This is a design I’ve just completed after much alteration to get the best front to back (F/B) ratio whilst keeping the forward gain as high as possible.
It’s taken quite a few iterations to get to this point but, I’m hoping it will prove to be a great DX antenna.
The antenna is based around a simple Delta Loop design utilising two elements, one driven and one as a reflector to provide forward gain whilst maximising the F/B ratio.
The reflector element is slightly bigger than the driven element as this improves the F/B ratio considerably. This design doesn’t require a non-inductive resistor in the reflector like my 40m Band 2 Element Delta Loop Beam. This makes the build process considerably easier but, requires more accurate measuring of the wire lengths during build. (I will probably re-visit the 40m band design and remove the resistor and increase the size of the reflector accordingly).
The driven element is separated from the reflector element by 3.6m to maximise F/B ratio and forward gain.
The driven element is fed in one of the lower corners using a 2:1 balun to convert from unbalanced coaxial feed to the balanced loop antenna. Since the antenna presents close to 100 Ohm impedance the 2:1 balun will transform this down to approximately 50 ohms giving an excellent SWR of less than 1.5:1 across the whole band.
The driven element has a horizontal wire length of 7.69m long exactly 1m above the ground. The two diagonal wires are 4.876m long with the peak at 4m above the ground.
The reflector element is slightly bigger than the driven element with the horizontal wire being 7.9m long at exactly 1m above the ground and the two diagonal wires being 4.96m long with the peak again at 4m above ground.
The 3D field plot shows a really nice front to back ratio with a fairly wide forward gain lobe.
The 2D elevation field plot shows a forward gain of 9.64dBi at 10 degrees and 18.37dB F/B ratio.
With a nice low angle of maximum radiation this antenna should be good for the long haul contact on the 17m Band.
I’ve now ordered a 240-43 Ferrite Toroid from HAM Goodies to make the 2:1 Balun and will start construction once it arrives.
I’ll update this page with details of the build and results as I go.
Summary:
Driven Element
Horizontal Wire Length: 7.69m @ 1m above ground
Diagonal Wire Lengths: 4.876m
Height at Centre: 4m
Wire Dia: 2.5mm
Feed Type: 2:1 Balun in bottom corner
Impedance: 50 Ohm
SWR: <1.5:1 across entire band
Reflector Element
Horizontal Wire Length: 7.9m @ 1m above ground
Diagonal Wire Lengths: 4.96m
Wire Dia: 2.5mm
Height at Centre: 4m
Distance between Elements: 3.6m
Gain: 9.64dBi at 10 Degrees
F/B: 18.37dB