![]() The moving average is very good at detecting the edge of a pulse such as the 1 second tick transmitted by WWV. The resulting signal is then power detected and low pass filtered with a filter called a moving average filter. The sampled signal is filtered and reduced to a sample rate of 1000 by a process called decimiation in time. Most modern soundcards will use 44100 or 48000 as the native smampling rate. This block sampling is what sets the basic timing mechanism for the thread that reads the sound card. The sound card samples the signal and returns a block of samples in blocks of 512. The sampling rate for the sound card should be set to "native". It does this by comparing the sound card sample rate with the clock tick signal that is transmitted by WWV and WWVH. The WWV mode is used to measure the offset of the sound card oscillator. European and Asian users should be able to use the German DCF-77 or Russian RMW time transmissions. Operators in the North American region can use the WWV and/or WWVH standard time transmissions for this purpose. ![]() The best way to insure that they are identical is to calibrate both to an external frequency and time standard. Some analog transmissions such as FAX, MFSK images, and Thor images will exhibit a slant in the received image if the sound card clock (sample rate) is not identical at both the transmitter and receiver.
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