Content-Transfer-Encoding: 8bit
Message-ID: <3.0.6.32.20000309162256.008655f0@pop.saunalahti.fi>
Date: Thu, 09 Mar 2000 16:22:56 +0200
To: rsgb_lf_group@blacksheep.org
From: =?iso-8859-1?Q?V=E4in=F6_Lehtoranta?= <vaiski@dlc.fi>
Subject: Re: LF: Re: LF antennas
In-reply-to: <E12T1rl-0006VJ-00@mserv1b.u-net.net>
References: <3.0.1.16.20000309131959.21d7453a@mail.cc.kuleuven.ac.be><E12T0Ff-0005HW-00@mserv1b.u-net.net>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii; format=flowed
Precedence: bulk
Reply-To: rsgb_lf_group@blacksheep.org
Sender: <majordom@post.thorcom.com>

Hi all,  

Some time ago I wrote a story for SRAL magazine about (LF)
progation terminology with a drawing or a sketch showing
the proposed radiated components* near the radiating short
vertical monopole. Subsequently I asked comments from the
best "ground wave expert" I know, with much experience on
measuring ground waves both at ground level and in the air.
Especially how the radiated energy divides into components.
Refering to my sketch I gave examples of extreme cases of
short radiating element (10 m) and high one (645 m in Poland
until 1991). The measuring element was 1 m high with base
1 m above the ground level (the sketch is a 108kb TIF).
How to draw the inevitable "rays" fm one antenna to another.
Anyone having some good ideas or suggestions. de Vaino,OH2LX
Discussion abt what happens near the Tx antenna is needed...
- so far, no comments from my colleague mentioned... -

* the wave components shown as "rays" in the sketch:

- direct wave + ground reflected wave = space wave
- surface wave (at the interface: air/ground)
- ionospheric wave (separates into its own component) how?
- sub-surface wave (under the earth) its importance?
- GROUND WAVE which is the suggested term forpractical,
  measurable resultant wave (to some distance fm tx ant)

I read in "the LF Experimenter's Source Book" (page 1.10):

"All line-of-sight propagation will presumably
be by ground wave, as all aerials will effectively
be at ground level".

"Direct path (the Space wave), as used on other
frequencies will not work, as they involve both 
a direct wave and a ground-reflected wave".

"As the aerial height (in wavelengths) tends to
zero, they reach the same amplitude but opposite
phase and cancel out".

I have been sitting in an airplane at 100-200 m for
more than 500 hours while measuring LF and MF stations.
Does the above mean that, say 1-2 km from the transmitter
there is no space wave component (after cancellation)?
(not quite sure what is "line-of-sight" on LF frequencies)


----------------------------------------------------------
V.K.Lehtoranta, OH2LX, POBox 50, FIN-05401 Jokela, Finland
------ Tel: +358-9-4173965 ---- Fax: +358-9-4173961 ------
E-mail: vaiski@dlc.fi - alias: oh2lx@dlc.fi & oh2lx@sral.fi