Thomas
Braunstorfinger und Martin Hisch, GbR
|
|
|
|
To decode morse signals (often called "CW signals") Analyzer2000 must be connected to the audio output of a HF receiver. In normal operation mode a human listener would decrease the bandwidth to the minimum value the receiver is capable of. This eliminates all unnecessary signals. Only the wanted signal passes the receivers bandfilter. Analyzer2000 leads to another way of morse decoding. In a HF scenario, especially in middle europe, many CW stations can be detected in a small frequency range (e.g. 3 kHz). The idea is to decode all morse signals in this range simultaneously. To do that, the receiver bandfilter must be reasonable wide, for example the SSB filter which should be 2.4 to 3.1 kHz. The arising gain control problem can be eliminated by switching the receiver to MGC (manual gain control). Each Analyzer2000 morse decoding window has its own gain control (either manual or automatic), by adjusting the threshold limit. A normal scenario may look like
this:
Decoding of morse signals is a job quite simple for a trained human brain. Decoding with a machine is almost as simple, if you help the machine in some aspects. First of all the update rate of the spectrum display should be greater than 30 frames/sec. For high speed morse decoding (speeds greater than 130 letters per minute) the update rate should be greater than 50 frames/sec. With the FFT control dialog box the update rate can be varied. On slow PCs the waterfall display should be freezed while decoding morse signals. Also the time domain window should be closed. If two signals lying close to each other, must be separated, the width of the rectangle must be decreased, simulating a smaller bandpass filter. If the signals interfere each other, FFT size, points and overlapping must be increased. That makes the signall peaks in the spectrum display sharper. A kind of noise reduction can be established by decreasing the spectrum displays level range coupled with varying the reference level. The second thing is to adjust the speed of the morse decoder. There are two automatic modes of operation (fast and slow). Fast mode tracks the speed of the morsing station very quickly. The disadvantage comes up, when the scenario is very bad (QSB, QRM, QRN). The interferences irritate the speed tracker and only rubbish is being printed. In that case, the slow tracker is better, but the best thing is to let the fast tracker measure the speed in a moment of good signal condition and to switch to the third speed mode called "fixed". In that mode the measured speed is held and can be manually varied with the arrow controls beside the speed display. The advantage of the slow speed tracker comes up, when a signal is constantly monitored over hours via the logfile option. In that case the morse speed is adjusted continuously to the correct value without any user interaction. A morse decoder window may look
like this:
|
|
Please direct questions or comments regarding this website to
webmaster@brownbear.de
|
