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
The Patch antenna Cross polarisation problem - fixed.
Now the quadrature hybrid for circular polarisation.
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.