Delta Loop for the 20m band

A delta loop antenna is not particularly suitable for SOTA. It requires much more space than a vertical and the set-up is more complex.
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.
If you are looking for a delta loop for the 40 metre band, try this Link.
A possible application could be the VK/ZL/JA <> EU S2S event or the Trans- Atlantic S2S QSO party.

During our DX-pedition (Link) to the Principality of Liechtenstein in Sept. 2013. DL4AAE worked hundreds of JA’s on 20 metres with this antenna and 100 W output power.

Delta Loop on HB0/Li-004, Augstenberg, 2359m a.s.l.

Design:

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 = 2,0 m
h   = 4,0 m
a   = 0.7 m
x   = 4.88 m
U   = 22.5 m (Umfang/circumference)

The circumference has been calculated for a wire with an inner diameter of approx. 1.6 mm (conductor) and an outer diameter of 3 mm (insulating material PVC).

Support:

The shown design requires a pole of just six metres height. A six- metre squid pole is not recommended however, because the top segment is way too thin. We use a ten metre pole from DX-wire instead. Not used segments can been removed to reduce weight.
The wire runs loosely through an insulator at the top. This allows the Delta Loop to be easily aligned symmetrically.

Feeding:

As shown in the picture above, this design can be fed with 50 Ohm coaxial cable and requires neither BALUN nor matching.
Make sure the coax runs perpendicular to the plane of the loop. It musn’t touch the antenna wire!

Details:

Feed point with pull relief (not weather-proof but acceptable for most activations).

Lower left/ right corner of the delta loop with fixed insulator.

Performance:

The bandwidth of this design is huge. If tuned to 14.175 kHz, it will cover both, the CW- and SSB- portion of the 20 metre band.

SWR plot of the delta loop tuned at 14.050 kHz

The calculated gain is 3.5 dBi. Thanks to the mostly vertical polarisation, the vertical take off angle is only approx. 20° and doesn’t change much with ground properties.

Vertical radiation pattern (chart normalised to 3.5dBi)

The horizontal radiation pattern is nearly omnidirectional with its maximum perpendicular to the broad side of the loop.

Horizontal radiation pattern (chart normalised to 3.5dBi). The loop runs in 90°/270° direction.

Conclusion:

The new design of the delta loop has several advantages:

• impedance approx. 50 Ohms, thus no matching required
• feeding with coaxial cable is possible, no BALUN required
• large bandwidth
• low take- off angle
• ground properties have little impact on take- off angle

It could be worth trying on a summit…

All credits go to DL4AAE.