Low Band Antenna Development: 80m confirmed

A lot of work has been going on in the background building the antenna system that I will take to Vanuatu this year. That work culminated in a first successful on air test this weekend on 80 and 40m. This is a positive development and confirms that 80m will be one of the active bands from Vanuatu next month! I huge thank you must go to Steve VK5SFA who has helped with the design and field validation work and also to Paul VK5SL for his insights as well.

Antenna Design

The antenna is based on the 40m folded monopole solution that was used last year on Niue, but scaled up to 80m. Mechanically it is now based on a 12m Spiderbeam. The design allows for the main radial to be variable in length as well as the ground radials, such that the whole antenna is effectively tune-able from 80m-10m). The design has been modeled in 4NEC2. The results are shown below for 80m.

Structural Details

The design is based on the following basic components:

  • 2x Fly Fishing Reels
  • 1x Nylon cutting board
  • 1x 3 terminal screw block
  • 8AWG enamel copper wire
  • 1.5mm dia 7×19 stainless steel wire (for the driven element)
  • 1x 12m SpiderBeam pole
  • 2 sections of a 9m Squid Fishing Pole

You can see the construction method here:

Field Test

Out in the field the mast was rigged such that the guys provided the spacing over the top of the mast giving it a peak height of 12m. Groundwave QSOs on 80m were achieved over ~20km at 59+30dB for 50W in daylight. The coil in the first run had too many turns so some more fettling is required there. We also achieved some late afternoon 40m contacts with the coil out of circuit and the driven element wound in resulting in a native 1/4 wave that matched 50ohms. No reason to think it wont tune 30m as well as 20-10m. Next steps are now to tidy up some of the mechanics and then retest with taping the coil in various places.

Once 80-10m are working, 160m will be tried with a top hat loading wire and a counterpoise radial. 160m is still an experiment and is not guaranteed. However we may be lucky.

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