wrote:
In article ,
says...
wrote:

I think it is more like a long train (2 seconds long) on a short
U shaped track (1.25 seconds on each leg). The engine coming
back will pass the caboose still on its way to the end of the U.

An interesting and thoughtful response. However, it generates a
question:

In your train analogy above, what is to keep the leading part of
the echo from being QRMed by the trailing part of the transmitted
signal?



The analogy is good in so far as it shows the timing, but I have to
admit it is poor in that I used a solid object, the train, to
represent a wave and their properties are very different. For
example, if two trains hit head on, you are going to have a mess.
That is not the case with waves. If you throw two rocks at the same
time in a pond of still water so that they land some distance apart,
the waves from each impact point move out in concentric rings. When
the rings from one impact point spread out enough to meet the
spreading rings of the second, there is however no "wreck". The
rings of waves of one appear to pass through the rings of the other
with no harm done to either wave.

I don't think that is true. I believe the waves would add, subtract or
be somewhere in between depending on their phase relationship.

It is the energy that is moving across the water, not the water.

Here is a good URL for seeing a wave reflecting.

http://www.bbc.co.uk/schools/gcsebit...ater_wavesrev3.
shtml

(http://tinyurl.com/2ykkdr)

In our case the pulse is much longer so the interaction is longer,
and it also is not physical water, but the wave theory is the same.

What you say is interesting, but...wave theory notwithstanding, what we
have are TWO RF signals on -essentially- the same frequency (ignoring
Doppler, libration, etc), the incident and the reflected. And I think we
both agree that the signals "overlap" for .75 seconds (as so aptly
stated in your 'train' analogy). Just like the old USSR jamming the VOA
-- two signals on the same frequency. Why wouldn't they interfere for
the .75 seconds in question?

Let me give you one more analogy:

Assume the moon is -totally- absorbent (no RF reflections).

Next assume an earth station sends a 2 second long 7.0000 MHz CW signal
towards the moon.

Finally, assume there is a radio operator on the moon. The -instant- he
hears the earth signal, he turns on -his- 7.0000 MHz CW transmitter.

Again, because of the 2 second earth signal and only a 1.25 second
transit time, the two signals will overlap by 0.75 seconds.

How can they NOT interfere with each other for the .75 second overlap?
This is -exactly- like SWBC jamming (only unintentional) and all the
'wave theory' in the world doesn't mean jamming doesn't work. Sorry, but
I believe two signals on the same frequency during the same period of
time will interfere with each other.