[iblackford]

I've been doing some reading on different antennas, and came across a "ZL Special" antenna model that seems to be popular for HAM's.

From what I have read, for a given boom length you can realize higher forward gain with the ZL special compared to a yagi.

Has anyone modelled a ZL special for OTA use? If not, what are the reasons not to?

 

[holl_ands]

I have not modeled the "ZL Special", but it's obviously a Log-Yagi with 2-Element LPDA driven pair and
a bunch of passive directors (and NO reflectors????). A Log-Yagi CAN be better than the sum of its parts:
http://www.hamuniverse.com/gi6jpozl-special.pdf
If you were to simply rescale it to Hi-VHF or UHF bands, it probably would cover only a few channels.....

W-G YA-1713 is a Log-Yagi with 2-Element LPDA driven pair, a reflector and 7 directors.
RCA ANT-751 is a Log-Yagi with 2-Element LPDA driven pair for Hi-VHF, NO reflector and 2 directors.
Although Raw Gain is believable, I ran into difficulties trying to calculate SWR for both using 4nec2.....

Cebik has some articles re "Log-Cell Yagis" here:
http://www.cebik.com/content/radio.html
FREE Registation required to access....

There is a DOS based design program LOGYAGI.EXE you might want to take a took at,
but be sure to run any downloaded software through a virus check program....
BTW: I found LOGYAGI.ZIP which contained a RUSSIAN spread sheet....but it was LPDA, not LogYagi.

The difficulty with DIY designs, whether standard Yagi or Log-Yagi, is determining the
OPTIMUM design parameters....the big boys use optimization routines to "find" a solution
that provides good Gain and F/B Ratio across the entire band....not an easy accomplishment.....

 

[Dalek Prime]

RCA ANT-751 is a Log-Yagi with 2-Element LPDA driven pair for Hi-VHF, NO reflector and 2 directors. Although Raw Gain is believable, I ran into difficulties trying to calculate SWR for both using 4nec2.....

It looks like a crossbow, and probably works best as one. I think psi would be simpler to calculate for it.