[evlatests] short shallow drops

[Ken Sowinski]

On Mon, 7 Jan 2008, Ken Sowinski wrote:

> Since the MIB updates DDS chirp parameters periodically whether commands 
> are received or not it seems that MIB-DDS communications are not the 
> culprit here.

The premise is not true, so the conclusion is unwarranted.
Barry reminded me that the chirp parameters are passed on
to the DDS, at a precise time, whenever a new command is
received at the MIB.  Without new commands the DDS will
flywheel with the last values of phase and its first two
derivatives.