Yagi matching.

Last night, I set about getting a 3-element, OWL Yagi from Innovantennas (50MHz) up in the air, simply to get it matched-up properly; sadly, this is not a location for permanent installations (I'm already very fed-up of this and putting the house for sale next week, after only a few months here).

The antenna was designed for rear-mounting, but I decided to try it horizontally for inland-based operation (vertical is infinitely better at the coast).

5-ele version of the 50MHz OWL from Innovantennas. Sturdy, just not very practical for /p; the rear mount of the 3, let alone the 5-ele, also places large, impractical leverage stresses on the boom.

 

The matching using the published element dimensions didn't work out too well, in either horizontal or vertical orientation. Although the lowest point in the curve was broadly in the correct place (~50.25MHz), the SWR at that point was about 1.48:1 when horizontally-mounted. Not the end of the world, but we can do better than that when, at the SSB and FT8 calling frequencies, the SWR was over 1.5:1.

My antenna initially exhibited this type of fairly high-SWR matching, showing the element lengths weren't right.

I didn't think the recommended reflector dimension was long enough; it was essentially the same length as the radiator loop. I increased this by about 2cm per side, and immediately, the matching improved to about 1.38:1. 

I then tried increasing the length of the director elements by about 1cm each side. Again, this had the desired result, bringing the matching to 1.18:1 from 50.150 to 50.320 MHz - SSB and digital portions now perfect!  I'm sure I could bring it a bit lower, but it isn't really necessary.

So, good matching for the OWL antenna, with not too much fuss. I can't say I'm overly-impressed by the antenna in general, though. I don't like having to jam a screwdriver into a hole as the designed way of tightening a through-boom element nut!  The quality of the build instructions is also quite poor, with a very hurried, error-prone feel to it all. Quite disappointed, overall, but it was cheap enough (£89). With the director and reflector removed from the boom, and the outer elements of the radiating loop also, it does fit without too much fuss in a typical family hatchback.

I'm currently building a Moxon to replace this antenna for /p use. In fairness, the Moxon will likely work out about the same price as the Yagi, all things considered, and it also a bit of a transportation nuisance!