Help: Coil Housing Dimensions..

[Aziz]

Oh boys,

problems seam not to disapper. The resin I am using for fixing the coils is shrinking in the drying process. So my balaced coil is buggered up again.

Other glues will probably act in the same way. So I have to think about a flexible adjustable coil design (like Simonbakers probably).

Aziz

[Qiaozhi]

Oh boys,

problems seam not to disapper. The resin I am using for fixing the coils is shrinking in the drying process. So my balaced coil is buggered up again.

Other glues will probably act in the same way. So I have to think about a flexible adjustable coil design (like Simonbakers probably).

Aziz

Why don't you try an omega configuration with the receive coil on a moveable plinth. This is the way Heathkit designed their coils.

[Aziz]

Hi Qiaozhi,

Why don't you try an omega configuration with the receive coil on a moveable plinth. This is the way Heathkit designed their coils.

thanks for the picture. It is really a good idea. Making the receive coil somehow adjustable with (plastic) bolts and nuts.
Well, I am collecting some practical experience yet. I have now fixed my coils very tight regardless of balance condition. Put some "whipped cream" again and now waiting for the "baken cake". I will take an extra coil winding for fine balance later when the coil is almost finished. This seams the easiest way.

The next coils will be completely of different design of course. This time is just for investigating of problems of coil designs.

Aziz

[simonbaker]

Why don't you try an omega configuration with the receive coil on a moveable plinth. This is the way Heathkit designed their coils.

Heathkit not afraid of metal screws!

For field coil, I was thinking similar -- adjustable, but not whole coil, just single loop glued to board, with plastic screw to outside! But not good for you, too easily vibrated -- you need adjustable with no vibration. So like Qiaozhi show, only just extra loop, then glue sucker down after all other glues cure.

Then have fun when sun heats it!

If it was easy, everybody would be doing it...

Good work, keep going.

Cheers,

-SB

[Aziz]

Additional small loop of winding brings the comfortable and easy coil balancing. I could had spared much time and effort with it. Now the mechanical stability and weight is the most important issue. More pictures coming soon...

Aziz

[Qiaozhi]

[quote=simonbaker;79594]Heathkit not afraid of metal screws!/quote]

Worse than that!
Can you see the 4 holes on the casing, where the other half of the coil housing is attached?
These are also metal screws!!

[Esteban]

[quote=Qiaozhi;79608]

Heathkit not afraid of metal screws!/quote]

Worse than that!
Can you see the 4 holes on the casing, where the other half of the coil housing is attached?
These are also metal screws!!

When you adjust these Heathkit coils, screws and PCB must be present for to include in final adjustment. Important: electrolitic must be fixed with glue for to prevent vibration and ringing. If you paint the coil housing, after adjustment, use synthetic paint, no based in metalic ores. This destroy the final zero!

[Max]

[quote=Esteban;79616]

When you adjust these Heathkit coils, screws and PCB must be present for to include in final adjustment. Important: electrolitic must be fixed with glue for to prevent vibration and ringing. If you paint the coil housing, after adjustment, use synthetic paint, no based in metalic ores. This destroy the final zero!

At the end... he will make an LRL!

[Qiaozhi]

[quote=Esteban;79616]

When you adjust these Heathkit coils, screws and PCB must be present for to include in final adjustment. Important: electrolitic must be fixed with glue for to prevent vibration and ringing. If you paint the coil housing, after adjustment, use synthetic paint, no based in metalic ores. This destroy the final zero!

Yes - you are correct.
The coil in the photo is factory-made, but an earlier similar Heathkit design could be balanced through a small hole in the back of the search head. As long as you balance the coil with all the parts present, then the detector will work ok. It would be an interesting experiment to test whether metal parts in the search head cause any decrease in sensitivity. It is not uncommon, in commercial detectors, to see metal screws where the coil is connected to the shaft, or even metallic labels stuck on top of the coil.

[Esteban]

[quote=Max;79629]

At the end... he will make an LRL!

For this purpose I prefer the GD-48, not the GD-348.

[simonbaker]

[quote=Qiaozhi;79633]

Yes - you are correct.
The coil in the photo is factory-made, but an earlier similar Heathkit design could be balanced through a small hole in the back of the search head. As long as you balance the coil with all the parts present, then the detector will work ok. It would be an interesting experiment to test whether metal parts in the search head cause any decrease in sensitivity. It is not uncommon, in commercial detectors, to see metal screws where the coil is connected to the shaft, or even metallic labels stuck on top of the coil.

I think that is good question -- we always assume can't have any metal, jump through hoops to avoid. Maybe just a little constant phase shift, taken out by motion filters or balancing.

Big metal bad though I think, reduce Q of TX coil.

Good to retest old assumptions occasionally.

-SB

[Esteban]

[quote=Qiaozhi;79633]

Yes - you are correct.
The coil in the photo is factory-made, but an earlier similar Heathkit design could be balanced through a small hole in the back of the search head. As long as you balance the coil with all the parts present, then the detector will work ok. It would be an interesting experiment to test whether metal parts in the search head cause any decrease in sensitivity. It is not uncommon, in commercial detectors, to see metal screws where the coil is connected to the shaft, or even metallic labels stuck on top of the coil.

In this design also the shield portion cable inside must be in his final place with his curves, etc.

If you put a hand in both side of receiver coil you note that the capacitive effect increases audio in a side and decreases in other side (here detector you must put in low audible signal for to note it). I prefer the increasing of audio when bring over the hand in the side of the receiver coil wich his near the soil. When you put near the soil the audio increases and you can adjust with the sensibility potentiometer. But if you put near the soil and the audio decreases, sensibility is poor. Inverting the cables of extremes you achieve it. But I note this in the GD-48, don't know in the GD-348 you show in the pic. Other considerations in pic for the GD-48. This work as a nulling coil and you note better if the cable is more long.

Regards

Esteban

[Esteban]

[quote=simonbaker;79637]

I think that is good question -- we always assume can't have any metal, jump through hoops to avoid. Maybe just a little constant phase shift, taken out by motion filters or balancing.

Big metal bad though I think, reduce Q of TX coil.

Good to retest old assumptions occasionally.

-SB

Big metal is negative here. But for to correct final zero or when zero was moved from original or fo to obtain better zero, you can use head of screws glued in the coil housing for to correct it, or directly the entire screw glued in vertical position. Can be some hardzarous! And there is more. You must try the kind of screw, based on iron, bronze or bronze-iron, etc. Do you see why is hardzarous?

[Esteban]

IS WORKING GOOD THE QUOTATION TOOL?

[Aziz]

One important aspect found: glueing the coil to the coil housing will cause false signals on mechanical shocks applied to the coil. So it is not recommended to glue the coils to the coil housing as I did. They should be isolated via PU foam or something similar shock absorbing material.

In the following images you can see further steps of coil assembly. Finally the null balancing winding in the center position. This can be even smaller to give better stability. It depends on the accuracy of the preliminary mechanical balancing accuracy. The null balancing winding is connected in series with the RX coil.

Next steps: One layer fibre glass for the bottom side of the coil housing to fix the coil assembly. Then a bottom graphite faraday shielding. After that, the finaly fibre glass bottom side to protect the shielding and coil.

Aziz