Inverted-L

INVERTED L 80/160m

I wanted to discover the lower bands like 80 and 160m so I built this inverted-L. There was two differents version, the first with a vertical part of 8m, then the second to 17m. On 80m, the first L was correct but very bad on 160m, with this upgrade I can now make more QSO on the top band.

My power is limited to 100w from the Kenwood TS480, so if you have good ears, maybe you could hear me on top band.

When I was looking for an inverted-L I found this website :

FO8RZ : Phil describes his inverted-L for 80 and 160m.

INTRODUCTION

My definitive antenna is looking like this :

- Vertical part of 17m then a wire of 13m at 45°

- 8 radials of 20m and 4 radials between 10 and 4m

- 160m : Coil about 25 µH on 10cm form for 160m

- 80m : 3 Coax capacitors about 50 pF each in parallel. Total 150 pF before I cut them step by step for adjust the SWR on 80m.

- Choke balun on a toroid FT140-43 : about 12 turns of enameled copper.

- The toroidal transformer ratio can be inversed 1:1.6 or 1.6:1

- 80 or 160m are chosen with relays

I designed the transformer at the first antenna version (with a vertical part of 8m). In this configuration the impedance without the toroidal transformer was :

- On 160m with the 25 µH coil : 90 ohms

- On 80m with 3 coax capacitors : 34 ohms

So I decided to take a ratio of 1.6 and reverse the transformer according to the frequency band. I don’t know if this design respect the theorie, but it seems to work well. During the first version the SWR was about 1.1. In the second version , impedance have been modified by the change of vertical part lenght, so the SWR increases a little bit. For the moment I prefer to don't modify anything on the UnUn.

TECHNICAL INFOS

This antenna allow me to be QRV on lower band, it was the main objective and it work fine. Of course, its possible to improve the system in adding more radials or replace the transformer. It will be maybe my next technical trip...

If you want to give an advice on the transformer, you could contact me by mail (see on «QSL & News» page).

CONCLUSION