Date: Wed, 28 Apr 2010 23:11:50 +0200 (CEST)
From: Jacek Lipkowski <sq5bpf@lipkowski.org>
To: rsgb_lf_group@blacksheep.org
In-Reply-To: <4BD86B78.8000602@gmx.com>
Message-ID: <Pine.LNX.4.64.1004282254370.21716@paranoid.lipkowski.org>
References: <003201cae3db$b7ffad50$0301a8c0@your91hoehfy9g>,
 <006e01cae6e3$2d46f4b0$4001a8c0@lark>,
 <BF4A524700075746A6467658DFC7102C19A2156E84@ICTS-S-EXC2-CA.luna.kuleuven.be>
 <4BD85BAD.18368.2436C56@dave.davesergeant.com> <4BD86B78.8000602@gmx.com>
MIME-Version: 1.0
Subject: Re: LF: Re: W1VLF 8.97 KHz UPDATE  Trees,  Questions, Ground
Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed
Sender: owner-rsgb_lf_group@blacksheep.org
Precedence: bulk
Reply-To: rsgb_lf_group@blacksheep.org


On Wed, 28 Apr 2010, Mike.WE0H wrote:

> Most people thought a TX loop would not radiate out of a backyard.

a few years ago i've tested some very modest setups (no kilowatts and 
kilometers of wire).

in a country area 1 km is certainly possible with a 4x14m loop made of 
pieces of 4mm2 and 1.5mm2 wire (if i remember correctly). the power was 
abt 40W and the matching was done via a capacitive divider.

btw. 1km is more than my backyard :)

you can also get 500m easily with a 1.5x2.5m 3-turn loop in a city area.

> The calculations say a TX loop is a terrible antenna, but it does 
> radiate very well.

yes and no. the calculations are correct in free space, however it has a 
very strong near-field, which will couple into anything that will conduct 
(powerlines, underground streams etc). thus if you're not in the cosmos, 
then in a realistic setting the antenna size is much greater.

actually someone on this list called it "cheating" :) it's interesting 
that this cheating by law of recipriocity should increase the receive 
antenna size too.

as mentioned above, with a very small loop i can do 500m in the city. this 
is probably because of all of the underground conductors here (powerlines, 
phone lines, catv etc).

VY 73

Jacek / SQ5BPF