Ham Radio HF Loading Coil / Antenna Project;

[C_M_H]

I'm starting to explore the High Frequency ham bands and made a loaded vertical antenna ( it was a good excuse to learn more about rotary / 4th axis machining as well ).

It came out pretty well, and now I get to learn about "noise floor" and all sorts of other fun stuff....

I turned down some 3/8 - 24 nuts to fit into the copper pipe lower element. The shoulders helped keep the nuts nicely aligned. I soldered it together after it was press fit;



The PVC coil form being cut. I cut a grooved "thread" from one end to the other ( the black is from the Sharpie I used to test the "cut" ).

I love that the G-code to do this is essentially this;

G1 X0.0 Y8.007 Z-0.01 A32400 F51.9965 (G1 Linear Move )
G1 X0.0 Y0.007 Z-0.01 A0.0 F51.9965 (G1 Linear Move )

Start position and rotation, end position and rotation, and time to get there.

If you are into this stuff I used the G93 Inverse Time Mode for the first time, which is necessary for mixed linear / rotary moves;



The finished coil. I made it cover a wide range of bands for testing / educational purposes, and expect to make more based on what I've learned so far.
And yes, having the red lead laying on the coil does affect it's behavior, gotta love the RF.



In action. I was surprised to learn how much the wind can affect a skinny little antenna;

[The Artful Bodger]

FB OM!

How do you tune it?

[Fasturn]

FB OM!

How do you tune it?

I see a sliding shorting ring to tap for the higher bands. Looks like a 75 meter coil ? Of course it depends on the length of the mast and stinger ?? Nice job ! Here is one I made for a friend .
has enough inductance to load up on 60 meters .

DIT DIT ~

[C_M_H]

Tuning is done in 2 parts by adjusting the length of the radials/ counterpoises ( white wires in pic ) and the length of the inductor ( white coil ). I use a device called a "NanoVNA" which gives a graph showing different parameters to be tuned. It's an amazing little tool.

I copied the design of the coil from Wolf River Coils. The white collar near the top ( with the red wire connected ) is a tap point. If you slide the collar up or down it shortens or lengthens the inductor. One benefit of the spiral wound coil is that since it's basically a thread, you can rotate the collar left or right to dial in fine tuning.

Even with a meter it's a bit of a dark art. If you lower the antenna to adjust it things change when you raise it. If you are too close to the antenna it reads differently.

Ah well, I enjoy the process.

I also knocked out some winders to help with wire & string management;

[C_M_H]

Wow, Fasturn, now that's a nice coil. Thanks for posting.

I learned a lot making mine, and can see you know what your doing;

Good aspect ratio ( if I understand correctly this gives a better Q factor?).
Copper wire. My stainless is really resistive...
Air gapped for good cooling.
Brass for no /less induction?...

[Fasturn]

Very nice. I just use the MFJ anylazer and tune for 50 ohm J+0 reactance ,or close as I can get. I like to keep the VSWR under 1.7:1 at the dip. Or return loss under 18. You will need a shunt coil at the feed for the lower frequencies. That antenna will be 12 ohms on 75 meters or something very low. Here is my experimental 160 meter loading coil. Made from 2 EDM wire spools.

[Fasturn]

Wow, Fasturn, now that's a nice coil. Thanks for posting.

I learned a lot making mine, and can see you know what your doing;

Good aspect ratio ( if I understand correctly this gives a better Q factor?).
Copper wire. My stainless is really resistive...
Air gapped for good cooling.
Brass for no /less induction?...

Q is pretty high, but the spacing is for high power. Running a KW on a rainy day , you arc over with the close windings. Also they provide access for coil taps. Here is a photo of some taps ( different bands )
same as your shorting ring. My guess your coil would be good for 500 watts. Mine might handle 2 KW. Not to one up you....... just saying. Have fun with it. A true Ham, building things !!!

[boslab]

Always been tempted to explore ham radio, used to read magazines in the 70s like practical electronics and stuff, I used to like magazines, practical wireless was always good, parts were cheap, vero board and the like, when I moved into my present house the previous owner was a Ham radio enthusiast, the loft was a mess of wire, there were long aerial wires in the garden, a heap of old military radios I gave to a mate, turned out the guy was investigated by the special branch as they thought he was eavesdropping on the military transmitters across the Bristol Channel from me, some navy installations or other.
well made Ariel, reminded me of some sort of Tesla coil thing, cool
mark

[skunkworks]

Dad used pvc tubing like that but threaded it on the lathe...

sam

[Mike Burch]

Wow, Fasturn, now that's a nice coil. Thanks for posting.

I learned a lot making mine, and can see you know what your doing;

Good aspect ratio ( if I understand correctly this gives a better Q factor?).
Copper wire. My stainless is really resistive...
Air gapped for good cooling.
Brass for no /less induction?...

Stainless has about 44 times the resistivity of copper.

Brass has nearly 4 times the resistivity of copper.

A brass-wound coil will have exactly the same induction as a stainless-wound one at the same frequency and current. It's the current that causes the induction, not the material of the conductor.

C_M_H and Fasturn, those loading coils are beautifully made. Congratulations!