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Richard Clark · June 21st 09, 01:08 AM posted to rec.radio.amateur.antenna

On Sat, 20 Jun 2009 16:13:07 -0400, wrote:

I switched to 527
because I can actually see a channel 23 transmitting antenna from my
window.

Hi Pat,

If you think this experience contradicts EZNEC (or conventional
teachings which it concurs with), then the confusion comes from the
sense of "very far away." Truly, if you can see the Channel 23
transmitting antenna, then it is not that far away in the scheme of
things. It merely points out that you have not correctly modeled your
experience.

For those who may not missed my original post, I find it hard
to believe a horizontal dipole tuned to the right frequency (near 1:1
SWR with 75 ohm source) would not be able to hear a signal coming from
zero degrees elevation. In the real world, there are all sorts of
reflections off of all sorts of things that will make it work, but is
it true that there should be no signal if everything was ideal?

What is going to be a reflector to a source that is bore-sight with
the horizon?

Richard explained the attenuation of the E-field. That makes sense to
me, but doesn't really explain the other nulls at 6 degrees elevation
and every 6 degrees above that.

You didn't ask about that.

There are strong positive lobes at 3
degrees and every 6 above that. The plot looks like a nice flower :-)
I would think that attentuation of the E-Field would explain zero
degrees, but as elevation increased, the attenuation would decrease.

You have, again, lost sight of the meaning of "very far away."

The EZNEC plot looks more like it is showing additive and subtractive
combining of the signal.

It is. What you see is called the Fresnel Zone if you were line of
sight.

Here, even if you can "see" the Channel 23 transmitting antenna, then
its various reflections could add up to ZERO. This, again, confounds
expectation, but it is the experience of every mobile operator who
encounters "picket fencing."

Another reply mentioned a different program
that calculated ground wave in addition to skywave. Maybe that is
what I am missing. I normally think of ground wave as why VLF, LF,
and MF signals travel further than line of sight, though. Does ground
wave have a significant effect at VHF/UHF?

Yes, it is dead within a mile for Channel 23.

I'm still confused,

and so are a number of your respondents.

73's
Richard Clark, KB7QHC

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