Message-ID: <4E64BEB6.7000002@iup.uni-heidelberg.de>
Date: Mon, 05 Sep 2011 14:21:10 +0200
From: =?ISO-8859-15?Q?Stefan_Sch=E4fer?= <schaefer@iup.uni-heidelberg.de>
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To: rsgb_lf_group@blacksheep.org
Subject: LF: Loop vs. ferrite antenna tests...
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LF,

There was no chance for me to TX in France this year but at least i did 
some useful comparisons with my single turn loop (1m diameter) and the 
ferrite antenna.

Markus/DF6NM did some CW beacon transmissions on 136.5 kHz for me. The 
distance was 428 km 
(http://no.nonsense.ee/qthmap/?qth=JN59NK&from=jn29od96).
Both antennas were pointing to DF6NM. The whole system was running on 
batteries and the distance between antennas and netbook was sufficient. 
Anyway there was a noise pickup, maybe by the local 20 kV line in some 
10m distance.

Best S/N for the loop was achieved by using the preamp + a 10 dB 
attenuator. Without the attenuator, the RX gets overloaded due to DCF39 
which is still very strong there. Without the preamp, the noise floor is 
to close to the soundcard+RX noise it seemed. It was a relatively quiet 
morning, just some individual cracks / QRN.

The ferrite antenna was used in combination with the same preamp (M0BMU 
design, 50 Ohm based), but without the attenuator.

The audible performance of the ferrite antenna seems to be even slightly 
better than with the loop. This is due to the smaller bandwidth (higher 
Q) of the ferrite antenna that reduces the DCF and HGA levels even more. 
Markus was well audible on both antennas! The S/N was about 20...23 dB 
in 3 Hz noise bandwidth.

A comparative spectrogram can be found at 
http://dl.dropbox.com/u/19882028/LF/DF6NM%20in%20CW%20in%20JN29OD96.png
First one can see the ferrite antenna (slightly lower signal level but 
about same S/N) recording, then the loop.
SpecLab was using a 10th order butterworth filter centered to 137 kHz, 
with 2 kHz bandwidth. The noiseblanker was applied as well (9 dB treshold).
An audio file can be found here: 
http://dl.dropbox.com/u/19882028/LF/DF6NM%20in%20CW%20in%20JN29OD96.WAV
It uses a 500 Hz CW filter at 700 Hz AF. Except the filter and blanker, 
no further noise reduction is applied.
I personally find the first part of the file better to copy. This is the 
ferrite antenna!

Tnx Markus/DF6NM for the test.

73, Stefan/DK7FC

PS:
Copied further stations:
DG3MDE : http://dl.dropbox.com/u/19882028/LF/DG3MDE.jpg
DF6NM at 35 dB S/N in 488 mHz: 
http://dl.dropbox.com/u/19882028/LF/DF6NM_QRSS-3.jpg (wrong locator in 
the capture)