The antenna strategy focuses on simple and reliable resonant vertical antennas.
On 80, 40, and 30m RX-Beverages are foreseen, perhaps some loops.
4NEC2 is used to design the antennas and simulate/forecast their behavior ‘on site’.

Eucalyptus and/or bamboo poles (the higher the better) are envisaged as antenna masts.

80m: T-antenna (12 – 15m high) with sloping top loads matched against Zp (‘Y’).
Either strips of chicken fence (said to be ‘available’) or resonant elevated radials
serve as ground system. Note: 80m was not activated during this trip.

40m: Deltaloop (fed ~¼λ from the apex) or a ¼λ vertical with at least
two elevated radials (preferably more).

30m: Vertical dipole array (VDA) when the poles are high enough, otherwise a deltaloop.

Advantages of a deltaloop are: minimum of material, no critical ground system, can be forced towards Z = 200 + j0 Ω to obtain a (broad band) match with a 4:1-balun, good radiation pattern (take off angle is a few degrees lower than a ¼λ vertical above same ground), and very simple (mechanical) construction.
Having built several 40m deltaloops in various places/conditions before, this antenna works very well for DX and is built within no time.

Below a ¼λ vertical with 4 elevated resonant radials and a properly fed deltaloop above identical ground are modelled. (click on image to enlarge)

20 – 10m: Vertical dipoles arrays for each band (click on images below to enlarge in new tabs).
DSCN9989a  DSCN9563c

6m: Many requests for 50 MHz have been received.
To manage expectations in advance: if… I’m able to build a Yagi, I give it a try.
Hartmut DG7YBN, kindly designed a non critical 5el.Yagi especially for me : -)
Note: due to lack of propagation not activated during this trip.

RX-Beverages (depending on the QRN) are foreseen.
Negotiated lengths are 80m (2λ @40m) as the local population feared the wires
running in the field, and in/next/through to their village.
Will experiment there with ‘open Bevs’ (‘bi directional’) or terminate them,
provided there’s enough space to compensate ‘lost’ directions (i.e. 8 Bevs)
Directional loops may be alternatives (e.g. K9AY, FO0AAA, TX3A etc..)

Malawi great circle map (tnx to NS6T) with VDA horizontal radiation pattern (click on image to enlarge)


One thought on “Antennas

  1. Very nice dxpedition and web site. I like the absence of ‘gung-ho’ machoism and the extremely sensible reliance on delta loop antennas – perhaps the best simple wire antenna possible.

    Good luck with the operation, and thanks for the rare 7Q QSO, despite a rather poor 12m band!

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