162 MHz Yagi Antenna (λ = 1.85 metre)

I have fabricated and tested; a 5 element Yagi "cut" for 162MHz.(vertical polarization).
This is used to receive AIS data signals from ships at sea.
For construction: I recycle, dismantled Hills Australian brand domestic TV aerials.
For equal size and weight a YAGI should deliver, greater directivity and power gain
than other antenna designs of equal complexity.
This is a scaled version of a well proven DK7ZB 144MHz design.


The easiest yagi-aerial to fabricate is what Americans call "plumbers delight" construction,
i.e. an array constructed entirely of metal, with no insulating members needed between the elements and the supporting structure.
The driven-element (gamma-match feed) can also be directly affixed to the boom.
To evaluate the antenna, I excited it with a 25 watt marine radio {@ 162MHz} and measured VSWR (voltage standing wave ratio) with a reflectometer, and tuned accordingly (tap point and var' Cap').
In testing I also tried the sleeve balun Z matching method (which I had used in other builds),
but couldn't obtain an acceptably low VSWR
However by using the well known Gamma Γ match I was able to acheive an SWR of 1:1



GAMMA MATCH ( Γ )
I presume the Gamma-Match gets its name from the similarity of the tuning bar and tap-off point,
to the Greek capital letter gamma ( Γ )

References:-
1) VHF Handbook for Radio Amateurs.Herb Brier W9EGQ & William Orr W6SAI 1984 pg 241
2) The Radio Handbook 14th Ed. Editors and Engineers (William Orr) 1956 pg 429



A (pF) B (cm) C (cm)
Frequency {MHz} Dipole Length
0.471 λ (mm)
E&E OrrE&E
10%
Orr
14%
E&E
1.43%
Orr
2%
144 978 13.7 20 9.8 14 1.4 2
162 872 12 17.5 8.7 12 1.2 1.75

E&E gives capacitor value as 7pF per metre of wavelength (λ)

This tuned-up aerial should then perform good for reception, showing sensitivity and directivity!
I acknowledge my interest in AIS was aroused mainly because of the efforts of :- VK2KRR