel for the size of the target based on the sound. I use a Garrett with a 12" coil to "pinpoint". Usually the targets have been large enough to find easily. I'll probably re-incarnate it with a larger coil for meteorite hunting

There is a gas pipeline that goes through our property. There is an electric meter and a rectifier box on the pole. They must be pulsing current down that pipe. I can hear it a hundred yards from the pipe. I think its "beating against" the freq of the HH giving me a 1 beep per second. I'll adjust the freq. It nulls when I'm right over the pipe (as near as I can tell).

Any suggestions?

[Reg]

Hello Rob,

If you live anywhere near the area where the pallasite was found, then hunting for other pieces is a real good idea. Actually, any open ground has real potential. The key is to know more about what to expect. Most meteorites are found in open ground. Actually, many if not most found in Kansas were the result of farming and simply removing them from fields.

When hunting for meteorites, it is a good idea to know what to expect from the different types. Most meteorites found are the stony variety and they act more like a piece of basalt or hotrock than a piece of metal. A pallasite or an iron type will respond more like an iron object. Volcanoes are somewhat rare in many parts of Kansas, but there may be some volcanic rock from ancient flows may be around. If not, simply use an old red clay fired brick, like the ones used to build houses and buildings many years ago. Some of these can be quite hot. Something like the brick will show the difficulty in finding some of the stony types because the signal decays to quickly and depth of detection is a problem.

So, you need a fairly short delay to hunt most stony types of meteorites. longer delay works well for the iron types, but as the delay is increased, the sensitivity does go down. You can make some of this up by increasing the number of turns, but not as much as one might hope.

One thing to remember, don't rely on looking at one to recognize it. They don't all look the same and in many cases, do not look like a meteorite at all. Always check any out of place rock, meaning check any rock that doesn't quite match others in an area.

As for changing your detector, and adding depth, you can do this a couple of ways. First, you can increase the gain of the detector at one stage or another. You can reduce the delay as much as possible to try to sample on the strongest part of the signal. Finally, you can experiment with the turns of the coil and coil current. So, what you might do is experiment by adding more turns to your larger coil and see what happens. This is one of the easiest to do if you don't have a sophisticated form of shielding.

Since you are planning on working open fields, you might think about experimenting with a ground canceling coil, or simply making a simple sled type device and slide the coil on the ground. It would be harder to move, but certainly get closer to the ground.

This should get you started.

Reg

[Rob in KS]

Thanks for the great information Reg,

I'm quite a ways from the Pallasite strewnfield, but maybe I'll get lucky. I'm going to run it over the pile of broken brick I have laying around. I didn't realize they could be hot. My main delay might be too long at the minimum.
I didn't realize that a stony would need a short delay.

I'm thinking about building one that uses a micro to drive the timing. Then I can have it vary the delay. That will probably project for the hot summer afternoons. I have a board left over from another project.

I'm going to tweak the frequency to see if I can get rid of the noise from the pipeline and around the house. Maybe 120Hz

Thanks for the suggestions
Rob

[Reg]

Hi Rob,

The most common meteorite is the stony type. There are different varieties of this particular one also. Generally, they refer to the amount of iron or nickel in the meteorite to determine the difference. At least, that is one of the key issues.

Anyway, most of the stony types I have found do not give a strong signal when compared to a piece of iron. If the delay is set back, the signal reduces significantly, depending upon the actual meteorite. Like I said, some stonies will give a stronger signal than others.

One other fact is most stonies that I have found or heard about are small compared to the pallasite found in KS. It seems that the larger meteorites that are the stony type have a tendency to blow up above the earth's surface and spew small pieces down. I have seen pieces as large as a softball, but most are much smaller. A more typical size I have seen or found is in the range of a golf ball, with many being smaller yet.

I am sure there are exceptions, but it is something to keep in mind if you are looking for them.

Again, stonies are the most common and are composed of mostly stone type material with some nickel and olivine as well as other materials. The Chondrites are the most common. The ability to detect them is mainly determined by the amount of nickel and olivine they contain, as far as I know.

Here is something else to keep in mind. Most meteorites that can be detected are attracted to a magnet. The magnetic attraction of a stony can be quite weak but it is there. Some have a stronger pull but again, this is a function of their chemistry, so there is no simple test or substitute.

Because many have fallen a very long time ago, they may not look like what one might expect. The ones I found in AZ have what is called a desert varnish outer surface and do not look like what one would think they should look like. When searching for stony meteorite information, you will run across terms such as L4 and L5 indicating the iron content or maybe a H type, where the L or the H indicate the amount of iron. Obviously, the H type will be easier to detect. Now this iron is in the form of olivine, I think and not solid iron. What generally can be seen in the meteorites is the nickel in the Chondrules.

So, meteorites span a wide range of chemistries and as such, have a wide range of detection capabilities. Some can be very difficult while others of the same size may be detected very easily.

Personally, I recommend people read up on meteorites to learn more about them. It is a really interesting subject.

BTW, it doesn't take a large meteorite to be valuable. If you are lucky enough to find the right one, even one the size of a baseball can be work as much as the pallasite that was found in KS. Unfortunately, such are extremely rare, but they have been found here in the US.

Even a baseball size stony is worth several hundred dollars in most cases. If it is the only one of that area, then the value goes up.

If you think you have found one, then try to find a major university or specialist that can authenticate it. Once it is validated, the value increases dramatically. Also, one has to be careful to not contaminate it if they think they might want to sell it. So, even sampling or testing should be done by experts.

One other bit of wisdom, many meteorites get their name by being named after the nearest post office, which can mean they are named after a town or city. Obviously, there are other reasons for names, but this is used at times.

I gave a lecture some time back at a prospecting club and mentioned to the people to always keep an out of place rock that sounds off on a metal detector. Well, one couple did that and sent the suspected rock to the Denver Museum to be analyzed. It turned out to be a meteorite, fist size, that was estimated to have a street value of $22,000. Not bad for a rock.

I hope this helps.

Reg

[Rob in KS]

You're right about the meteorites being an interesting subject. I hadn't thought too much about the nickel vs iron content. I'm thinking about it now! (sound of hand hitting forehead)

It really sounds like I need to computerize my HH. With the different compositions, I need to be able to vary the timing and do at least a little analysis of the signal. I've been thinking about where to look at the signal. Maybe right after the integrator. The A/D on the board is fast. I've been able to read a signal every 4uS. It's not bipolar, so I'd have to shift the signal above ground. If I use the integrator, I can only read the signal once per coil pulse.

1. Fire the coil
2. main delay
3. sec delay
4. reading

If I do something different, maybe I can read each pulse several times. Maybe do the integration in software. I'm still in the thinking stage. I need to finish my other HH and drag out the micro and do some experimenting. Something to think about while I'm mowing the yard

Thanks
rob