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.
