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.
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)