Ken S. Tucker a écrit :

Posted to spr.

FrediFizzx wrote:

"John (Liberty) Bell" <john.bell@accelerators.co.uk> wrote in message
news:1156592712.626510.96920@p79g2000cwp.googlegroups.com...

In the Pioneer 10 mission, the ability to maintain communication was
extended to larger distances post launch, by the substitution of a
lower noise preamplifier in the pedestal unit. Despite this, it looks
like noise was still the reason why communication was eventually lost.

Does anybody know whether such remaining noise was still predominantly
electronic noise generated in the improved preamp, or external noise
picked up by the dish?

I hope that the reason for asking this question is obvious. If the
answer is still preamp noise, then space missions could be taken to
still greater distances, and for longer durations, simply by further
improvements in preamplifier design.

I would think that transmitter power and bigger antennae would be a
greater factor than improved preamp design as far as distances and
durations are concerned. I expect that preamp design by now is pretty
close the the theoretical noise factor limit.
FrediFizzx

I was a "b" grade designer of receivers in the mid-80's.
What we focused on was a very sharp "Q" factor,

http://en.wikipedia.org/wiki/Q_factor

The idea being the noise is directly proportional
to bandwidth, so the larger the bandwidth, the
greater the required Signal to Noise ratio "S/N".
The Signal is increased by more Transmission
Power (Tx) or a better antenna and gain system
(Rx), as Fred points out, but the noise is reduced
by a sharper Q-factor, correct me if I'm wrong.

I do not know the limits to the Q-factor, but let's
suppose +/- 1 hertz at say 100 Mhz might be
achieved with good design, that's a guess.
In the case of inter-planetary travel, the Tx and Rx
are finely tuned, (1 part in 10^8th) so effects such
as "gravitational red-shift" and "Doppler shift" need
to be calculated and assuming the Tx is based
on some standard, like an atomic clock, then
the Rx reception frequency will need to be fine
tuned throughout the mission. That fine tuning
can provide navigational information about the
effects of relative gravitational potential and relative
velocity, in proportion to the sharpness of the Q.

Recall that astromomers would use a long-term
exposure to capture faint images that the eye
could not see in real time even in large telescopes.
That, I think, is an example of using a "sample
time", (the exposure duration) to integrate the
signal, in that case, in visible radiation band.
We found similiar techniques could be applied
to radio bands of very high Q.
For the electronic savvy, the procedure was to
adjust a well designed "Super-Regenerative" detector,
to charge a capacitor to pulse at say once/sec,
strictly due to noise.
A high Q Tx on the "SR" detector frequency
would vary the pulse to once/.9 secs indicating
a sent 1 bit.
Obviously, it takes time to transmit and receive a
message that way, but if not in a hurry it works,
just like a long duration astro photograph does.
Regards
Ken S. Tucker

I have a question also Ken

You mention that the Tx frequency had to be based
on a standard (of course), like an atomic clock.

Do you know for a fact that it was based on an atomic
clock?

Sub question: if so, I assume it was an atomic clock
located at ground level. Then has anyone thought of
doing the calculation with an atomic clock operating
from orbit (in the ISS for example)?

André Michaud

Ken S. Tucker a =E9crit :

Posted to spr.

FrediFizzx wrote:

"John (Liberty) Bell" <john.bell@accelerators.co.uk> wrote in message
news:1156592712.626510.96920@p79g2000cwp.googlegroups.com...

In the Pioneer 10 mission, the ability to maintain communication was
extended to larger distances post launch, by the substitution of a
lower noise preamplifier in the pedestal unit. Despite this, it looks
like noise was still the reason why communication was eventually lost.

Does anybody know whether such remaining noise was still predominantly
electronic noise generated in the improved preamp, or external noise
picked up by the dish?

I hope that the reason for asking this question is obvious. If the
answer is still preamp noise, then space missions could be taken to
still greater distances, and for longer durations, simply by further
improvements in preamplifier design.

I would think that transmitter power and bigger antennae would be a
greater factor than improved preamp design as far as distances and
durations are concerned. I expect that preamp design by now is pretty
close the the theoretical noise factor limit.
FrediFizzx

I was a "b" grade designer of receivers in the mid-80's.
What we focused on was a very sharp "Q" factor,

http://en.wikipedia.org/wiki/Q_factor

The idea being the noise is directly proportional
to bandwidth, so the larger the bandwidth, the
greater the required Signal to Noise ratio "S/N".
The Signal is increased by more Transmission
Power (Tx) or a better antenna and gain system
(Rx), as Fred points out, but the noise is reduced
by a sharper Q-factor, correct me if I'm wrong.

I do not know the limits to the Q-factor, but let's
suppose +/- 1 hertz at say 100 Mhz might be
achieved with good design, that's a guess.
In the case of inter-planetary travel, the Tx and Rx
are finely tuned, (1 part in 10^8th) so effects such
as "gravitational red-shift" and "Doppler shift" need
to be calculated and assuming the Tx is based
on some standard, like an atomic clock, then
the Rx reception frequency will need to be fine
tuned throughout the mission. That fine tuning
can provide navigational information about the
effects of relative gravitational potential and relative
velocity, in proportion to the sharpness of the Q.

Recall that astromomers would use a long-term
exposure to capture faint images that the eye
could not see in real time even in large telescopes.
That, I think, is an example of using a "sample
time", (the exposure duration) to integrate the
signal, in that case, in visible radiation band.
We found similiar techniques could be applied
to radio bands of very high Q.
For the electronic savvy, the procedure was to
adjust a well designed "Super-Regenerative" detector,
to charge a capacitor to pulse at say once/sec,
strictly due to noise.
A high Q Tx on the "SR" detector frequency
would vary the pulse to once/.9 secs indicating
a sent 1 bit.
Obviously, it takes time to transmit and receive a
message that way, but if not in a hurry it works,
just like a long duration astro photograph does.
Regards
Ken S. Tucker

I have a question also Ken

You mention that the Tx frequency had to be based
on a standard (of course), like an atomic clock.

Do you know for a fact that it was based on an atomic
clock?

Sub question: if so, I assume it was an atomic clock
located at ground level. Then has anyone thought of
doing the calculation with an atomic clock operating
from orbit (in the ISS for example)?
Andr=E9 Michaud