RadioBanter - View Single Post - From NEC2 to the real world with accuracy

Richard Clark · March 12th 08, 06:30 PM posted to rec.radio.amateur.antenna

On Wed, 12 Mar 2008 07:50:08 -0700 (PDT), wrote:

With respect to manually tuning the quad (reflector) after its up,
yes, that seems to be the conventional wisdom. How practical and
possible is that for me? Mine will sit on 72' US Tower crankup/tilt
over - short of renting some huge bucket/boom, I can't see myself
manually tuning it when its up. The best I will do is take some type
of field measurements and see if it displays anything close to the
pattern NEC2 predicts - or better yet, just see if I am happy with it
as is. I did not have to make any adjustments to the monoband yagi
that went right from NEC2 to the tower, so, I am hoping for the same
good fortune.

Hi Scott,

For tuning, one established technique is to get it up high enough off
the ground, pointed up, so that it is not affected by ground too much,
but still accessible by a ladder.

As for checking actual performance, note that in all practicality you
lack the means to measure the full 3 dimensional performance. Further,
even monitoring out 10 miles still puts you below the horizon, and for
HF that is barely more than a correlative, as nearly every NEC tool
shows performance above the horizon when it comes to the radiation
lobe characteristics. Otherwise you would need a helicopter....

You can measure against beacons, but now you toss in the variable of
propagation and you would have to marry the NEC output to WINCAP and
perform several dozen tests each day over the course of a month or
two. IF YOU ARE TALKING PRECISION AND ACCURACY.

On the other hand, you've already validated your testing, modeling,
and performance to your efforts for one band - Trust your tools and
data to be able to extrapolate it.

73's
Richard Clark, KB7QHC