Hi Rik and Johan I triggered Laurie to run his models for EZNEC again ( I am
like that ....get other people to do my "dirty work" ...hehe ...thanks
Laurie) again with a commercial vertical 1/4 wave at 500k and and amateur
10m inv "L". Now , yes I know EZNEC does not simulate ground conditions
well, but it was instructive to see that there was little difference in the
zero-angle radiation for the quarterwave vertical. but the 10m "L" put
considerable more up in the air ~5deg over poor ground. Even the 10m "L" put
out good zero angle radiation over perfect ground.
Cheers de Alan G3NYK
----- Original Message -----
From: Johan H. Bodin <[email protected]>
To: <[email protected]>
Sent: 19 June 2007 00:36
Subject: Re: LF: M0BMU ERP on 500k
Rik Strobbe wrote:
> Looking at the patterns:
> am I right to conclude that not-so-perfect ground will only attenuate
> the surface wave (radiated at 0�) but will not affect skywave (or even
> improve it a bit)?
I don't know... But, experience from experiments, software simulations and
reading a lot of books converge into the fact that vertical antennas over
non-perfect ground do not radiate well at zero elevation. I believe it
has something to do with the GND beeing a not-so-perfect mirror which,
in addition to beeing lossy, also has some phase shift in its reflection
coefficient. I guess...
I think that most of this attenuation happens in the near field region
which I believe is exactly what Jim M0BMU has found in his experiments;
the FS falls off almost linearly with distance but it is a few dBs
"too low". An FSM antenna at 2m height is below 1 degree elevation
already at 114m distance from the TX (assuming that the Earth is flat,
isn't it? ;-) )
73
Johan SM6LKM
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