Skip to content

The K1YPP Magnetic Loop Antenna

May 25, 2019

The K1YPP Magnetic Loop Antenna

Note to my readers of this blog: I’ve decided to expand the blog to include various other interests I have. Up until now everything that I’ve posted has been strictly about writing and author related topics. Since I have varied interests, such as ham radio, bicycling and hiking, for example, I’ll be including topics related to those fields. This post is about an antenna that I have been researching for several years for amateur radio (also known as “ham radio”). There is a Youtube video of this project at: https://www.youtube.com/watch?v=B-tYtbTts0s

IMG_3520

I’ve been living in a home owner’s association (HOA) for some time now and have been on the air as an amateur radio operator. There are challenges, but one can get on the air in an HOA.

I’ve been experimenting with Magnetic Loop Antennas, (MLA’s) for years. They are small, light-weight, and have excellent local electrical noise rejection. For years I had avoided building one because most of the designs involved a daunting array of expensive vacuum capacitors, fancy welding and brazing, special low-resistance materials, etc.

My new antenna would have to meet three requirements:

  1. Cost $50.00 or less (excluding remote tuning devices, such as motors, hydraulics, etc.).

  2. Cover 40, 30 and 20 meters.

  3. Have a minimum power limit of 30 watts ( for CW and PSK31).

The primary challenge is to keep resistive losses to a minimum. Many MLA designs use large diameter copper pipes and silver-soldered joints. Builders favor vacuum capacitors or butterfly capacitors that have no electrical contacts or brushes because the contacts will overheat.

Based on the calculations on Steve Yates’ (AA5TB) web page Small Transmitting Loop Antennas, I settled on a four-foot diameter for the desired frequencies. My initial prototypes used folded aluminum foil on PVC pipe, but the foil was too difficult to work with, especially if outdoors in a windy location. I then tried aluminum weather-seal tape and found success.

Figure-2

Parts before assembly. The PVC-to-CPVC adapters are not shown.

I formed the loop with 12 feet of the flexible ¾ inch Sharkbite PVC and used two straight pieces of a larger ¾ inch diameter PVC (Lowes # 23990) to form the capacitor. ¾ Inch copper tubing fits nicely inside this particular PVC tubing, without too much “slop.” I used a continuous piece of aluminum foil tape (2 inch width) spiral wrapped around the loop and down along the two tubes that formed the “capacitor.” The tape I used was made by Nashua Corp, and has a sticky back with a blue plastic cover over the glue. I didn’t remove the plastic, it made construction easier and less messy. The only soldering is the SO-239 coaxial connector. In the first prototype, I wrapped folded aluminum foil in a spiral around the loop and then around the vertical tubes, but the spiral proved to be problematic for the capacitor. The contacts between the spiral as it wrapped down the vertical tube provided contact resistance and the resulting high currents affected the SWR. I found a solution by leaving a gap in the spiral wraps so that the foil did not overlap or touch.

IMG_3521

The capacitor is actually a form of “Butterfly” capacitor, formed by the outer foil on one tube, the “trombone” copper tubing, and the foil around adjacent tube. When purchasing the vertical tubing, make certain the 3/4 inch copper tubing will fit inside the plastic tubing. There are many variations so careful selection is necessary to insure the copper will slide inside the plastic tubing. To adapt the CPVC “TEE” fitting to the vertical tubes, I used a PVC-to-CPVC adapter (Lowes #65322) with a small section of Sharkbite tubing inside. The parts are all held together with some self-tapping screws, glue isn’t needed. With the dimensions used, the capacitor measures about 200 µF per foot, giving a total of about 100 µF/foot for the two legs being in series. The 40 M band needs about 160 µF of capacitance, so the legs have to be about 22 inches. The good news is, since the capacitor goes through two pieces of plastic tubing, the voltage rating doubles. PVC is rated at about 140 kV/CM, so this configuration should be good for about 20 kV.

Tuning the capacitor is a matter of sliding the “U” shaped copper tubing “trombone” up or down in the capacitor to achieve resonance.

I made a small feeder loop to couple to the main loop. I soldered a SO-239 coaxial connector to common household #12 electrical wire, about a foot in diameter. I then attached the small loop at the top of the MLA and coupled it tightly to the main loop. Using an antenna analyzer, I adjusted for best SWR. This proved easier than anticipated. A loop about one-fourth to one-fifth the diameter of the main loop worked best.

