Flat Spiral wound....Is my method sound?

[Ism]

I haven't spent much time on the coil as of late as I have some other things to tend to but hope to dig in this weekend and make some headway.
WM6, sometimes I can't see the forest for the trees (forgot about my LCR meter). I measured my makeshift cap and it was around 3pf. I reduced it to as close to 1pf but my meter is a little jumpy.
Its supposed to be a pretty good LCR, but I just can't get it to stabilize at that low of a reading. SRF is now 2.4MHz for the coil alone.

Thanks for the info Dan, I will keep you posted after feed line coax and shielding.

[Ism]

In regards to the damping resistor, in the past I placed them in the coil, but I was thinking that to keep solder joints to a minimum, I should place the damp resistor in the connector at the end of the coax feed line. (5 pin mic connector)
I couldn't find any posts that spoke of it. One drawback is the damping resistor is limited to around 1/4 watt in order to fit it in the connector.
I've had them get fairly hot at the coil when they were that small. What are your thoughts on that idea.

[6666]

In regards to the damping resistor, in the past I placed them in the coil, but I was thinking that to keep solder joints to a minimum, I should place the damp resistor in the connector at the end of the coax feed line. (5 pin mic connector)
I couldn't find any posts that spoke of it. One drawback is the damping resistor is limited to around 1/4 watt in order to fit it in the connector.
I've had them get fairly hot at the coil when they were that small. What are your thoughts on that idea.

You can series the 1/4 watters to spread the power
dissipation , or parallel them, what ever works for you.

[Qiaozhi]

In regards to the damping resistor, in the past I placed them in the coil, but I was thinking that to keep solder joints to a minimum, I should place the damp resistor in the connector at the end of the coax feed line. (5 pin mic connector)
I couldn't find any posts that spoke of it. One drawback is the damping resistor is limited to around 1/4 watt in order to fit it in the connector.
I've had them get fairly hot at the coil when they were that small. What are your thoughts on that idea.

There are advantage and disadvantages to all three approaches.

1) Putting the damping resistor inside the coil shell limits the coil to being used by one particular detector, as the same coil may require a different damping resistance when used on a different machine.
2) Putting the damping resistor inside the coil connector is problematic, mainly due to the limited space available inside the connector.
3) Putting the damping resistor inside the electronic enclosure limits the detector to coils that will work with the selected damping resistance.

If you're using a commercial coil, then you only have options 2 and 3 available.
Putting the damping resistor inside the coil shell is not really an issue, unless you're Minelab, and are working at the limits of detectability.

Personally, I put the damping resistor inside the coil shell so that it matches the coil exactly. But I also have one installed inside the electronics enclosure across the back of the coil connector socket. By using appropriate wiring to the coil socket, you can either plug in a coil that has its own resistor, or one that doesn't. In the latter case, jumpers inside the coil plug will either place the damping resistor in or out of circuit.

[ODM]

Measuring very low capacitances and inductances is very touchy about the measurement setup. Parasitic L, C, R is easily added as well as coupling.

Are you sure your lower resonance around 700khz isn't your primary resonant frequency? Secondary resonances generally appear above, not below, unless they are due to your measurement setup. The first peak you see would be much lower but could still be high. It is passed through the pF gimmick, then shunted by your coil, then passed thru another gimmick and ultimately shunted by your scope input impedance which is mostly capacitive at those frequencies.

[Ism]

Thanks ODM for the reply.
Well from what I can tell, there are harmonics all up and down the spectrum. However at 2.4MHz, it jumps greatly.
But what I will do, is make a youtube video in the future and demonstrate for the experts to weigh in.

I did decide to go ahead and place the damping resistor(s) in the coil but I already have a screw-up (typical for me).
1. I based my coil size on the bottom coil shell not the top. As you may already have figured out, the top fits into the bottom and is smaller in diameter.
I may be able to reduce the size of the overall coil by putting it on a belt sander and removing some of the hot glue I used to seal the end. But if I make one mistake, I'll hit the coil winding so it will be touch and go.

2. The tape I used to maintain a gap in the shielding wasn't adequate and the Aquadag bridged the gap under it. So I have two problems.
As far as the Aquadag, maybe somebody knows of a decent solvent? Maybe the same alcohol that it is suspended in?

I may have to start all over.....UGH!

[Ism]

Thanks ODM for the reply.
Well from what I can tell, there are harmonics all up and down the spectrum. However at 2.4MHz, it jumps greatly.
But what I will do, is make a youtube video in the future and demonstrate for the experts to weigh in.

I did decide to go ahead and place the damping resistor(s) in the coil but I already have a screw-up (typical for me).
1. I based my coil size on the bottom coil shell not the top. As you may already have figured out, the top fits into the bottom and is smaller in diameter.
I may be able to reduce the size of the overall coil by putting it on a belt sander and removing some of the hot glue I used to seal the end. But if I make one mistake, I'll hit the coil winding so it will be touch and go.

2. The tape I used to maintain a gap in the shielding wasn't adequate and the Aquadag bridged the gap under it. So I have two problems.
As far as the Aquadag, maybe somebody knows of a decent solvent? Maybe the same alcohol that it is suspended in?

I may have to start all over.....UGH!

Aaahhh, salvaged it last night at work. Still need to repair Aquadag bridge over gap, but it fits in the housing now.