ADS-B antenna and stats – Antenna Y1

This is a work-in-progress and relates to this article on further developments beyond the details below.

As a result of my inability to stop messing with new ideas I’ve deviated (hopefully only temporarily) from the plan to make minor, iterative alterations to a basically-similar antenna design in order to establish the effectiveness of each individual feature or component. The deviation is to build a first (and basic) Yagi-Uda antenna to see a) whether or not I can make something work, b) whether it has any advantages (I’m hoping for extended range but reduced “angle-of-view” – I know there’s a technical term but I’m still such a novice I’d rather not confuse these notes by using the wrong term incorrectly), and c) whether I can learn a bit more about a bit more.

So, the design is a basic Yagi antenna with 8 directors, a reflector and a folded dipole as the driven element. It uses RG-58U (50Ω, 0.66 velocity factor) coax as a feedline and the same cable to construct a balun. The directors and reflector are mounted on a plastic conduit as a boom by feeding them directly through it and the dipole is mounted using a 3D-printed “bracket”.

This page is still being updated so will contain more design notes and more performance notes over the coming days and weeks (currently late November 2021).

Useful – www.antenna-theory.com

Indispensable – https://www.vk5dj.com/yagi.html

To add…output from calculator, photos of construction and finished initial design.

Performance with this antenna, has been very interesting. It immediately performed considerably better than I expected.

A few notes that interested me but may be of no surprise to others with some experience:

• It appears that mounting it close to the already-operational collinear antenna renders the collinear slightly directional (ie less than the seemingly omnidirectional antenna it has been). This needs further testing.
• It doesn’t cope particularly well with movement (or at least the FlightAware stick doesn’t cope with the changing signal produced when moving the antenna). Rather than performance changing as it is moved, as happens with the collinears, it gives up, freezes and then appears to sort-of “reset” and start again once it is static for a while. This is more pronounced with rotations along the axis of the boom – ie turning the antenna so that the dipole is vertical instead of horizontal, or with angling the boom to point more upwards or more downwards – ie pointing it to the sky or to the ground. Changing the bearing has less effect but a major move has a similar impact – ie moving from SW to W.
• The antenna appears to perform considerably better in all respects when mounted with the dipole vertically.
• Performance (at least in terms of messages/sec and, therefore I would assume, all other measures) can be tweaked by sliding the dipole to-and-fro from the reflector. I assume there will be other tweaks that adjust performance but this is the easiest for me to achieve with this design and the first adjustment I stumbled upon.

Initial (first half-hour) findings are that performance is similar to the collinear Antenna B & C, albeit with that antenna mounted very nearby. Non-analytical comparisons seemed to suggest that antenna C had been affected by the introduction of the Yagi so, when they are separated by a bit of space that might change. Or it may be that I was persuading myself of that by doing it late at night when I don’t usually look at figures and that they are lower than I was expecting anyway – not a like-for-like comparison just at this time.

[A few days later] I’ve moved antenna C to a position about 500mm away from it’s original position so there’s now no point of the Yagi Y1 within 500mm of C. Performance immediately changed – it looks more like itself in terms of its omnidirectional qualities and also in terms of its range. So I’ll leave them like this for a while and monitor some more. Probably then I’ll go back to comparing collinears to fine-tune those, and do similarly in a few months with two Yagi’s.

See here for its inclusion in the usual stats comparison.