Construction

MLA-plastic-assy-Nashua-tape-version

Simply cut the plastic pieces to length and plug them together. You can also use duct tape during the wrapping process to hold the aluminum in place. To form the U-shaped “trombone,” notch the copper pipe with a hacksaw or “crush” it in a vice, and then bend it to ninety degrees. For a more “finished” look, one can heat the copper to red-hot, then let it cool slowly. Then, fill it with sand or salt, then bend it over a round surface. Look around on Youtube for various methods.

Wrap the foil starting at the bottom of one capacitor tube, follow up around the loop and then down the other capacitor tube. Keep a small gap between windings on the capacitor tube, about a 1/4” is sufficient.

After wrapping the foil, mount the small loop with duct tape or tie wraps, and then insert the “trombone” copper tubing. The antenna is now ready for testing.

Testing

With an antenna analyzer

I used an MFJ antenna analyzer for the testing phase. If one is not available, see the instructions below for testing with a transmitter and receiver.

To test, push the “trombone” all the way into the capacitor tubes. Search above and below the expected frequency to find a dramatic dip in SWR. The coupling loop may need adjustment to get the lowest SWR. If the dip is below the 40 M band, withdraw the “trombone” until it resonates at the bottom of the band. If it is too high in frequency with the “trombone” inserted all the way, then there is not enough capacitance. Either the aluminum is not tightly wrapped around the capacitor tubes or the plastic tubes are too short.

Once you are satisfied with the adjustment, mark the copper tubing with a grease pencil to show where the 40 M band is.

Next, pull the “trombone” out a few inches and then find the resonant location for the 30 M band. Finally, do the same for the 20 M band. If your main loop is about 44 inches in diameter, there is a good chance it will work on 17 meters as well.

Using a transmitter and receiver

Use a VERY low power transmitter and an SWR meter. Caution: the currents and voltages around the capacitor section of the antenna are extreme. Even a few watts will cause serious RF burns. Be careful.

Move the “trombone” in fully and then tune around with the receiver until noting a marked increase in noise. This is where the antenna is resonant. Slide the “trombone” until it is resonant at the desired portion of the 40 M band and then apply a small amount of power from the transmitter and check the SWR. If the small loop needs adjusting, turn off the transmitter and cautiously adjust until the antenna is working as desired. Mark the copper tubing to indicate the band.

On The Air

Once you have tuned the antenna to satisfaction, mount it where no one can touch it when transmitting. With a loop diameter of 48 inches, the bandwidth is about 129 kHz on 40 M, and 293 kHz on 20 M. This is wider than many of the commercial MLA’s, but I was more concerned about efficiency and bandwidth. A larger loop is more efficient. A smaller loop can be better at rejecting local noise, but I found the combination here to be more than adequate. A wider bandwidth eliminates constantly re-tuning the antenna.

At a future date, I will post something on how to build a stepper motor driver for this antenna. Look around the Internet for existing designs.

As for maximum power, the antenna has consistently handled 100 watts on CW without heating or voltage breakdown. Since I only tested with 100 watts, it isn’t clear what the upper limit might be.

As for performance, that is a difficult thing to judge. My experience indicates that this antenna on 40 Meters performs almost as well as a G5RV at 35 feet, and as well as the G5RV on the higher bands.

Did the antenna meet the design goals?

My original design goals were modest: the antenna needed to cost under $50.00, operate on three bands, and handle 30 watts. Yes. In fact, it exceeded all the goals, it:

  1. Costs under $20.00 to build (not counting a remote tuning mechanism).

  2. Operates on 40, 30 and 20 M. One version, a slightly smaller loop (44 inches), also functions on 17 M.

  3. Runs well at 100 watts. The upper power limit is yet unproven.

This antenna is impressive. Over the last several months, I have worked many DX stations and maintained reliable communications in long-winded rag-chewing sessions. Not only is it a pleasure to use, it has been a rewarding homebrewing experience.

A 20 meter through 10 meter version of this antenna is possible. I have one where the main loop is 32 inches in diameter (81 cm) and the capacitor tubes are 20 inches (51 cm). The capacitor tubes can use PVC pipe, such as the straight version of the 3/4 inch Sharkbite product and 1/2 inch copper tubing.

