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| To: | [email protected] |
|---|---|
| Subject: | Re LF: TIL Grabber restored... |
| From: | [email protected] |
| Date: | Tue, 19 Dec 2006 07:16:34 -0500 |
| Delivered-to: | [email protected] |
| In-reply-to: | <[email protected]> |
| References: | <[email protected]> <[email protected]> <[email protected]> |
| Reply-to: | [email protected] |
| Sender: | [email protected] |
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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 << [Keine Grafik]
[Keine Grafik]
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