On 9/10/2012 9:01 PM, Ralph Mowery wrote:
wrote in message
...

If they rated a ringo using dbd, it would be zero.. Which doesn't
look too good in the ad's.. :|
So they use dbi to make for manlier gain figures..


I think CC just pulled numbers out of the air. Especially in the eairly
days. Just looking at an old ad from 1974. They rate the 2 meter Ringo at
3.75 db gain. No refferance as to what.

Also the 11 element was rated at
13.2 db of gain.

Which was quite a bit shorter than the CC 214WB. The 214WB, which was
better when you took off the marketing based "trigonal" reflector, still
only made 11.91 dBd on a 14' 11" boom when optimized (based on your
preferences).

BTW the maximum reasonably obtainable gain on a yagi with a boom greater
than 1 wavelngth is predictable with the following equation -

G = 10 log (5.4075 B + 4.25) for B GT 1

Where G is gain in dBd and B is boomlength in wavelengths.

I worked this out in the early 90's from a database of over 100 of the
best practical, buildable VHF/UHF yagi designs. Thanks especially to
K1FO for all of his design work. His 432 yagis had the greatest effect
on the numbers. W1JR thinks it's accurate, so who am I to argue?

I designed an extended version of the 214 that lets you re-use the
useless extra reflectors as directors. This had a 17' 7" boom and would
make 12.43 dBd at 144.2 with a decent feedpoint impedance of 21 ohms and
F/B of 24 dB. This was used successfully at a friend's place for a 2 by
2 EME array. The antenna was tested at Central States and met the
computer predicted gain exactly.

If you want crazy I have a 432 EME antenna that does 18.4 dBd (according
to the model) which tested at 18.1 on the range. They said the range
was too short to test the antenna. It was still the highest gain for a
homebrew 432 ever tested at Central States.

Anyone that wants any 6m to 70cm designs can drop me an email. I've got
lots.

tom
K0TAR