73 de K1YPP

Partial parts list

Note: Lowes will ship to store if ordered on line

Item

Quantity

Length

Comments

Charlotte Pipe ¾ inch x 10 ft, 200PSI PVC pipe

1

10 feet

Lowes #23990

Sharkbite PEX flexible tubing

13 feet

Cut short pieces to connect Tee’s Lowes #998500

¾ inch copper tubing, type M

1

5 feet

Confirm it fits in capacitor PVC tubing, Lowes #23792

¾ inch CPVC Tee

2

Sharkbite should fit snugly, Lowes #23760

¾ inch CPVC to PVC adapter

2

Couples Tee to capacitor PVC, Lowes #65322

Aluminum tape, 2 inch x 10 yards

1

30 feet

Plastic backed sticky tape Nashua Corp, #322

Advertisements

2014 in review

December 29, 2014
by

The WordPress.com stats helper monkeys prepared a 2014 annual report for this blog.

Here’s an excerpt:

A San Francisco cable car holds 60 people. This blog was viewed about 590 times in 2014. If it were a cable car, it would take about 10 trips to carry that many people.

Click here to see the complete report.

Rest in peace, Robin Williams

August 14, 2014
by

Robin Williams tragic death produced unprecedented grief. I admit I was very moved by his passing. I didn’t personally know him, but in some ways, maybe I did.

Our relationship was one-way, he talked and I listened. In most relationships, that would be unhealthy, but in ours, it worked. He made me laugh so hard I sometimes had tears in my eyes. Now I have tears in my eyes, and they’re still tears of joy, as tragic as all this is. He made me laugh, I can never forget that.

As I’m getting on in years, I’ve lost many that were dear to me. Many of my buddies from my military duty in the sixties are gone. My first serious girlfriend passed away in 2003. My parents are long gone. My kid brother was killed in Vietnam in ’68. There is a long list of people that I wish were still here. They’re not. I celebrate their lives, they each gave me something.

I loved Robin Williams’ work. However, I don’t think he did. Though he found his fame with his humor, he always wanted to be taken seriously. There were two Robin Williams; the comedian, and the serious actor. In my opinion, I think he wanted to be seen as a dramatic actor. Even though he landed some very serious parts, such as in Good Will Hunting, The Dead Poets Society, and Insomnia, he’s remembered for Patch Adams, Mrs. Doubtfire, Aladdin, Hook and others. For years I’ve observed his trajectory, and he always sought out dramatic work, but the public always loved him more for the humor. It was as if he were the worlds greatest painter, and yet he was known for his electrical engineering work. We, his viewing public could never fully accept him as a dramatic actor. I don’t believe Mr Williams saw himself on a par with the great actors such as Bogart or Brando. It always seemed he viewed his humor as an affliction, rather than a talent. Humor was his ugly twin brother, attached at the hip.

In our day-to-day lives, we tend to pigeon-hole people. I have an author friend, Bill  “Skywalker” Walker, that is extremely tall, about seven feet. I don’t believe a day of his life has gone by where someone hasn’t asked him if he is a basketball player. He has no interest in basketball, but loves golf. He recently wrote an excellent book on the topic, Tall Tales: The great talisman of height.  Similarly, I imagine that not a day of Robin Williams’ life went by where he wasn’t expected to be funny. I think Robin Williams was pigeon-holed as a comedian when all he wanted to be was a dramatic actor. I can only guess here, as I said at the beginning, we didn’t really know each other.

I’ve known my share of writers that have a similar dilemma, they write great non-fiction, but really want to write novels. Dave Berry is a great example. He has dozens of humorous books and has taken a stab at a few novels, but they’ve gone nowhere. How many of us have very successful lives in one field, but wish we were something else?

We, Williams fans, wanted more humor, and he wanted more ‘serious’. His depression amplified his frustration and he is no longer with us. We didn’t betray him, we just didn’t understand this illness that is depression. Apparently, even those closest to him didn’t.

