10 January, 2023

Audio delay - the unspecified parameter for ham radio transceivers

Elecraft K3: Upper trace is start of sidetone and
lower trace is start of RF ~15 ms later.
An amateur radio transceiver is not a precision measurement device. This is apparent when it comes to measuring time for your own round-the-world signal or when characterizing Long-Delayed Echos (LDE). One cannot just substitute onset of sidetone for the actual start of transmission of RF. Similarly there may be an unspecified delay between received RF and start of audio output on the receiver side.  

The main specification for ham radio transceivers is that the sidetone is synchronized with the keying. The delay to start of RF is only of secondary importance. All numbers should therefore be judged against the length of a dot which for instance at a morse code speed of 30 WPM is 40 ms. 

Here are some measurements for the Elecraft K3 and K2 that I did in 2021 for a presentation on LDEs at the HamSci 2021 conference. A video of the presentation is also available: Long delayed radio echoes – the illusive secret of the ionosphere