Markus,
Thanks for the description. I run the anti-thesis to you and live in
the basement with my operations and the up stairs is relatively noise
free. There are few power lines in the attic as there are only three
lamps in the house needing wiring via the attic. The attic seems like RF
'lebenraum' to me...
I should be able to work from your description and conjure something
up... I was null steering with the loop and large vertical and found
this instrumental in being able to hear DX by actively seeking and
destroying overwhelming noise sources even during QSO. The key being
able to wait for windows in the QRM.
Sometimes one sees a lot, through little.
73 and Thanks,
Scott
[email protected] wrote:
Hi Scott,
what I use here are two orthogonal loops (6 m^2 x 4 turns, see
http://freenet-homepage.de/df6nm/vlf/loops_small.jpg ), connected
symmetrically via ~16 m of twisted 4-wire cable with a common shield.
In the shack, there are tuning capacitors (~ 6nF) and transformers to
50 ohm outputs. I have also added a pair of decoupling capacitors
(~300pF, empirically found) between the primaries to compensate for
non-perfect orthogonal mounting.
The outputs are fed to a small goniometer, consisting of two pairs of
orthogonal coils. They are wound around the outside of 25 mm ferrite
ring cores, placed on top of each other
(see http://freenet-homepage.de/df6nm/Ferrite-Goniometer.gif and
http://freenet-homepage.de/df6nm/goniometer_small.jpg ). The cores are
simply used as a substitute for flat ferrite disks, and the windings
do not pass through the holes. 50 ohm match is achieved with
capacitors in parallel (~2 nF) and in series (22nF) to compensate main
and leakage inductance.
The goniometer is followed by a 3dB hybrid coupler, which can add an
E-field antenna component to achieve a steerable cardioid pattern. If
you have large and freestanding loops, you could double-use them as
E-field probes with a resistive termination - in effect a rotatable
K9AY ( http://freenet-homepage.de/df6nm/EH-Goniometer.gif ).
My low loops do not work very well SNR-wise, as they pick up a lot of
neighbourhood noises from underground wires and probably conducted
ground currents. The attic is not an option as this is where I (and
the noisy computers) live.
Hope this may be useful...
73 and good luck
Markus, DF6NM
>>
Thanks to those that responded direct with some advice.
However, my query was not about the wisdom of installing a crossed
loop in an attic but rather how to connect it electrically. I
understand the RFI issues as I live in one of the worst RFI spot
imaginable for LF operation. If one understands that there is no
better place to install the loops on my little lot, the attic looks
like a good place as it is at least out of the weather...
I need advice on electrical connection of crossed loops so I can steer
the null.
Regards,
Scott
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