Multi-band dipole

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:

The 'center insulator' for my tri-band fan dipole

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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