9kHz Test, 2010-10-02

Amateur radio station DK7FC transmitting from 49.77647N 8.699525E (near Frankfurt), on 8970 Hz.


Three long periods of fairly continuous carrier were transmitted during this test, making it possible to analyse the signal in 700uHz bandwidth. Timing for the three periods was obtained by counting pixels on Stefan's Heidelberg spectrogram.


Todmorden Reception

Reception conditions were good, with no lightning in Europe and quite a low sferic background. Average background noise was some 50 to 60 degrees away from the bearing to Frankfurt.

Background noise and DK7FC signal amplitudes (+/-50%) are in the following table.

Transmission Noise bearing and amplitude DK7FC
1st2010-10-02_10:16:42,+141662.8 deg36 fT in 1Hz 6.1 fT
2nd2010-10-02_10:48:42,+194452.7 deg51 fT in 1Hz 6.8 fT
3rd2010-10-02_12:24:36,+181256.3 deg53 fT in 1Hz 9.2 fT

Best results were obtained with the loop antenna oriented towards DK7FC (rather than oriented to null the average background noise). Sferic blanking made a useful reduction in background. The signal was band-limited to 6-12kHz before applying blanking with threshold equal to the mean amplitude and no dwell time. Blanking was activated approximately 60% of the time and effectively removed all non-Gaussian noise components.

Transmission Without blanking With blanking
Noise in 700uHzS/N ratio Noise in 700uHzS/N ratio
1st2010-10-02_10:16:42,+14160.81 fT7.5 0.39 fT15.6
2nd2010-10-02_10:48:42,+19440.90 fT7.6 0.40 fT17
3rd2010-10-02_12:24:36,+18120.96 fT9.6 0.37 fT25

The effect of sferic blanking is seen in this spectrum of the 2nd transmission. The average background amplitude has been reduced to about half the unblanked level.

The 3rd transmission had a considerable frequency drift and it was necessary to apply a correcting de-chirp of 43.2mHz/hour in order to assemble all the signal energy into a single 700uHz bin. The effect of this drift compensation is seen below.

The S/N ratio in this test, after drift correction, was 25 (amplitude ratio), ie 28dB.