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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