In article <3F195CF6.B74DE25D@xmission.com>, rom: red <read@xmission.com> wrote:

	0 Hz (no Doppler shift) usually means that the source and receiver are

The reference was to 0Hz/s (dimensions time ^ (-2)) not to Hz (time ^ (-1)).
Because it doesn't know the intended transmit frequency, S@H can only consider
rate of change of Doppler shift, not the absolute value.

stationary, relative to each other; almost certainly the source is on or

0 Hz/s means they are not accelerating, not that they are not moving,
relative to each other.

near Earth.  A geo-stationary satellite *could* produce that result, but it

Agreed.  (Geo-stationary satellites are actually accelerating earthwards, but
their range rate is not changing, and it really the derivative of range rate
that matters.)

probably would not be spikes.  A transmitter on the Moon *could* also do
this, if there even was one, and the Moon was in the Arecibo Radio
Telescope's Field of View (FOV).

An uncorrected transmitter on the moon would chirp at close to the
pre-compemsated chirp rate due only to earth rotation and would, probably
be a strong candidate from a chirp rate point of view.  (Incidentally,
moon reflections of terrestial signals are quite likely to have that
characteristic as they are quite likely to be from the limb of the earth,
where the Doppler shift is maximum, but the chirp minimum..