What Use Is An F-call?

What use is an F-call? You're 5 and 9, or 20 over 9, or 5 and 5. It's a phrase that you'll hear regularly in amateur radio conversations as you tune up and down the bands. If we ignore for a moment the readability signal, the first number, in this case "5", which I have to confess is pretty arbitrary. My perfect readability is not going to be the same as yours. The deafer I am, the less likely you're going to get a readability score of "5", lets look at the second number. It's a signal strength. Pretty straight forward. It goes from S0 to S9 and sometimes there are extra decibels added, 10 dB over, or 20 dB over, etc. The S meter in your radio is actually a very sensitive micro ammeter. The dial displays in S-units. What is an S-unit? Well, until 1981 there wasn't a real standard. In the 1930's they'd decided that S9 means 50 microvolts at the input of the receiver, but there wasn't a standard impedance of 50 Ohm, which we take for granted today, so the number is pretty meaningless in