Hi Wolf,
I thought about a resonated design which has a separate output winding
at 50 Ohm, fed to some meters of RG174 (to be far enough from the
netbook) and then to a preamp which i already have available (the M0BMU
design for the single turn loop). Then feed this to my homemade RX
which is way better than the 706 (in a comparison during the QSO with
HB9ASB there was nothing detectable on the 706+preamp while Anton was
perfectly audible on the homemade design (without the external preamp:
http://dl.dropbox.com/u/19882028/LF/HB9ASB.WAV)...
Am 15.08.2011 20:23, schrieb wolf_dl4yhf:
Hi Stefan,
For a resonant design (tuned with parallel capacitor) I'd use the litz
wire. For the broadband design (terminated with a low-Z amplifier) it
shouldn't matter too much, but 0.5 mm wire diameter would be the
minimum. The thinner the wire, the larger the 'R', R is noisy, and we
don't want noise ;-)
7 rods in a bundle, and two of these bundles sound good. But it depends
on the material (permeability) if it makes sense to use 8 "parallel"
rods - consider this: one single rod may already 'attract' enough
magnetic field lines from the far field; 7 rods will not attract 7
times as much ! Anyway for backpack operation you don't have the choice
to build a meter-long rod like Lubos' large antenna.
Yes, but 3 rods in series (= 0.42 m) would be fine as well. So i could
use 3x5 rods instead, or 3x3 if this would be sufficient.
Beware that my crossed-loop antenna was built for VLF, not LF.
I know. Thus using no litz wire is not so critical...
It was in 2003. Haven't known that your VLF observations started so
early ;-)
73, Stefan
Cheers,
Wolf .
Am 15.08.2011 19:26, schrieb Stefan Schäfer:
Hello Wolf,
Thanks to the link to your nice to read article. I just found it a hour
before your mail and already read it ;-)
Well, i also prefer the usual configuration instead of that sleeve
antenna. Also i have to keep the focus on my actual goal: Making a
handy antenna for amateur LF / p operation without a car! And the 16
rods i will get (14 cm long, 8mm diameter) will be best in a 2x7
config. i think. Or do you rather suggest 3x5 or even 4x4?
2x7 is then about 30 cm long which is very fine for a backpack and
should be robust enough.
I would use the same double side bonding tape, this is very useful to
get a first fixed arrangement. Then putting all that in a PVC tube, 2mm
thickness and add the turns above the tube.
Would you recommend litz wire or standard 0.5 mm enamelled wire?
As an E field shield i would use aluminium bonding tape, without making
a shutcut turn of course.
So the newcomers should not think that this antenna is the best what
one can use for LF. Just in that special case of /p i see advantages.
Otherwise a well designed loop (+ preamp or a very sensitive RX, if a
samll loop is used) or E field antenna such as the PA0RDT should be
preferred, as Alan already pointed out.
Looking forward to a direct comparison of the DCF39 SNR that can be
achieved and to the first amateur signal received with that antenna in
/p...
73, Stefan/DK7FC
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