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Multiband Maypole HF Antenna The Maypole
Antenna Traditional Definition of the Maypole: A tall pole with long ribbons (= narrow strips of cloth) fixed to the top of it, the ends of which people hold as people dance around the pole on the first of May. Ham Radio
Definition of a Maypole
Antenna:
A tall
single mast supporting several dipole antennas arranged in a pattern as
viewed from above in many directions. Hams substitute the ribbons with
dipoles! We do not hold them but we do dance when they get out a better
signal for our ham
station!
The multiband HF Maypole antenna is a spin off of the fan dipole that was "invented" many years ago by an unknown ham radio operator who wanted a multiband dipole antenna "system" to cover more than one ham band and fed with a single length of coaxial cable. So rather than have several dipoles suspended under each other that sometimes were very difficult to tune for lowest swr, due to interaction between them, the idea came about to spread out the dipoles in many directions from a single support mast. In the multiband HF Maypole antenna, each operating
band is chosen such as the 80, 40, 20 and 10 meter bands as separate
dipole antennas all connected to one single coax feed line at the highest
point on the support mast. In other words, the dipoles are in
parallel with each other at the feed point at the top of the mast and then
arranged in a more or less circular pattern spreading out in many
directions on the compass. It looks complicated but not really! It's just a few dipoles all connected together at one common feed point. The only important thing is that you must have the horizontal room for the longest dipole which would be the lowest frequency band of operation so plan in advance. Each dipole is designed for the band of your choice using the standard formula for half wave dipoles. Then the other dipoles for other bands that you design are connected to the same feed point, all dipoles in parallel with the others. All of the separate dipoles are arranged in an inverted V fashion much like the real Maypole and the angle is not critical. At the central coax feed point at the top of the
support mast, one half of each dipole is connected to the coax shield and
the other half of each dipole is connected to the center conductor. This
makes them parallel with each other. Since there are many methods to make
these connections, use your ham engineering here. By arranging the dipoles in many different directions from the mast support, this helps to prevent any interaction between them which may make swr tuning more tedious if you used the "fan dipole arrangement". After the Maypole antenna arrangement is in the air, you can check the swr on each band for low swr. An acceptable swr would be at or near a 1:5 to 1 ratio or at least no higher than about 2:1. If you are a purest and want to go to the trouble of tuning each dipole lower than 1:5 to 1, then that is your choice, but if you have an antenna matcher, (tuner), just use it to peak and tweek it as needed and then remember your tuner settings for each band.
Important! Added
notes:
1. Seal all of your connections from
mother nature, especially the end of the coax at the feed
point.
2. Each end of the dipole must have an
insulator of your choosing and then tied off to the end supports. Each
dipole then becomes its own guying
system.
3. A 1:1 choke/center insulator is
recommended to help prevent feed line
radiation.
4. Guys for the mast
MUST NOT be conductive. Do not use metal guy
wires!
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