Modelling the Butternut HF2V

I’ve been using a ground-mounted Butternut HF2V for several years now with great success – the basic model covers 40m and 80m bands. I was curious to see if I could build my own light-weight version of this antenna so modeled it to find the component values and also to see if the antenna could be lengthened (to improve efficiency) and still work OK.

I started by modeling the basic (80m, 40m) antenna; below are some results from MMANA assuming an antenna length of 10m and using four radials of 20m length. Using the values indicated in the picture on the left, I obtained (almost!) resonance on 80m and 40m (CW ends of band), as shown by the near zero values of Jx in the picture of the right. Note however that the radiation resistance is far from the desired 50 Ohms – that’s why the commercial Butternut product employs a simple matching coil at the base of the antenna (see picture of my installation at the bottom of the page).

I then lengthened the antenna to 12m and varied the coil values to see if I could again achieve resonance. I realised that by lengthening the antenna I would probably reduce the amount of inductance (coil length) in the design – the diagrams below show the results.

So my suspicions were confirmed – lengthening the antenna to 12m completely removes the need for the upper coil. Although I didn’t take this project any further, my intention is to eventually try this design out on a 12m long fibre-glass pole.

At my home QTH I have added the optional 30m kit to my HF2V, making it a tri-band antenna. I modeled this too, but came to the realisation that it is NOT possible to lengthen the antenna when the 30m option is in place. The results for the 10m long model are below. Note that Butternut supply a length of coax with the 30m kit that is inserted in-line to be used as a matching transformer (it does not effect the other bands).

The pictures below show the HF2V installed at my QTH. I’m fortunate to have good, conductive soil at my QTH and this helps immensely with the efficiency of the antenna. This antenna has worked over 250 countries on 80m in all 40 zones and has worked nearly 300 countries on both 40m and 30m.

There is an excellent web-page by DL7JV about home-brewing to the HF2V design here:

http://www.qsl.net/dl7jv/e.hf2v.htm