Wednesday, March 23, 2016

HALO Antenna Homebrew

Source: KR1ST

Build instructions for a 2 Meter HALO antenna for omnidirectional ssb and digital modes horizontally polarized.

Source: KP4MD

Another set of 2 Meter HALO build instructions.

Source: N6TWW

Formulas for calculation of element length is wavelength divided by two (half wavelength) at about 98% efficiency of light speed.

The speed of light is approximately 186000 miles per second in free space.

5280 feet per mile

186000 miles X 5280 feet = 982080000 feet traveled in one second by the target frequency

144.250MHz is a center frequency for SSB on 2M

982080000/144250000 = 6.8 feet

6.8 feet X 12 inches = 81.6 inches).

81.6 inches is how long one wave length is at 144.250MHz.

propagation velocity through the element is maybe 98% the speed of light.

81.6" X .98 = 79.97"

The loop is 1/2 wave length

80"/ 2 to arrive at 40" length of the element.

2 Meter: 982080000/144250000*12/2*.98 = 40.0320998267 inches

These same formulas can be extrapolated for other bands such as:

6 Meter 50.02 MHz: 982080000/50020000*12/2*.98
115.446429428 inches = 9.62053578569 feet = 2.932 meters

1.25 Meter 222.125 MHz: 982080000/222125000*12/2*.98 25.9972105796 inches

70cm 432.05 MHz:982080000/432050000*12/2*.98 = 13.3656530494 inches

Source: KR1ST

With the addition of a phasing harness it is possible to stack HALOs for greater gain.

PROTOTYPE:

This photo is a prototype of an adjustable HALO for multiple bands. I am hoping that this can be resonant and 1:1 SWR in the calling frequencies for most digital modes.

I plan to carry this plus a small SDR and maybe transverters in my carry-on bag with clothes for 7 days. It must perform well for weak signals on the 2M, 1.25M and 70cm bands. 

I think that 6M and HF bands could also be possible with sections of copper pipe less than 19" and/or loading coils. It will be interesting to see how tunable it can be by screwing in more or less sections and components.