MIME-Version: 1.0
In-Reply-To: <Pine.LNX.4.64.1512201600200.28839@plato.ucs.mun.ca>
References: <Pine.LNX.4.64.1512191329320.26303@plato.ucs.mun.ca>
	<8D30934359654D8-15C4-3DDFF4@webmail-vm170.sysops.aol.com>
	<0EF07ED4EE1B45BDBB86B44B855B03BF@gnat>
	<Pine.LNX.4.64.1512201009490.28052@plato.ucs.mun.ca>
	<68629D3DB5E840F098999D75247C9777@gnat>
	<Pine.LNX.4.64.1512201600200.28839@plato.ucs.mun.ca>
Date: Mon, 21 Dec 2015 09:21:03 +1100
Message-ID: <CAKvcm2db1rbm0HFAcna7Q2HPW5qg57kafsVSKm4ep1dRc42-uw@mail.gmail.com>
From: Dimitrios Tsifakis <dtsifakis@gmail.com>
To: rsgb_lf_group@blacksheep.org
Subject: Re: LF: VLF in VO
Content-Type: text/plain; charset=UTF-8
Sender: owner-rsgb_lf_group@blacksheep.org
Precedence: bulk
Reply-To: rsgb_lf_group@blacksheep.org
Status: O

Hi Joe,

thanks for sharing your experiment details. I have been doing similar
tests on VLF, using about 120 m of wire, about 10 m of the ground. I
have used initially much less power, so signals disappear after a
kilometre or so. The attenuation over distance does seem to be a lot
more pronounced than you would expect and I think this has to do with
the fact that at a kilometre or so distance from the transmitter, we
are still in the near field of the antenna! This paper has some more
explanation and a graph of field strength versus distance (in lambda):

http://robotics.eecs.berkeley.edu/~pister/290Q/Papers/Antennas%20propagation%20interference/near%20field%20path%20loss.pdf

Anyway, how did you go about the 5:1 impedance transformation? I was
trying to radiate at about 10 kHz, so I used a beefy audio line
transformer (100V to 4 ohm/8ohm), but I am not sure how efficient this
is.

73, Dimitris VK2COW/VK1SV


2015-12-21 6:46 GMT+11:00  <jcraig@mun.ca>:
> It was a nice but windy day today so the VLF TX was put on the air
> for a quick test.  About 30 watts were fed to a 5:1 XFMR and a ~0.35H
> tuning coil to the 100m wire at 10m height.  CW signals were heard
> clearly at 2 km using a homebuilt DC RX and a PA0RDT miniwhip at 2 km.
> The sigs could not be heard on the DC RX at 2.7 km and were much weaker
> on the XH100/LF10 with 20m of wire strewn in the trees.  This is
> a new distance record for me for audible reception at 8.277 kHz. The
> ERP was about 3uW.
>
> 73
> Joe VO1NA
>
>