Heart-bypass patients face serious depression issues following the surgery. After my six-artery bypass, in 2007, I was fortunate: no depression. In my therapy sessions I was surrounded by people that were having serious issues. I delved into this in chapter six of my first book, Three Hundred Zeroes. It was my hope that the book would find its way into the hands of bypass patients. I often wonder, with the many thousands of copies now out there, how many readers have undergone bypass surgery. Most don’t realize it, but Robin Williams was a heart surgery patient as well. Could it have added to his depression problems?

Robin-Williams-bypass-scar-1

Robin Williams showing off his heart surgery scar.

There may never be another Robin Williams, he truly was unique. He had a mind like no other. Rest in peace Robin Williams, you gave us far more than you could ever know.

Need help with depression? Get help, don’t wait, we do care:

Anxiety and Depression Association of America, ADAA

National Suicide Prevention Help Line:

  • 1-800-273-8255 (1-800-273-TALK)

 

 

Kindle book pricing and how the big guys don’t get it.

July 10, 2014
by

I love to read. For some reason, as a young reader, I missed many of the classics. I’ve made up for lost time over the years by “catching up.” Books like The Catcher In The Rye, Of Mice And Men, White Fang and On The Road have been books that I’ve only read in the last twenty years or so. The same goes for movies, I’ve caught up on The African Queen, Casablanca, The Godfather and others in the last few years. How did I miss them? I don’t know, perhaps I just spent so much time outside when I was younger, I just missed them. That is a subject for another time.

Yesterday, I read a news piece on CNN about an author that was gored running with the bulls in Pamplona. Bill Hillmann, author of “Fiesta, How To Survive The Bulls Of  Pamplona.” How ironic. It occurred to me that I had not read anything much by Hemingway recently, so I decided to take a look online and see if I could find his book, “The Sun Also Rises.” I figured that, surely, by now, it must be on Kindle for an inexpensive price, or perhaps, even free. Surely.

The book was published in 1926 and is famous for its depiction of running with the bulls. I started hunting around the Internet for a copy. Much to my surprise, actually, I wasn’t that surprised, the cheapest “legal” copy I could find was $7.99, for the Kindle. I could also get a paperback copy for $8.48. The publisher is Simon and Schuster and they, as well as all of the other surviving publishers, don’t “get it.” I’m not going to pay that much for a book written in 1926, I’m just not.

There are illegal means to get a copy, the bit torrent servers have it out there, but I like to do my reading legally. Yes, there is some cost to putting the Kindle version online and I’d willingly pay, perhaps, $0.99-$1.99 for a copy, but $7.99…no way. This problem exists industry-wide. Any of the better known contemporary or classic authors that are still published by the larger publishing houses do this and they’re losing money.

Eventually, I found a print copy in our local library and rode my bike over and picked it up. It is a very old copy, but that’s okay, it is an old book. The publishers lost another sale of an e-book. I wonder how long it will be before they catch on?

Please do comment. Am I being weird or a curmudgeon? How much are you willing to pay for e-books?

Preaching to the choir.

March 13, 2014

Preaching

Sometimes, preaching to the choir can be productive. Last night, I gave a presentation at our local authors club, The Authors Connection. This club was instrumental in getting my book published. The club was formed by Susan Klaus and is going strong. Susan’s latest work is Secretariat Reborn. If you’re a thriller reader, check it out.

My book came to be published because a speaker at the club, Ron Klein, did a presentation about using Createspace.com to publish your book. I was hooked. In no time at all, my book was in print, and the rest was history. It was my turn to “give back,” to the club.

I talked about book trailers. As I’ve noted many times before, on this blog, I detest most book trailers  (Jan 16, 2012 and Jun 30, 2011). It isn’t that I dislike trailers, I just dislike how many of them totally suck. The presentation last night was intended to show a few good ones and show the members how to create a “low budget” yet effective trailer. The intent wasn’t to show the authors things that they could mimic. The purpose was to give them ideas. They’re creative people, most of them will come up with something even better.

The very first thing I did in the meeting, was record a short two-minute book trailer. It was the simplest kind: an author talking to the camera. I chose discussing why the reader should read Three Hundred Zeroes. The purpose wasn’t so much to make a trailer as it was to demonstrate how to record the video, put it on the computer, and then upload it to Youtube.com. Filming this live was a gamble. A slow link could take 15-20 minutes, but fortunately, it only took about a minute. My fallback plan was to start the upload, and then play a few favorite book trailers while we waited. I didn’t have to.

