RadioBanter - View Single Post - European Mars probe to use 80meters to look for Martian water?

August 14th 04, 12:55 PM

In article ,
(Len Over 21) writes:

It doesn't work that way, Mike. I posed the challenge and it's up
to others to answer...such as yourself.

Why not simply answer
the questions?

All the information is available to YOU. Won't take much searching
to find it.

No need for Keplerian tables or that other BS about "picking a position"
since all you need is the MAXIMUM distance for path loss.

The path loss varies
quite a bit, depending
on the positions of
the planets...

Or, you can cheat and crib from NASA information.

Why would copying
NASA information be
"cheating"?

They've been
in the interplanetary communications business for over three decades.
Theoretical information is even older, and still accurate.

Why not simply answer
the questions?

Tell us what the Doppler shift is over the length of a short QSO,
starting at the time of of start Assume a DX style QSO with a short
feedback message to insure actual reception on both ends, say a 35
second transmission. Then the same for the return message.

The Doppler shift
will be essentially
constant over the
length of such a
QSO.

If the Doppler shift
is expressed as a
percentage of the
operating frequency,
it depends only on
the relative velocities
of the stations.. The
relative velocity
calculation should
take into account both
the orbital and rotational
velocities.

Illogical premise. Interplanetary QSOs have such long round-trip
times that your paradigm isn't worth 20 cents. Think about it.

Illogical answer. Len
appears not to understand
the question. This is
understandable because
Len is neither a radio
amateur nor a contester.

It has been calculated that
round-trip delay at closest
approach would be only
a bit more than 6 minutes.
This is also the time of
minimum path loss and
low Doppler shift. Therefore
the premise is quite logical.

If you understand it.

Doppler shift isn't a big problem.

That depends on
the specifics.

RF power output IS.

Not really. The
robot probes to
Mars and beyond
do not use high
power. Less than
100 watts is more
than adequate.

The use of such low
power requires the
use large but steerable
antennas and very
sensitive receivers.

In the early 1960s,
some amateurs
were allowed to use
the 1000 foot
Arecibo antenna
for amateur EME
operation.

They were quite
successful, even
with the limitations
of amateur equipment
of those times..

Think about
that...no ionosphere in between planets, nothing else like it.

Nothing else
is needed.

At this time I don't know those details, but I'll be happy to check
them out once you've posted them. Add anything I have forgotten but may
need to know.

Sorry, Mike. It's up to YOU and the other latter-day saints of see-
double-yew to take the first shot. You are NOT the range officer
in this shooting gallery.

Why not simply answer
the questions?

If you can't do it, well, you can't do it. No problem to me. :-)

It appears that Len
can not answer the
questions.

Some very rough
calculations of
path loss:

At closest approach, the one-way path to Mars is roughly about 60 times the
round-trip distance to the moon. So the path loss is 3600 times greater. 3600
times greater is roughly 71 dB.

However, the moon is a pretty poor reflector, losing very roughly about 11 dB
at typical UHF/VHF amateur frequencies. This loss would not exist on a one-way
path to Mars.

So as a very rough estimate, the one-way path loss to Mars at closest approach
is about 60 dB more than EME path loss.

These are very
rough calculations
but at least they are
an answer.