RadioBanter - View Single Post - Impossible-to-build Yagi

September 12th 03, 05:21 AM

(Peter) wrote in message om...
Ok so there are lots of different designs that supposedly have
different strong points. Suppose I just want to go for maximum dB. How
do I achieve that? Does anyone have a site that explains what
parameters to use to achieve that?

You would want to build an "NBS" yagi if you want max gain and so-so
f/b.
There are many examples of these in the ARRL antenna handbook. They
have examples and specs for all vhf/uhf bands, also for differing
numbers of elements. All those examples for 432 use 3/16 inch element
dia. Element diameter is very critical to building a UHF beam. So that
means trying to design one on the puter is a waste of time, unless you
start out using the exact dia tubing you plan to use. This makes
scaling antennas from other bands with fatter tubing a pain. You will
likely end up with an oddball element dia if you scale a normal dia.
So its best to hunt down a good plan, and stick to it. Exactly.

And can anyone explain this. When I ran the DL6WU Antenna Design
Program and fed in my parameters (433.92MHz, 5mm thick elements,
plastic boom) it gave me a set of lengths and spacings and a supposed
dB of 12.1. But it had the DE and D1 3.4mm apart from centre to centre
meaning that with 5mm rod they were actually touching! I separated
them a bit and fed those lengths into Yagi Analysis 3.4 and it gave me
a dB of 4.9.

Dunno... Like I told Art Unwin a while back, I don't have much use for
antenna design programs and "optimizers" etc...Seems to me the vast
majority of the output is junk. I always get better results if I do it
all manually, and let common sense rule. But for UHF, I'd just find a
plan and use it. The examples in the ARRL antenna handbook are exactly
what you want. I don't know of any sources on the web. You can use
eznec demo and scale the "NBS yagi" it has, but then again you are
back to worrying about the element diameter scaling and whether any
real tubing will match what it spits out. The example is for 6m, and
using 1/2 inch tubing. No telling what that would scale to for 432
mhz. MK