Up until the past decade or so, there were only two types of multi-band Yagis for HF: the traditional 3- or 4-element triband designs with traps or the physically larger & heavier trapless Log-Yagi with continuous 10-30 MHz coverage.
Today, there are antennas from several manufacturers in which these designs have merged, combining a 3-band trapless Yagi into a triband-sized footprint, weight and wind load.
In addition to a lack of traps, these Yagis are characterized by closely spaced elements and (in at least two cases) by separate driven elements for each band. Regardless of having separate driven elements only one feedline is used, with the RF being coupled into the “parasitically driven” elements via the directly-driven element for 20 meters (Force 12 C3).
So the new designs are smaller and lighter than Log-Yagis without the traps of traditional tribanders.
Reviews of these antenna types are universally positive however few of the reviewers mention what antenna they had prior to one of the new designs.
Examples of this antenna type are:
- Cycle 24′s TX38 (pictured above)
- Force 12′s C-Series
- Cushcraft’s X7 (with traps only in one of the driven elements)
- OptiBeam (several designs)
With there being no such thing as a free lunch, what was given up to allow a trapless design without the huge footprint of a Log?
Continuous coverage, for one and (from what I’ve read so far) a decreased front to back ratio compared to a trapped Yagi. Forward gain appears to remain the same.