6m ZL Special, is the ZL really special?
6m ZL Special on my mini tower, top, Dual La-Porte rhombic
6m ZL Special, SWR plot 1MHz/cm (return loss)
GI6JPO ZL Special, note folded dipole feed, from the 1970s
Note also all the dis-similar metal problems.
Understanding the Hex Beam by G3TXQ
2m antenna trials
6m Auzzie Station Master, ruggedised for repeater
23cm. Read from page 128, Short Backfire Antenna (SBA or SBFA)
3GHz, Short Backfire Antenna, a 1971 DOD article, note crossed dipole feed page 5.
From article NQ56152.pdf, circular cup shaped reflector, a bit bigger, 2.6Y is better.
Page 528 or 509 in the doc, Short Backfire Antenna, crossed dipole feed 14db gain.
Similar gain to their 16el yagi. Front to back is a bit poor, only 2.05Y dia.
Perhaps, 2.6Y (above) is better.
Great "ZL Special" thoughts on page 511 (p492) Multi-Feed yagi, Quad page 514.
Why didn't they add the Multi-Feed to the 16el?
Greek Microwave Group, SBFA
Section: Practical Cavity Antennae
Note the SFBA can have greater than 100% aperture efficiancy!!
Thus far no info on MATCHING. The dipole feed implies 50 ohms.
Well I built one for 70cm and the feed impedance is well below 50 ohms.
and quite narrow band, 1%.
Also I'm interested in both LH and RH circular polarisation simultaniously.
Simple because of the single dipole feed and the antenna's symmetry.
For circular pol. a hybrid will be near the feed.
70cm SBFA, improved and, more improved.
Once I understood "sleeved", (read Antenna-design.pdf) I get what the extra disks are doing.
I added a disk as per "Improved" and my VSWR bandwidth is now a good 20MHz. Now I can use it!! Well not
quite, what's it's pattern?
Circular Polarisation is easy now, but few EMEers use Circular on 70cm.
I note now, the back-screen shape of the SBFA is not arbitrary, so an antenna-range
where one can adjust everything is a must. NO-GO for a DIYer like me.
Next, a phased array on a 1.5m x 1.2m fly-screen sheet.