Topband: Make 80m vertical work on 160

[Franki ON5ZO]

Hello TopBanders!

In reply to my own posting a fortnight ago, I'd like to thank each and 
everyone offering advice and insights.
It seems that each of the options (loading coils, lineair loading and traps) 
to make a dual band vertical has its own fan club.

Given the fact that there seems to be no free lunch and in that respect that 
you can't have a cake and eat it too, I settled for a coaxial trap. Either 
solution has losses, but a trap does not need switching like a coil for dual 
band operation would. And no relay means no control cable, which in turn 
saves a small interface to switch the relay outside from within the shack.

That said I made a coaxial trap with thicker coax (H100) to cope with the 
QRO, and wrapped it tightly around a PVC form with 125mm diameter. I did not 
even get out my antenna analyzer. This option simply is too heavy to suspend 
on the L wire. I tried but the sag is too big and the support to keep the 
end of the L wire up in the air would suffer in the end.

There had been a little flame burning in the back of my head. So I unleashed 
the carburetor and injected some fuel into the antenna brain. There is 
another solution. A second antenna sharing the feed point and radial system. 
Worth a shot. Luckily I have a big pile of scrap bits and pieces and 
leftovers from previous projects. Here's what I came up with. I took some 
pieces of 16mm PVC electrical conduit about 30-40cm long. I drilled holes 
through those and used them as spreaders. That created two parallel wires 
sharing a common antenna feed point. They go up the telescopic tower (with 
pulley and rope) and up the tower they split ways. The 160m L goes to the 
left and the 80m L goes to the right. For testing purposes the tower is only 
2/3 up (15m). For contesting both tower sections will be cranked up (21m) so 
the 80m vertical will be full size and the 160m L wire will be approximately 
50/50 vertical/horizontal.

Sure enough the antenna analyzer showed two nice dip (160+80)s. In the shack 
I found that the MFJ auto tuner at the antenna's feedpoint accepted the 
impedances and took 900W on both bands. That's the good news. Now the better 
news: with some pruning I think I can get both bands to work WITHOUT the 
MFJ-998. That would be super. However I now have a working concept. A simple 
concept. No coils, no traps to burn, no relays to arc.

I had a ball last year on 160m with a totally random length system 'fooled' 
into 50 ohms by the autotuner. I worked into USA almost daily and worked a 
lot of new ones outside EU. I hope to do even better this year with the 
'nearly resonant' antenna. It may be far from the textbook figures for 
efficiency and take off angles but I think this is the best I can do given 
my location, budget and size of my garden.

Now if I could only squeeze in something for better RX. A K9AY loop fits but 
would be crammed and jammed between all the other antennas, which is not a 
good thing.

73 de Franki ON5ZO = OQ5M