I spent part of my engineering career designing satellite command FSK
demodulators - including the deep space Pioneer Venus orbiter. To test
the performance of them, we would mix the test signal with white noise.
When you look at the FSK Bit-Error-Rate (BER) curve (bit errors versus
signal to noise ratio in a bandwidth equal to the bit rate), you can see
the BER improves by a factor of 10 to 1 for every dB in S/N ratio. In
other words, for every dB improvement, you get one tenth the errors.
73 de Bob N6RW
On 2/25/2016 9:40 AM, donovanf@starpower.net wrote:
The weak signal CW recordings on AB7E's website are well worth
a few minutes to listen to. His recordings clearly demonstrate
-- much more convincingly than any other demo I've ever heard--
the significance of one dB of improved signal strength and the cost
of sending too fast under weak signal conditions
http://www.ab7e.com/weak_signal/mdd.html
My takeaways from his recordings:
- its well worth the effort to improve your signal by as little
as one dB
- when signals are very weak, sending faster (especially
at speeds faster then than 30 WPM) costs the equivalent of
many dB of reduced signal strength.
If you haven't already clicked on AB7E's webpage, these are
direct links to several of his recordings.
A weak CW signal buried in noise with the signal strength
decremented in one dB steps,
http://www.ab7e.com/weak_signal/6_5_4_3_2_1_0_db.mp3
Two weak CW signals buried in noise -- slightly offset in
frequency -- with one signal one dB stronger than the other:
http://www.ab7e.com/weak_signal/A_vs_B_1db_v1.mp3
http://www.ab7e.com/weak_signal/A_vs_B_1db_v2.mp3
Two weak CW signals buried in noise -- slightly offset in
frequency -- with one signal two dB stronger than the other:
http://www.ab7e.com/weak_signal/A_vs_B_2db_v1.mp3
http://www.ab7e.com/weak_signal/A_vs_B_2db_v2.mp3
CW signals sent at 20, 25, 30 and 35 WPM when buried in noise.
http://www.ab7e.com/weak_signal/A_vs_B_2db_v2.mp3
73
Frank
W3LPL
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