40m OCF Dipole

[ Version 2-2 ]

Dual-Core 4:1 Guanella Balun


An IMPROVED Version of Ver. 2

of my Ultra-Light 40m OCFD.


This version replaces the single core balun of Ver. 2 with a dual core balun.  This improves the balance by forcing equal currents into each side of the antenna (which a single-core 4:1 Guanella does NOT do.)


NOTE:  The feedpoint was moved slightly closer to the end:  40.3%


All other physical characteristics of this antenna are identical to Ver. 2, including 12m (40 ft.) of RG-174 coax.


The SWR curves are basically identical for both versions.


If you look VERY CAREFULLY, you can just spot the green polycarbonate spacer between the two cores.  This tiny "doughnut" is 2mm thick, and prevents the windings from the two transformers from interacting.


I'll upload SWR curves later, but if you must know now, just view the curves on Ver. 2 .

(They're close enough for government work.)


The Completed Antenna:


This ended up weighing about 17 gr. more than the single core version.  (peanuts)

Total Weight w. Coax: 348gr. (3/4 lbs.)


Although the smaller cores won't handle as much power as the single larger core, it is still more than adequate for the power level intended for this antenna (100w).


I tested the balun on 40 and 10m at 300w for 5 minutes on a 4:1 mismatched load. Results: no warming on 40m but on 10m the two cores became a little warm, though not really hot. By that time the dummy load was too hot to touch.


The antenna pictured here is the first prototype.





If you compare the SWR curves, versions 3, 4,  and 5 all have better SWR curves, especially on 40 and 20m.  



COMMON MODE CURRENT (The Beast that Bit my Coax) is almost non existant on this version (with this power level), whereas it is significantly stronger on the higher versions of my 40m OCFD's.


Though the SWR curves of this version are not quite as good as that of Ver. 4, this version is better on 17 and 12m.  It requires a matchbox on these two bands but is still low enough as to produce excellent results on these two WARC bands.


For most installations, I believe a more symmetrical antenna will be preferred (i.e. the closer to the middle, of the antenna we place the balun, the better).  If it happens that someone prefers a solution with the feedpoint closer to one end, they can choose ver. 4.



Moving Forward


I liked this version so much that I created a name and model for it.

It is my Aerial-51 Model 404-UL




Model 404-UL


  • Ultra Lightweight


  • Only 400 Grams (14 Ounces)


  • 7 Usable Bands


  • For many transceiver, most bands are usable without a matchbox.


My Favorite!

More Info: