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8

First, some history. As I understand it, the "dit-dit" (E E) comes from an old practice. There is a short tune in popular music that was often used to end a musical performance in a humorous way, called "shave and a haircut, two bits". The Wikipedia article has a recording of the tune. For older people, the rhythm of the notes in the tune is instantly ...


5

The dit dit that is sometimes (not all the time) sent at the end of a QSO is a derivitive of the old time "shave and a haircut -- two bits". Back when I was a novice on the 40-m band in the 1960s it was quite common for the final signoff (whomever that might be) to send "dit di-di-dit dit" and the other operator would then respond with "dit dit". However ...


2

The answer can be fond in The ARRL Handbook 2019, Vol 3, although it's spreaded across different chapters. In short, SNR is typically calculated for the noise floor of 2500 Hz SSB signal. Particularly this is how WSJT-X calculates negative SNRs for FT8 and other modes. Now the trick is that by deviding the bandwidth in half you decrease the noise floor by 3 ...


4

Probably ease of detection, or using the known OOK signal as kind of a frequency-synchronization and rate-synchronization method. It's hard to tell – in low-power and least-cost electronics, the emphasis often is not on RF signal optimality, but in ease of production and power usage, things you won't find out without knowing the silicon design process. It ...


4

That was a Morse code message, using common abbreviations to save time. Here it is translated into plain language: [CQ=] Calling any station, [de=] from radio station KYHP. [QTC?=] How many telegrams have you to send? [K=] Go ahead, I'm listening. The first letter K means that the station was a US station; however, it may or may not have actually been ...


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