Message-ID: <E9CC57E686C74B69937AB6DD0B1B4580@DuoLaptop>
From: "PY2PLL" <py2pll@py.qsl.br>
To: "RSGB LF Group" <rsgb_lf_group@blacksheep.org>
References: <49A91070.9040902@freenet.de>
In-Reply-To: <49A91070.9040902@freenet.de>
Date: Sat, 28 Feb 2009 22:04:48 -0300
MIME-Version: 1.0
Subject: LF: Re: "Silence of the Lamps", etc
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Hi ...

>
> On the same website, there is also an article about a varctor tuned loop
> antenna, where the author found the "Q" of the resonant antenna was
> higher when tuned with varactor diodes, than with an air variable
> capacitor (?!) :
>
> http://brneurosci.org/loopantenna.html
>

NTE618s are rare down here but I have some for testing. Actually I'm 
building a regular MW loop for external mount (rotor oriented, remotely 
tunned, 12AT7 tube as a balanced buffer, etc) and I'm using this event to 
test some parts: the 12AT7 cathode folower versus a 2xJ310 one, tunning 
element (NTE6128 X air variable X cheap film insulated MW radio variables).

I don't want to use the traditional pick up loop ... a 10 turn antena X 1 
turn coupling loop will present to receiver a Z between 100K <> 1Mohm! On my 
configuration, I'm picking up RF signals using those Hi-Z buffers right from 
the coil ends, e.g the places where tunnig elements are connected.

And I'm doing some real measurements using local AM pests using a W&G SPM33 
SLM. The first results shows that when NTE618 is used the received signals 
drops 12dB average when compared to an air variable capacitor. As expected. 
Ok, there's a lot of signal anyway, with 618 or air variable, it's simpler 
to use varicaps to remote tunning but ... I want the 12AT7 + air variable 
there :-)

Diagrams + photos (texts in portuguese for a while, sorry)

Theory + table comparing components expected thermal noise: 
http://py.qsl.br/loop_om.htm
Tube Buffer = http://py.qsl.br/om_buffer.htm
J310 buffer = http://py.qsl.br/a_pratica.htm

73
Marcus Ramos
PY3CRX/PY2PLL
São Bernardo do Campo - SP
http://py.qsl.br

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