The pressure was on me, as the presenter, to nail the video correctly, the first time. There was no time to do a retake. Luckily, it went well, although my trailer was a little “stiff.” You can see it here: 

 

Prior to the meeting, I posted the notes at: Book Trailers for Sarasota Authors Connection. My intention was to give the audience an interactive page where they could view the trailers in more detail and my comments on why I chose those trailers. This eliminates their having to take notes and get web addresses incorrectly. Following the meeting, I included a link to the book trailer we did on location (which I obviously had to add later!).

I cannot attest to the quality of any of the books, I was merely interested in their trailers. They all had something that I liked about them, but perhaps not everything. Look that page over, watch some of the trailers and let me know what you think. Do you agree, or disagree? Do you know of a book trailer that you REALLY like or dislike? Post a comment, we’d like to hear from you.

Photo is Creative Commons, courtesy of Boston Library.

The fine print in writing contest submittals.

February 5, 2014
by
The Trader: Man With No Face, by RK Mann

The Trader: Man With No Face, by RK Mann

Rachel Mann, a local Florida author, is our guest blogger today. Rachel authors Sci-Fi thrillers. Her latest, The Trader: Man With No Face, reminds me of the George Lucas Star Wars series. 
 
Today, Rachel offers up information and cautions on getting involved with publishing contests. She specifically investigates the Amazon Novel Contest. 
___________________________________________
 
Amazon has a novel contest for works that have not been published or have been self published. Submissions begin in February, 2014. You can view the terms at:
 
 
I read the terms and  the only prizes seem to be reviews in Amazon and (at the top) Publisher’s Weekly, plus Amazon publishing contracts. I was floored by what I found in the fine print. Look closely at section 5. Grant of Rights: 
 
you agree to negotiate the terms and conditions of a publishing agreement exclusively with Amazon Publishing for a period of 30 days after you receive notification from Amazon Publishing. If you and Amazon Publishing have not reached agreement after 30 days, you may offer the work to other publishers on the condition that before you enter into an agreement with another publisher, you will afford Amazon Publishing the last right to publish your Entry on the same terms and conditions offered by any other publisher, plus an advance against royalties 10% greater than the other offer… 
 
then check out section 9. Prizes:
 
…Amazon Publishing will determine the royalty rates to be paid under the publishing contract. If you are the Grand Prize Winner, you may not negotiate the publishing contract with Amazon Publishing, and you must sign it “as is” upon receipt of the executable contract (as described in Section 11 below) if you wish to enter into the publishing contract being awarded… 
 
The same applies to the first place winners.  If you read the posted contract details they don’t reveal much except the advance.Though they say in section 5. you can negotiate, in section 9. they say you cannot. Worse,  if you decline their deal, they have the right of first refusal – their terms being you must submit another publisher’s contract and they may match the contract and increase the royalty by 10%.  
In other words, if you don’t do their unknown deal, you will be negotiating in bad faith with anyone else. And since this contest is probably well known and Amazon’s terms are posted on the web, other publishers will know about it. Thus, why would any other publisher bother to even offer a contract, since they would know Amazon has the right to top it? Amazon claims the option to offer you a publishing deal, even if you don’t win, and bind you by the same first right of refusal. 
As I read it, Amazon can prevent you from ever getting another publishing deal on your work by just entering their contest. And they haven’t even paid you a dime. 
Of course, if you don’t care about your copyright, other rights to your work (film, tv, etc.), sequels and royalty rates, Amazon will give you a cash advance and reviews (presumably good) if you win. 
 
– Rachel Mann
___________________________________________

 Thoughts? Comments? Have you ever entered a contest? Did you win, or place? How was your experience?

Some pointers on publishing in 2014

January 9, 2014
by

As is obvious, I’ve been absent from this blog for some time now. Being a “one-man show,” there is only so much time in the day to accomplish things. I believe that most modern-day authors, well know this. Some things have to give way to higher priority items. I gave a speech, about a year ago, on the state of publishing today, and what it means to aspiring authors. Here is a video of that speech. It is about twenty-minutes long and sums things up pretty well. Get a cup or tea, or coffee, sit down and enjoy…

%d bloggers like this: