With the two 8m tall masts erected on each side of our yard, it’s time to build the dipole!
Because I don’t like doing things by halves, I’m building a ‘multi-band fan dipole’. This is comprised of three dipoles, in a ‘fan’ layout. As explained here, I have so far built the centre insulator.
Center Insulator:
Now to run two lengths of copper wire up the sides (1.0mm mains cable should do nicely? 🙂 ), build an ugly-balun on the bottom, and measure out the cable lengths for the dipole.. The top run (40m band) will be 3mm stainless steel 7×7, as it’ll be carrying the weight. The lower two (or maybe three?! 😉 ) runs will be simple speaker wire.
Wire lengths should be:
| Band | Centre Freq | Wire Length | Notes |
|---|---|---|---|
| 40m (+15m) | 7.100Mhz + 21.3Mhz | 20.28m (4% short) | (I’m not interested in the upper 200khz of the band, as I don’t do CW) |
| 20m | 14.15Mhz | 10.61m | |
| 10m | 28.5Mhz | 5.263m | (note, using 28.5 rather than 29, as I am more interested in digital modes than anything else. And 2Mhz bandwidth is probably hoping for too much 😉 ) |
Note: this *was* originally calculated with a 30m dipole as well, but after modelling it, that was quite horrid.. (swr of 38 on 30m)
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