Richard Fry wrote:
On Nov 29, 1:10 pm, Roy Lewallen wrote:

As you can see, you can get reasonably good results using
EZNEC+ and near field analysis, although the vast majority
of people this intensely interested in the mechanisms of AM
broadcasting aren't hobbyists but rather professional
engineers who are using EZNEC Pro/4.
________

Thanks very much for your numbers and comments, Roy.

I would never have thought to try to use EZNEC near-field analysis to
compute the groundwave if I hadn't read the suggestion to do so in
this thread. That was my first, and will be my last attempt at that.

I've suggested it to you on at least one of the several occasions you've
brought this subject up, in the thread "Rhombics" on Oct. 1, 2006.
I've also mentioned it at least 10 other times on this newsgroup going
back as far as 1998. Reg used to entertain himself by periodically
complaining about EZNEC's lack of ground wave analysis, and most of
those postings mentioning the near field technique were in response to
his postings. I see you've taken on that aspect of Reg's former source
of entertainment. You and Reg were just about the only hobbyists who
have this intense interest in EZNEC and ground wave analysis, and now
that Reg is gone it's pretty much down to you. Of course you could
directly get the results you want from NEC-2, which is free and readily
available. I assume the reason you don't simply do that is that it
wouldn't be as amusing.

When I need to calculate the MW ground wave for a particular distance,
monopole height, frequency and ground conductivity I use the FCC
method of first determining the inverse distance field of the radiator
at 1 km for 1 kW of radiated power, and then using that value in a
program I have with the FCC's MW propagation curves in digitized form.

Since you can use this method to get results you believe to be correct,
why do you need EZNEC? If you want another program to give you the same
answers, why not use NEC-2? NEC uses the same method as the one used to
generate the FCC's curves. But I believe the FCC curves account for
Earth curvature while NEC doesn't, so I'm told they begin deviating at
somewhere around a couple of hundred miles.

My point when starting this thread was to show that the elevation
pattern radiation actually launched by vertical monopoles on any
frequency does not have a zero/very low relative amplitude at/near the
horizontal plane, which from what I read on these NGs seems to be a
popular belief.

I don't believe I've ever read that. But if anyone does believe it, a
much larger number believe just about the opposite -- that the signal
strength from a vertical is maximum at zero elevation angle at great
distances from the antenna. This of course comes from the ubiquitous
plots of the pattern of a vertical over perfect ground.

Guess that's enough for now. Maybe you can go a little longer before
bringing it up again the next time? In the meantime, I suggest you
either update your v. 4.0 EZNEC demo program or replace it with v. 5.0.
The demo programs are still free.

Roy Lewallen, W7EL