Wednesday 17 June 2009

Long wire and Un-Un part 1

I have been playing with a 4:1 unbalanced-unbalanced transformer and a long wire. The theory is that the Un-Un reduces the impedance at the feed point to a point that your internal ATU can cope with.

My first tests were with my 85ft end fed and were not too encouraging. These are the SWR results I got using an MFJ analyser:

1.9MHz >30
3.6MHz: 10
7.1MHz: 3.0
10.1Mhz: 5.7
14.150MHz: 2.4
18.1MHz: 2.9
21MHz: 2.6
24.93MHz: 2.0
28MHz: 5.7

from these you can see that the rig would be able to match the long wire on five bands. On test it would not match on 80m, although when run as a W3EDP through my external ATU it works well.

I then wound a 9:1 Un-Un (sometimes referred to as a magnetic long wire Balun) and tried again. Here are the results:

3.6MHz – SWR 28:1
7.10MHz - SWR 1.9:1
10.1MHz – SWR 3.6:1
14.2MHz – SWR 1.9:1
18.14MHz – SWR 3.8:1
21.2MHz – SWR 2.5:1
24.9MHz – SWR 3.5:1
28.5MHz – SWR 8.6:1

While 40, 20 and 15 metres were quite good I can't really recommend this as a multiband solution.

In all then, it is too long and not really worth playing with.

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