The Maypole Antenna

For those of you that are curious, I hope this article will shed adequate light on one of the most effective and efficient antennas I've ever had the pleasure of building, experimenting with, operating with, and preaching the virtues of.

What is a Maypole antenna?

A maypole antenna is any 2 or more inverted V's, all connected to a common feed point, then evenly spread out over a 360 degree circle. Picture the frame of an umbrella, if viewed from overhead. Coax feed the antenna platform to the transceiver with 50 ohm coax. There is little or no need for antenna tuner assistance, especially on those bands with resonant wire representation. In other words, if a Maypole antenna is constructed to have 75/40/20 meters, there will be nearly a 1 to 1 match at some frequency point, on all 3 bands. The math necessary to calculate the wire lengths is the same math necessary for calculating a dipole; 468 divided by the target frequency will yield the overall wire footage necessary for each antenna for the maypole. This figure then is divided by 2, as each leg of the inverted V, will be cut to this figure, or 234 divided by the frequency. Also keep in mind, 15 meters will be represented in a 3/4 wave fashion, as long as there's a 40 meter inverted V, present on the platform. An antenna tuner will be necessary for operating on this band, as a 2 to 1 VSWR will be about the best you can get with the direct connection.

Why a Maypole?

Pure and simply, why not. Any antenna that can perform efficiently at full legal limit, without mandatory tuner assistance, and provide excellent omni-directional pattern coverage, should appeal to everyone from field day'ers, hunters, campers, and of course, emergency responders.

Design suggestions for the Maypole

I've built many Maypole antennas over the years, with many different band combinations, presented at the feed platform. One suggestion I encourage, is that you never allow less than a 32 degree separation, between antenna wires. In other words, a 75/40/20 meter Maypole, will have 60 degrees between all antenna wires, if put up correctly. A 75/40/20/10 meter Maypole will have 45 degrees between antenna wires. May I suggest using traps, if additional bands are desired. This approach also allows complex Maypole designs to be placed in smaller areas, where less than desired space is available.

How high should the Maypole platform be?

Perhaps the question I've been asked, the most. The answer depends on the lowest band antenna desired on the platform. If 40 meters is the lowest band desired, 28 feet high, will work fine. Should you want 75 meters to be the lowest band present, I recommend at least 35 feet high, or more. Should you desire 160 meters, the fed point now needs to be at least 60 feet high, but 80 feet up, would definitely perform better, with a more omni directional pattern resulting on 160 meters. You do not need to have perfect 45 degree angles from the pole to each wire. However, having angles greater than 60 degrees, will allow the antenna to perform in a bi-directional pattern, as well as raise the feed point impedance slightly. I recommend that terminating insulators be about 5 feet above the ground for the safety of those that may be wondering in the area below. I also do not recommend baluns as part of the antenna feed system, unless bands other than those present on the platform are desired to be operated on. Only then would I suggest a Maxwell type current balun, but not at the platform fed point. A current balun placed closer to the radio/tuner setup will better strip the skin currents that will be present.

The materials I recommend for building the Maypole, as well as construction of key antenna parts, appear in subsequent articles on this web site.

Please feel free to contact me with any questions, as I'm sure there will be some, I've failed to address.

Mark
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