Hi Chris,
Thank you. Well, the impdeance has been resistive-capacitive, like a RC
series circuit, but mostly resistive. A few 100 Ohm on the feedpoint,
quite uncomplicate to match. I simply used a ferrite transformer with
about 300 turns on the secondary side and about 2x 20 turns primary, for
the PA that was running at 12V.
Now in spring it is certainly fun to play arround with long antennas. So
if you consider to use them for MF/LF/VLF RX or TX, do it! :-) Of course
you won't get 20% efficiency or so, even with a full size dipole. But it
is worth to play with. If you have a piece of forest arround, you could
build and run a small hidden transmitter and a small PA over night and
then take the stuff back in the next day...
Certainly worth a try.
73, Stefan
Am 05.04.2017 14:32, schrieb Chris Wilson:
Hello Stefan,
Wednesday, April 5, 2017
What impedance did you have to match with such an antenna used for TX
Stefan? Congratulations on your remarkable experiments at ULF, I am
stunned by what you are achieving "down there"!
Hi Jim,
Thanks for your comments. You bring me (back) to the idea of using
an earth antenna, this time for receiving.
In 2012 i build up a 700m long wire antenna in the forest. It was
grounded on both ends. I run a few 100 mA into the wire.
One day i put 250 W into the antenna and got 10 dB SNR in 3.8 mHz at 8970 Hz
in 45km distance.
I remember G3XBMs blog entry:
http://g3xbm-qrp.blogspot.de/2010/09/vlf-dx-transmission-with-earth.html
That was quite a nice time. Activity was much higher these days, not only on
VLF.
I also used the antenna for reception and was impressed by the interesting
frequency response.
In the next 970 Hz experiment i want to drive to
http://no.nonsense.ee/qth/map.html?qth=JN49JM36. During the
recording of the E field signals are running i have some time.
During this time i could try to use an earth antenna for ULF
reception. It has the advantage that it is easy to build it up in a
forest. Just 300m length or so. There has always been the discussion
if such an antenna (with grounded ends) acts rather as a loop or as
a dipole on the ground. I would expect a loop and so i will build it up.
Comments/Ideas?
73, Stefan
|
