[Lowfer] WD2XES WSPR Again

[Stewart Nelson]

> yes, an MP3 player is small and cheap but how good is the MP3
> compression algorithm? I don't know how it works but there are many MP3
> encoders with a lot of compression options. Is MP3 able to convey the
> sub-Hz accuracy required for some modes?

AFAIK the frequency error of a typical MP3 encode/decode is zero, although
of course, the playback hardware has an imperfect timebase, the errors of
which I've already discussed.

MP3 compression works by splitting the data into multiple frequency bands,
and coarsely quantizing (or discarding altogether) those bands with little
energy.  In this application, the effect is to add some noise, which results
in spurious lines in the output spectrum.  IMO, these are very unlikely (in
a QRP beacon) to be strong enough to interfere with other services, although
they could interfere with attempted weak signal reception of nearby
frequencies at your QTH.

A DDS-based exciter would also have some spurious output; some detailed
analysis or measurements would be needed to tell which method was cleaner.

73,
Stewart KK7KA