A delta loop antenna is not particularly suitable for SOTA. It requires much more space than a vertical and the set-up is more complicated.
Nevertheless I’d like to show this design here because sometimes space (and weight) don’t matter and a low take off angle is welcome. One possible scenario could be the VK/ZL/JA <> EU S2S event.
Uwe, DL4AAE, ran various simulations in order to optimize the „classical“ delta loop design. He summarized the results in an excellent presentation here (German only). Based on his design I built the following delta loop:
Dimensions (optimized for 14.050 kHz):
h0 = 2,0m
h = 4,0m
a = 0.7m
x = 4.88m
U = 22.5m (Umfang/circumference)
The circumference has been calculated for a wire with an inner diameter of approx. 1.6mm (conductor) and an outer diameter of 3mm (insulating material: PVC).
Some details of the design can be seen below:
Feeding the delta loop with coaxial cable works without BALUN (even though it doesn’t look nice). However, special care has to be taken of the coax: It mustn’t touch the horizontal wire.
The shown design requires a pole of just 6 metres length. However, a 6m pole is not recommended. It won’t withstand the force acting at the top. We use a more robust 10m GRF pole instead. Not used segments can be removed (s. picture above).
The bandwidth of this design is huge. If tuned to 14.175 kHz, it will cover both, the CW- and SSB- portion of the 20m band.
Thanks to the mostly vertical polarisation the vertical take off angle is approx. 20° and doesn’t change much with ground properties.
The horizontal radiation pattern is nearly omnidirectional with its maximum perpendicular to the loop.
The new design of the delta loop has several advantages:
- impedance approx. 50 Ohms, thus no matching required
- feeding with coaxial cable is possible
- large bandwidth
- low take- off angle
- ground properties have little impact on take- off angle
It could be worth trying it on a summit with easy access.