There are different systems to make a 40-meter antenna compact-sized,
the most commonly used system is certainly the use of coils, but linear loading is also very popular.
The positive aspects are:
lightweight antenna with compact dimensions!
The negative aspects are:
limited bandwidth and reduced performance.
Momobeam’s construction philosophy does not contemplate the use of coils and has introduced in its multiband/monoband models a modified version of the model invented by Mr. Dave Leeson, W6NL, which I had the honour to meet during the Friedrichshafen fair in 2017 (thank you Mr. Dave for your work)!
This is a variant of the moxon rectangle that allows a reduction in physical size of around 30% without compromising performance. In essence, it is a compact antenna but with full size performance!
As evidence of this, the bandwidth of this antenna is about 300 KHz with SWR under 1:1.5!
At the feed point we have to connect a 50 Ohm cable without interposing any adapting systems, which often make the system metereopathic and very susceptible to high powers! Obviously a 1:1 balun is strongly recommended but not indispensable and can be replaced with an RF Choke made of coaxial cable.
The positive aspects are:
efficient antenna with a large bandwidth and no critical elements (hairpin, gamma match or other adaptive systems) that can be damaged by high powers or moisture etc.
The negative aspects are:
Not exactly small dimensions, and a few extra kilos of aluminium!
This solution is adopted in our two-element 40 monoband version MONO2 40T and multiband version TETRA14, TETRA15 and TETRA18.
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