[Elecraft] dBd vs dBi

Tue Oct 22 01:37:01 2002

On Mon, 21 Oct 2002 [email protected] wrote:
> elements for max gain and min SWR when you QSY, therefore bandwidth is
> not a concern like it is with other antenna manufacturers, so I don't
> want to sell the SteppIR short.
> 
> I don't know if their claim of 8.81 dBi gain is for every frequency on
> all bands from 14.000 to 29.900 MHz, but I can model 3-el Yagis for
> absolute max gain for say, 28.500 MHz, on a 16-foot boom to see if it's
> possible to achieve 8.81 dBi with a very narrow bandwidth.
> 
> Maybe one of you guys knows the frequencies for which their 8.81 dBi gain
> figure is valid for.  If so, please let me know.  Also, what kind of
> system do they use for matching to 50-ohm coax (when a Yagi is tuned for
> absolute max gain, the feed impedance is very low).
> 
> Will report my findings when I get some spare time to try it.
> 
> 73, de Earl, K6SE

Earl,

I asked the guys at FluidMotion for this information.  If they can give me
satisfactory answers, I'll probably go with their antenna.  It is just too
"neat" to pass up.

I've decided to put up a 72ft tower and just do it right the first time.

The 10-20m antenna will be either the SteppIR or the Force 12 that I have
been comparing.  (6m also if it's the SteppIR)

Also, I anticipate installing an M2 80M2LL2 (200lbs, 19sq ft) 2-element
80m yagi and an M2 40M2L (55lbs, 6.6sq ft) 2-element 40m yagi on the same
tower.  That will bring me to 285lbs of vertical weight, 29.6sq ft of
windload on the tower.  It has a capacity of 52.2sq ft at 70Mph so, I
think it should handle that just fine.  I'll be turning it with a
Prosistel PST61 (rated at 36sq ft and a vertical load of 2585lbs) rotator.

Since I'm in Columbus, OH, I don't exactly know how much fudge to leave
for ice loading, etc.  The tower will be pretty well protected from wind
by the surrounding (dense) trees and the house.  I'd say we'll probably be
exposed only 15-20ft over the treeline.  I'm not sure if that makes a
difference though.

My big question is with relation to proximity effect.  Do I have to worry
about how close to each other I mount these antennas?  I'm obviously
oversizing the tower so, I think I might be able to put a pretty long mast
on it to achieve some vertical seperation if necessary.

Anyway, this combined with the 540ft 160m loop should allow me to work
anyone I can hear with great authority using the K2.

73 de John - KC4KGU
K2/100 #2490
Elecraft WAS #8