Antenna on the 40m band with low height of suspension
This is the simple “Delta Loop” Antenna on the 40m band with low height of suspension. Its upper corner located at the height of λ/4.
I.e. for this antenna acceptable any mast with height approx. 10 meters. Feed line connects to any lower corner into break of a loop.
With such design, this antenna has a big radiation level of vertical polarized wave, with small radiation angle, equal 25-35°. So this antenna is suitable for DX QSO.
The optimal dimensions of this wire antenna shown on the figure below.
The input impedance of this antenna, measured on 7.02 MHz, equal 160 Ohm, therefore for optimal matching with 75-Ohm TX used matching device from coaxial cable. For creating such matching device it is necessary two serial connected λ/4 transformers (75 Ohm and 50 Ohm).
The input impedance of antenna on first stage is converting to 35 Ohm, then to 75 Ohm. SWR in this case not more than 1.2. If “Delta Loop” installed at the distance more then 10-14 m from TX, then to points 1 and 2 it is possible connect coaxial cable with wave impedance 75 Ohm with needed length.
Shown dimensions λ/4 transformers correct for cables with the velocity factor equal 0.66. Antenna was tested with 8W QRP TX. With Delta Loop antenna, constructed as was mentioned above, were made CW QSO with VK, ZL, EU, and this confirming the effective of this antenna for working with DX stations.