RadioBanter - View Single Post

January 30th 05, 05:02 PM

On 29 Jan 2005 21:57:40 -0800, wrote:

A 150 foot boom ( say 20
elements for example) beam might be perfect for picking up t he lower
angle, which is what I thought you were looking for. The t hree
element beam will bring in higher angle signals as the lobe will
have
a higher angle. A dipole will likely have even a higher, po ssibly a
NVIS angle. ...................................

Dunno...I've never compared super long yagi's vs short ones, but I
don't
think boom length has a drastic effect on the takeoff angle...The
height above
ground is what really determines that...Same for a dipole...A dipole
has a very
low takeoff angle *if* it's high enough..The various yagi's takeoff
angles *should*
be about the same as a dipole at that same height...Or seems to me,
without
looking into it farther. MK

I believe that the TAO is narrower, but, like you said, it is really
affected by height and terrain. The range of the TAO of a short beam
might be -25 to +25 and a long beam might be -10 to +10 degrees
relative to horizontal (assuming maximum height of the antenna).

We are in agreement here. The author wants a small footprint antenna
to have a very low TAO, but I think that elevation has more to say
than does the antenna design. A three element beam at 20 feet might
have a TAO of 14 degrees, but the only thing you can do is point the
antenna in the direction you want. I can see pointing the antenna
upwards to get a more vertical TAO, but pointing it down won't give
you a lower one. Like you say, it takes elevation for that and then
it depends on the frequency. If that elevation is 125 feet for 20
meters how can an antenna change it to a lower elevation?

Thanks for the input. I think I have been confused as to what the OP
wanted for an answer and no doubt my answers are confusing too.
Strangely enough, I am thinking that except for the desire of the OP
for a solution, everyone in here is in agreement with the technology.

73

--
Buck
N4PGW