Vertical Off-Center Fed Dipole for 6m

An older post on VOCFDs at KB6NU's blog scampered across my field of view this week, so I had to adapt it for 6 meters.  Six meters is a really cool band: low VHF, can sometimes duct as expected of VHF, can sometimes skip like HF, is on pretty much everyone's HF transceiver, and completely is under-used.  Mostly though I'm interested in it for its local VHF properties: line-of-sight, with some ability to crawl around hills and penetrate piney woods.  Throw in that shiny new 9:1 unun (link, scroll to the bottom) and I'd have everything already in house, all ready to go.

Now a note about that antenna design post... it's largely correct, but some of the math is a shade off.  The ultimate result, X1 = 0.131 * X is correct, but if you want to work it yourself, remember that the feed Z is 450 ohms, not 50.  Also, be sure to do the arcsine calculation in radians, not degrees.  But as I said, the ultimate result for X1 is correct, and of course X2 = X - X1 (referring to the sketch at the above-linked post; but X, X1, & X2 are respectively total length, short end length, long end length), so everything's easy.

I wanted things tuned for the center of the 6m band, namely 52 Hz.  Cranking the formulae and tacking on 3% more for insulated wire gave X1 = 1.2157', and X2 = 8.0643'.  Cut some #20 wire, assemble, hang, measure resonant frequency... and get 39.2 MHz.  Hm, that's pretty far off the 52 MHz target.

A half-hour of cut-and-try and I wrestled it down to SWR = 1.5 across the 6m band, for X1 = 1.04' and X2 = 6.46'.  That's weirdly short, but it does seem to work.  Then I recalled about that LDG unun: it's only rated to 30 MHz.  But what's an extra 20 MHz between friends?  Good enough, hook up the FT-817nd and take it for a spin.  Like I said, it seems to work, with low SWR and some unknown digital somethings received.  Didn't make any contacts, but then I wasn't really expecting to under the current conditions.

Testing will continue.  In the meantime though, it was a nice afternoon to spend playing radio on the back lawn.  Here, have some pictures:

  

L: the slightly suspect unun.  R: FT-817nd in its native environment.
As always, click to embiggen.  These pics really do benefit from increased size.

ps: Looking back on this post from Tuesday's perspective, I really needed a slow goof-off Saturday last weekend, and that's what we got here.  Need another.