A delta loop antenna – especially for the 40 metre band – is not exactly suitable for SOTA. It is huge and requires a lot of space. Furthermore the set up is time-consuming.
Nevertheless I’d like to show this design here because:
- During sunspot minimum 40 m still offers the opportunity to work a lot of DX.
- The delta loop provides the required take off angle to work the DX.
- Sometimes space (and time) don’t matter.
- It’s fun building it 😉
A possible application could be intercontinental S2S events.
Here is the Link to the 20 metre version of the delta loop.
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.
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 7.030 kHz):
h0 = 2.0 m
h = 7.6 m
a = 1.2 m
x = 9.715 m
U = 44.1 m (Umfang/circumference)
The circumference has been calculated with NEC2 for a wire with an inner diameter of approx. 1.6 mm (conductor) and an outer diameter of 3 mm (insulating material PVC).
It’s strongly recommended to leave the wire about 50 cm longer at first and then shorten it bit by bit to reach the desired resonance frequency. In my case 50 cm had to be trimmed. In other words, after carefully tuning the delta loop I ended up with the calculated wire length of 44.1 metres.
The shown design requires a pole of approx. ten metres height. A ten metre squid pole is not recommended however, because the top segment is way too thin. We use the ‚heavy duty‘ 12.5 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 the delta loop:
As can be seen in the pictures 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!
The bandwidth of this design is huge. If tuned to 7.100 kHz, it will cover both, the CW- and SSB- portion of the 40 metre band.
Note: SWR-plot is still missing!
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.
The horizontal radiation pattern is nearly omnidirectional with its maximum perpendicular to the plane of 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, 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.