A Mississippi Style 40 Meter Magnetic Loop
Ken Holland, K9FV
Edited by Brian Levy, W2BRI
It all starts with my friend Leon, K5BUL. Well, he’s a new ham of about 3 years who lives in Aberdeen, MS. He got into ham radio because he wanted to use it as part of cruising on his 35â€™ Fantasia sailboat. His life took a different turn after he bought a new â€™99 Goldwing motorcycle. Heâ€™s now a biker. He has even mounted a screwdriver antenna to his bike and has worked HF using his ICOM 706MKIIG on the motorcycle.
Iâ€™ve myself have been a ham since the mid-70â€™s (â€™75 I think) with the original call of WA4UBD, which I kept until a couple of years ago when I got the vanity call K9FV. Iâ€™ve used ham radio on my sailboat for years. In â€™99 when the XYL and I took an extended honeymoon for 6 months to the Bahamian Islands, ham radio stood us in good stead.
We had been in the Islands only a few weeks when Hurricane Dennis decided to visit. We found a protected place and rode out the hurricane. The first night out after Dennis, we headed out of the cove. We decided we wanted some something good for supper so we dove for lobsters. What was most unfortunate, however, is that while I was cleaning lobster, my XYL took a shower, slipped, and broke her pelvic bone! The next morning as the Intercoastal Waterway Net came on I reported my emergency traffic. Dr Jim of Miami came on the air and discussed my wife’s symptoms with me. We agreed that it did in fact sound like a broken bone, and she would surely need more medical attention. Needless to say, we needed more medical support than the island could provide. Another ham got on the air and did a phone patch, we were still anchored out, to my insurance company and to DAN (Divers Alert Network). I then upped anchor to the closest marina where we could access the island’s nurse and a pay phone. DANâ€™s staff doctor talked to the local nurse at the island, then the DAN doctor talked to my insurance company. The insurance company authorized a Lear jet ambulance to transport us to Fort Lauderdale for medical treatment.
Since that fateful experience, my XLY does not complain about any radio purchases I make. These days I just say â€œItâ€™s for safety on the boatâ€. She even bothered getting her Technician license â€“ KG4TIN.
From time to time, I also install a screwdriver antenna on my motorcycle. It’s an old â€™92 goldwing and it works just fine for HF mobile.
Let’s get back to the topic of Magnetic Loops. Leon and I both share an enjoyment for building things, and antennas are certainly included. Since I live on a 40â€™ sailboat, and he has the land for antennas â€“ we do most of our antenna work at his QTH. After reading Brainâ€™s post (W2BRI) on QRZ and eham.net, I visited his webpage and liked what I read. I spoke to Leon and sold him on the idea of a magnetic antenna before Christmas of 2002. By Christmas Leon had the basic loop built using electrical 3 inch aluminum conduit. This is a fairly heavy walled soft aluminum pipe that bends easy. Leon constructed the loop using â€œfactory 90â€™s.â€ These are pre threaded pipe which is bent into a 90 degree pieces. The loop is a 10 foot by 10 foot square with a 3 inch gap at the top of one side â€“ like we saw in Brian’s antenna plans on this site.
Leon and I got the Magnetic loop tuned and tested Dec 30th, 2002. Leon had the loop all made up and ready to be completed when I got there on Monday morning. We hung the 10 ft square loop from a tree limb putting the bottom about three feet off the ground. We added the feed and the capacitor and got the loop tuned up to forty meters.
We turned on the radio, and got ready to do our on the air comparison. We were located just north of Columbus, MS. We were able to test the antenna with a station in Talladega, Alabama against Leon’s permanent forty meter full wave loop at 30 feet. The gentleman in Talladega was located about 200 miles ESE of our location. WA4FMR near Knoxsville, TN was our second contact, who was located perhaps 400 miles NE of us. Both stations gave good reports on the magnetic loop, but did say the full wave 40 meter loop was better by about 1 or 2 S units. That was about the same results we saw on the S-meter when receiving the two test stations. This performance confirms what Brian had expressed to me earlier on the phone. The one major advantage with the loop however, is its small size. Leon liked the loop so much, he is now planning a 20 meter version. He hopes to compare it to his 20 meter bazooka one day.
Ken Holland, K9FV