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[Articles Home]  [Add Article]  

Make Your Own Loading Coils

K0FF (K0FF) on January 14, 2010
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KFF Homebrew Tips

Subject: Make Your Own Loading Coils DE KFF

OR: "If they look like DUX and walk like DUX and quack like DUX, maybe they

ARE DUX"

(then again maybe not)

"Air Dux" inductors were once plentiful and inexpensive. Not so today. Even if they were, HAMs

like to make their own apparatus when possible. Here is one method that I have long used to

make evenly spaced, nice looking coils of all sizes.

Make your own loading coils for antenna projects using Caterpillar Grommet

strips. Also called flexible grommets, flexible bushings etc.

These are used by installers to form protective bushings around the edges of holes cut into sheet metal,

and come in strips that are cut to desired length then snapped into the hole to cover the raw edge.

We used to use them when installing 2-way radios to line the holes we made in the firewall to pass the heavy 12V wires.

The evenly spaced notches make an ideal form and support for AIR DUX knockoffs. Use Duco or Testors model

cement to secure the wires in the strips before removing from the temporary

forms. Nylon Grommet strips can be purchased atMcMasters, as well as many other supply houses.

Fig 1 is the caterpillar grommet material as purchased from the supplier:

Fig 2 - Next Wrap the form (whatever size you need) in wax paper and temporarily

tape the plastic strips on there:

Fig 3 -Wind the coil using the notches as a guide. Seat the wire all the way down

into the notch and wrap the coil tightly. Spread plastic cement down the

strips when the coil is wound:

Fig. 4 - When the glue is dry, slip the assembly off the form and trim the strips to

correct length:

Fig 5 - Any size diameter or length can be wound, just use bigger forms and more

strips:

Happy Building, Geo>KFF

Member Comments:
This article has expired. No more comments may be added.
 
Make Your Own Loading Coils  
by K6SI on January 14, 2010 Mail this to a friend!
George: You are a genius. Excellent idea... now why didn't I think of that? Ken, K6SI.
 
Make Your Own Loading Coils  
by AI4WM on January 14, 2010 Mail this to a friend!
That is a great idea! I agree with the previous post "why didn't I think of that". Your idea is one of those creative ideas that really works. I have seen some other way too complicated methods for making coils. Thank you for sharing it with all of us.
73,
Bill
 
Make Your Own Loading Coils  
by K5END on January 14, 2010 Mail this to a friend!
I gotta say, using caterpillar grommet strips for coil spacers is certainly thinking outside the box, and in a very intelligent way.

Your idea is flame proof.

I think you have started a new method that may be used for a long time.

Well done, and thanks for posting the idea to share it with the community.
 
Make Your Own Loading Coils  
by K5END on January 14, 2010 Mail this to a friend!
Looks like the idea is a popular one. :) (SRI)

http://www.ad5x.com/images/Articles/CoilRevB.pdf
 
Make Your Own Loading Coils  
by N5TGL on January 14, 2010 Mail this to a friend!
Very cool and simple. Even big ol' 6" coils would be easy with this method.
 
RE: Make Your Own Loading Coils  
by AD5X on January 14, 2010 Mail this to a friend!
Great article! I've been doing something very similar for awhile (see the "Articles" section at www.ad5x.com). I drill holes in the PVC pipe to pass the wire ends through to make it easier to tightly wind the wire. I use tie-wraps instead of electrical tape to hold the nylon trim in place. And I use hot glue to hold the wire in the nylon edge trim, though 2-part epoxy is really great (but messy) for a rugged mobile coil. My website article also shows how to build coil supports from plumbing parts and fiberglass bicycle flag rod.

The McMaster part number of the nylon edge trim I use is 85085K8, and a package of 25 strips, each 12.75" long are $11.33 - plenty to make a lot of coils. #14 solid copper wire is a nice fit for this nylon trim. McMaster 8873K51 is $20 for 80 feet - though it is probably cheaper through Lowes or Home Depot (didn't think of that until after ordering the wire from McMaster - and 80' has lasted me a long time).

Phil - AD5X
 
Make Your Own Loading Coils  
by K9CTB on January 14, 2010 Mail this to a friend!
George, you are an engineer's engineer!!! What a great idea. Like others, I wish I'd have thought of it, but I have no talents whatsoever except an enormous talent for appreciating people who actually do!

73 de Neil
K9CTB
 
RE: Make Your Own Loading Coils  
by KI4WGI on January 14, 2010 Mail this to a friend!
As a manufacturing engineer, I can appreciate the "coolness" of this idea. If I ever need to wind a coil of this type, I'll be using your "process".
 
Make Your Own Loading Coils  
by N0SAP on January 14, 2010 Mail this to a friend!
WOW, I agree with the other hams, what a great idea. I like building antennas and winding coils has always been a challenge. I built a 3 element 30 meter beam that I put up this fall which works GREAT. This idea gets me excited to design some more homebrew beams over the Winter. So now I will be ready for Spring, Hi, Hi. "SAP"
 
RE: Make Your Own Loading Coils  
by KG6WLS on January 14, 2010 Mail this to a friend!
George, thanks for the tips you provide. You make home brewing fun. I built several 2M & 6M loops from your article years ago (with success) and always look forward to see more from you.

73 de KG6WLS
Mike
 
RE: Make Your Own Loading Coils  
by K0FF on January 14, 2010 Mail this to a friend!
Yes the technique has been around a long time. I originally published this on Towertalk and my first webpage in 2000.

Geo>K0FF
 
Make Your Own Loading Coils  
by KJ4NBM on January 14, 2010 Mail this to a friend!
Very good idea!! Can air coils also be wound with regular insulated wire using this method? Will the inductance be changed that much?

I don't have any enamel coated wire but have plenty of 12 GA insulated wire, so if I can use it I won't need to purchase enamel magnet wire.
 
RE: Make Your Own Loading Coils  
by K1XT on January 14, 2010 Mail this to a friend!
I've been using this method for about 20 years. I now use hotglue as it seems to hold up just as well and will flex when need be. Also, if I want to make some adjustments in the coil, I can melt the glue again and lift out a turn or two. For a 'hard' coil I glue the strips in place on the PVC and put caps on each end. I have two that I use in a mobile application on 2 inch PVC, 14ga. They work very well.
 
Make Your Own Loading Coils  
by AB7E on January 14, 2010 Mail this to a friend!
Very nice idea from K0FF ... simplest way I've seen so far to space and secure air wound coils.

To KJ4NBM: Personally, I'd strip the insulation to reduce the interwinding capacitance. Why would you need to use enameled wire anyway, though? Bare wire works just fine.

73,
Dave AB7E
 
RE: Make Your Own Loading Coils  
by K1XT on January 14, 2010 Mail this to a friend!
Bare wire is fine as mentioned. It also allows you to tap the coil anywhere you wish. That's the way I use it in my mobile applications. I jumper across the turns and I can go for a perfect match.
 
RE: Make Your Own Loading Coils  
by N2EY on January 14, 2010 Mail this to a friend!
BRILLIANT!

How does nylon take RF?

73 de Jim, N2EY
 
RE: Make Your Own Loading Coils  
by K0FF on January 14, 2010 Mail this to a friend!
the Q was:
"How does nylon take RF? "

A: Nylon, Teflon and Derlin look very much alike when in a block or rod.
To test any material's RF capability, expose it to about 700W @ 2450 MHz ( i.e. put in in the microwave oven!)

Nylon gets hot and melts quickly.

Not good for RF environments. Also it absorbs moisture.

Use Derlin when possible.

PVC, Nylon, Teflon and Derlin all measure infinite Ohms on an Ohmmerter.

While PVC is fine for low power applications ( both as insulators and as coating on wires like power wiring), it melts easily when exposed to heat. AT high power, coils get hot.

Once I was building a power amp for HF and in a rush wound an experimental tank coil out of house wiring with the PVC still on. It caught on fire.

All antennas, verticals included have high current/low voltage and high Voltage/ Low current points along their length.

A simple 1/4 wave Marconi antenna has the high current point at the feedpoint. At the end of the wire, there is a LOT of Voltage (try a florescent tube out there!)

Therefore chose your insulators according to their location and expected power levels. *End Insulators* should always be glass or porcelain.

Geo>K0FF
 
RE: Make Your Own Loading Coils  
by AH6RR on January 14, 2010 Mail this to a friend!
Great work and a very good demostration of using your noodle, someting I need to do alot more of. Now I need to figure out what I want to build using this method.
Roland AH6RR
 
Make Your Own Loading Coils  
by DROLLTROLL on January 14, 2010 Mail this to a friend!
Don't forget you can make your own glue too in order to hold the coil winding in place. Just dissolve styrofoam in acetone till it gets thick and gooey, apply onto your coil and spacer with a small brush. That's how we did it in the 'olden days'.
 
RE: Make Your Own Loading Coils  
by N3OX on January 14, 2010 Mail this to a friend!
"Personally, I'd strip the insulation to reduce the interwinding capacitance. Why would you need to use enameled wire anyway, though? Bare wire works just fine"

For very high reactance loading coils in critical applications, it's probably useful to use enameled wire to reduce leakage resistance effects after the whole coil gets dirty.

An X=1000 loading coil with Q = 300 has a parallel equivalent resistance of something like 300 kiloohms.

Interwinding capacitance is a big problem with such a coil too, so I wouldn't use thick insulation, but I wouldn't necessarily shy away from using thick enameled wire if I had it.

I spray my coils that are on forms with electrical varnish these days. It probably doesn't actually matter, certainly not in a practical way, but it'll make me feel better after the coil gets all covered with damp cobwebs and my PVC forms get wet and dirty.

http://n3ox.net/projects/stepperswitch/160_match_lg.jpg

http://n3ox.net/projects/stepperswitch/40m_match_lg.jpg

In my particular case, it's really just decoration, because other losses associated with my vertical and coils almost certainly swamp leakage considerations... and of course the extra self-capacitance due to the form matters.

With less surface area like with these strips, leakage resistance would be much lessened. But I'd probably varnish my coils anyway. I wouldn't leave PVC THHN insulation on though... it's easy enough to strip off. I can do enough wire for a big coil in a few minutes using a pocketknife and practice.

73
Dan
 
Make Your Own Loading Coils  
by KJ6BSO on January 14, 2010 Mail this to a friend!
Give that man a CEE-gar!
 
RE: Make Your Own Loading Coils  
by K7AAT on January 14, 2010 Mail this to a friend!
The key to the coil project is the nylon spacer material from McMaster-Carr . I just wanted to point out that N1LO website at
http://www.qsl.net/n1lo/mobilhf.pdf
has been showing this manner of coil construction for well over 10 years. Kudos to anyone who helps disseminate this procedure, though.

Ed K7AAT
 
RE: Make Your Own Loading Coils  
by WA2JJH on January 14, 2010 Mail this to a friend!
EXCELLENT!

I make my own verticals out of scrap. Perhaps I will be able to build one of those $200-$300 verticals for a few bux and PVC masting/support tubing.

Keep up the gud tech artls.
 
RE: Make Your Own Loading Coils  
by K0FF on January 14, 2010 Mail this to a friend!
K7AAT said:

" The key to the coil project is the nylon spacer material from McMaster-Carr . I just wanted to point out that N1LO website at

http://www.qsl.net/n1lo/mobilhf.pdf "

K0FF Says: RR and amen to that. I was first introduced to the method in the 1960's by my friend and neighbor W0DYI (SK). Gateway Electronics of St. Louis had this material and many other things that you wouldn't normally find lying around, making for a very creative ham community there. Oh how I miss those WW2 Arc-5 sets, all you wanted for $5 each, TX, RX, Modulator, PS....all different bands etc.

Today we have far fewer surplus electronics places, but we do have the internet. Distribution of ideas among hams is key. I encourage anyone who has a gimmick or method to take pictures and post it on eHam, for all of us to benefit.

73 Geo>K0FF
 
RE: Make Your Own Loading Coils  
by G3LBS on January 14, 2010 Mail this to a friend!
Excellent logical step-by-step program and pictures. Could you come and teach my classes?
Many thanks
Gil
 
RE: Make Your Own Loading Coils  
by KE7FD on January 14, 2010 Mail this to a friend!
Great idea George! Go ahead and take the rest of the day off.

KE7FD
 
RE: Make Your Own Loading Coils  
by K1XT on January 14, 2010 Mail this to a friend!
Hey George,

That's where I obtained my nylon strips, Gateway. I still have a bag of them here. Always a good place to go and think out a project. I miss Saturday mornings at Gateway with Stu and the others.
 
RE: Make Your Own Loading Coils  
by ZENKI on January 15, 2010 Mail this to a friend!
Great Article

I was just reading the article in this Months QST by W6YE. W6YE made those exact strips on a table saw. Maybe W6YE will read this article and save himself a lot of trouble. Making those strips must be a lot of work.

Anyway W6YE's article is a "keeper" for future reference along with this Eham article on making coils. AD5X also has a great deal of information on making coils. I like his Bugcatcher style of coil construction

Anybody going to open a Bug Catcher coil factory soon ?
Caterpillar Bugcatchers!

Looking at the price of B&W Air Dux coil made of No10 wire, you would swear its made out of gold its just so expensive.

MFJ will start selling these strips of plastic soon LOL
 
RE: Make Your Own Loading Coils  
by ZENKI on January 15, 2010 Mail this to a friend!
Great Article

I was just reading the article in this Months QST by W6YE. W6YE made those exact strips on a table saw. Maybe W6YE will read this article and save himself a lot of trouble. Making those strips must be a lot of work.

Anyway W6YE's article is a "keeper" for future reference along with this Eham article on making coils. AD5X also has a great deal of information on making coils. I like his Bugcatcher style of coil construction

Anybody going to open a Bug Catcher coil factory soon ?
Caterpillar Bugcatchers!

Looking at the price of B&W Air Dux coil made of No10 wire, you would swear its made out of gold its just so expensive.

MFJ will start selling these strips of plastic soon LOL
 
Make Your Own Loading Coils  
by K1KO on January 15, 2010 Mail this to a friend!
George,

Great idea, great post. Congrats on submitting the first post to e-ham forums that DIDN'T get flamed!! I'd have that put on my tombstone.

73,K1KO
 
Make Your Own Loading Coils  
by KB2DHG on January 15, 2010 Mail this to a friend!
FANTASTIC! simply FANTASTIC...
You get the E-HAM's tip of the year award for this one my friend!
 
RE: Make Your Own Loading Coils  
by K0FF on January 15, 2010 Mail this to a friend!
K1XT said: "Hey George,

That's where I obtained my nylon strips, Gateway. I still have a bag of them here. Always a good place to go and think out a project. I miss Saturday mornings at Gateway with Stu and the others. "

My goodness yes Bill. St. Louis was a wonderful place to grow up in the radio hobby and business. We had Walter Ashe Radio,
Gateway Electronics ( surplus), Olive Electronics and Van sickle Electronics for new parts.
Later we had Ham Radio Center ( Bill Du Bourd orig. from Walter Ashe- Bill invented the "800" number and discount pricing), Midcom, Walcom ham radio stores.

I myself even ran a ham radio store out of my 2-way radio shop for a few years.

Stu and Lou at Gateway were friends and mentors to all radio people in the area. They made us comfortable and fed us coffee on Saturday mornings, and a couch to sit and talk about radio and exchange ideas.

I hope that eHam becomes our greater "couch" in years to come.

Geo>K0FF
 
RE: Make Your Own Loading Coils  
by W0FM on January 15, 2010 Mail this to a friend!
Hey George,

Before I was married in 1996, my bride-to-be finally insisted that I take her to "that Gateway place you go to every weekend". I eventually took her along. Introducted her to Stu, Lou and the crew. She was dumbfounded as we walked up and down the aisles of cherished pieces of nothing. Needless to say, there were many eyes following her along the way. Not many women in Gateway in those days. Everyone seemd to end up in the same isle we were in. ;o)

Those WERE the days! Great article.

Terry, WFM
 
Make Your Own Loading Coils  
by EA2BSN on January 15, 2010 Mail this to a friend!
Nice work!

You will find here a video with a similar process using corrugated tube:

http://www.youtube.com/watch?v=EyTAq1XbE1k

73
 
RE: Make Your Own Loading Coils  
by K0FF on January 15, 2010 Mail this to a friend!
W0FM said:
"Hey George,

Before I was married in 1996, my bride-to-be finally insisted that I take her to "that Gateway place you go to every weekend". I eventually took her along. "

Let's be careful about giving away our ham secrets. It wouldn't do to have the wives find out that "those overnight Field Day Weekends" actually DON't happen once *every* month!

Geo>K0FF
 
RE: Make Your Own Loading Coils  
by W9OY on January 15, 2010 Mail this to a friend!
Not sure how testing some nylon in a microwave oven tells you anything about how it behaves at 1.8 mhz, but I love this idea.

73 W9OY
 
RE: Make Your Own Loading Coils  
by W8AAZ on January 15, 2010 Mail this to a friend!
If you ever price old stock or even new stock of airdux coils on ebay, you gotta shake this guy's hand and thank him. They sell for way way too much nowadays. Except if you get lucky in a hamfest junk box.
 
RE: Make Your Own Loading Coils  
by N1LO on January 15, 2010 Mail this to a friend!
Hi George,

Thanks again for this tip.

I've been building coils this way for 10 years now since you first mentioned this trick on the Towertalk reflector way back around '99 or so.

I've been using hot melt glue. Painting the strips first with a light coat of flat black paint greatly improves the bond!

see my aging (2001) plan at http://www.qsl.net/n1lo/mobilhf.pdf

I gave up the wire cap hats long ago in favor of inverted L construction. See my listing on
http://www.qrz.com for a more recent version.

Regards,

--...MARK_N1LO...--
 
RE: Make Your Own Loading Coils  
by VE3FMC on January 16, 2010 Mail this to a friend!
Hi Geo

Brilliant, simply brilliant. Well written, well documented and great photos.

A superb do it yourself project.

Rick VE3FMC
 
RE: Make Your Own Loading Coils  
by VE3FMC on January 16, 2010 Mail this to a friend!
Hi George

Brilliant, simply brilliant. Well written, well documented and great photos.

A superb do it yourself project.

Rick VE3FMC
 
Make Your Own Loading Coils  
by KC0NIB on January 16, 2010 Mail this to a friend!
This is indeed a neat idea when making these things. There is only one slight problem. I have discovered that in my part of the country, due to the abundance of thieves who steal copper, finding the copper "magnet" wire is next to impossible.

If you can, I'd suggest sharing a location that can sell the stuff. It ain't available around the parts here in Minneapolis. I went looking some time back and discovered I'd have to order from out-state.

Cheers and 73
 
RE: Make Your Own Loading Coils  
by K0FF on January 16, 2010 Mail this to a friend!
Mark said:
"Hi George,


see my aging (2001) plan at http://www.qsl.net/n1lo/mobilhf.pdf

I gave up the wire cap hats long ago in favor of inverted L construction. See my listing on
http://www.qrz.com for a more recent version.

Regards,

--...MARK_N1LO...--"

Hi Mark, well first of all thanks for the drawing of the mobile antenna, very cool!

Second, thanks for the link to the QRZ site. So far I can't find your article, but I will. Can you believe I didn't know about that site at all? I'm a self confessed computer dummy. Need to "get out" more my wife says, but I'm pretty satisfied tinkering down in my basement.

I really like mobile operations and have tried many antennas. Once I had a simple setup with a coax cable running from the van into the shack, so I could A-B compare the mobile antenna to my R7 vertical mounted on a fence. When the mobile antenna got the same signals strength as the big vertical, I knew it was good enough.

This is on 20M and up I should add.

80/40 are a different story on a car, mostly due to the height requirements levied by bridges and overpasses.....

Don't lets all forget that the vehicle itself is the "other half of the antenna". Once I backed up two identical vans to within a foot of each other and loaded them up as a "fat dipole". Worked rather well.

73 Geo>K0FF
 
Make Your Own Loading Coils  
by W4HKL on January 17, 2010 Mail this to a friend!
Sweet! Even a total clutz like myself can (probably) master this method.

Thanks for sharing this in a well-written article,

Steve, W4HKL
Caryville, TN
 
RE: Make Your Own Loading Coils  
by KB2CPW on January 17, 2010 Mail this to a friend!
This wins the 2010 ultra cool ham award!! Bravo!!
 
RE: Make Your Own Loading Coils  
by K6LO on January 17, 2010 Mail this to a friend!
Thank you for sharing this really simple way of making such nice homebrew inductors. Great practical article!
 
RE: Make Your Own Loading Coils  
by N1LO on January 17, 2010 Mail this to a friend!
George,

If you send me an email
(N 1 L O at h o t m a i l dot com)
I'll send you some pics of unique coils I've made with this process.

The email address you have on your qrz.com listing bounced.

Mark
 
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