"Craig Markwardt" wrote in
message news

"ralph sansbury" writes:
But the cd copies of the tapes which I guess you have
access to have problems or at least the copy nasa sent me.
The cd that nasa sent me has data on it that does not
correspond to the TRK-2-25 documentation.
I did a hexadecimal dump of the first file.
The first 32 bits of file "87037.dat" are zero and the next
eight bits are 3F=0011 1111.That is the next 4 bits are
decimal

Given the garbled and fragmentary nature of the program you
posted, it
is likely that you have a software bug.

As I said that was the program used to get the dump.

The ATDF files I have are
identical to those available on-line for download at NSSDC.
(example:
87037t071.dat = 9209088 bytes). A hex byte dump of the first
16 bytes
is:

00 00 00 00 80 00 00 00 0a 05 70 05 b1 10 12 14,

exactly as expected.

In your notes you say you obtained this directly from the tape so
it may be that in transferring the tape bytes to the cd that
something happens to produce 3F instead of 80 etc.
The point is I would like to obtain the data you obtained and
before you filtered it and I would like a program and compiler to
read it.
Or better yet just use your programs to extract from the
tapes the unfiltered received doppler counter number and the
date and time for 87 and 88 as integers or ansi characters
suitable for input to an excel spreadsheet and send me the cd.



Not according to George: the local oscillator in the phase
locked loop does not produce an exact match of
the intermediate oscillation version of the received
oscillation. Rather it produces a similar oscillation where
the rising crossings of zero dont always match but
on average

If it is locked in, the loop must detect every cycle. That is
the very definition of "locked." Your requirement of an "exact"
match is irrelevant to that definition.

But as you see from George's reply here the 'detection of every
cycle' is too vague.
The real definition seems to be there are the same number of zero
crossings as the
voltage rises in a 33 minute period but not an exact
correspondence.



Your scenario of 50% missed cycles is
clearly out of lock. With the system used, telemetry can't be
received until the loop has locked onto the carrier.


If missed cycles means that there are two local oscillator
rising zero crossings before there is a intermediate received
frequency rising zero crossing then this could be made up by
three intermediate received frequency rising zero crossings
during the same time interval there are two local oscillator
rising zero crossings and then one repetition of this etc..
That is over a long enough period eg 33 minutes the average
number of zero crossings in both cases will be the same and yet
clearly there is a lot of noise in the received frequency and
other candidate frequencies with or without their harmonics
might produce the same degree of "lock".


What do you mean by overlapping uplinks and downlinks.?
Do you mean that the assumed time of downlink occurred at the
same time as an uplink but not at a later time when the
downlink
from this uplink was expected?


I will say this once more. There were cases where uplink
sessions
overlapped in time with downlink sessions, and other cases
where there
was no overlap.
It is not clear at all what you mean by overlap(complete
or partial?) or consistent. Since all scheduled sessions of
typically four hour durations involved simultaneous transmission
and reception and complete overlap what do you mean by cases
where this did not happen. How do you know there were cases where
there was no uplink during the downlinks?
One- invalid- way would be to point to bad received data at
times that implied that there might not have been an uplink at
the assumed earlier uplink time and site.
If there were valid cases of downlinks when no transmission
was going on then I would expect the data received at this time
to be noise.
And it is not obvious that some sort of spurious lock could
occur in these cases and that doppler noise and slipped cycles in
the data which you said in your notes that you did not understand
may indicate this.



I analyzed all of this data together, without regard
to the overlap, and the results were entirely consistent.


"Overlap"
is a description of whether uplink and downlink activities were
happening at the same time or not, period. Absolute uplink and
downlink epochs are not "assumed," they are measured precisely.



Nowhere did I say I got rid of data because of overlapping
sessions,
because in fact I kept it.



What do you mean by incoherent tracking sessions. This
is
just jargon for rejecting data not conistent with light
travel
time assumptions.

No. Non-coherent sessions happen when the spacecraft uses its
own
oscillator, which is susceptible to temperature induced drifts.
These
types of sessions are useless for radiometric tracking because
the
clock drift cannot be disentangled from any Doppler-induced
frequency
drift.


That makes sense.

I see the assumed transmitter frequency which you said
was
constant and which in your filter files that I have seen is
always the same although you also say that it can change.??

The uplink frequency can be ramped, but wasn't. The uplink
frequency
was constant for each session.

George and Craig, The point I am trying to make here is
that
different frequency functions may fit the received periodic
waveform regarded as noise plus a specific doppler shifted
version of the know uplink frequency.

The waveform is sinusoidal, so your point is irrelevant.

I doubt that the recieved oscillations of voltage from the 8
Watt transmitter a billion miles away is as 'sine like' as the
local oscillator in the Phase Locked Loop.
The difference between a pure sine mixer oscillator frequency
and the received frequency may be more sine like than the
received frequency but maybe not.


That is even though the best fit is given by the phase
locked
loop local oscillator frequency etc., various nearby
frequencies
alone or in conjunction with some harmonics could in fact be
the
true received periodic oscillation..

Which frequencies or harmonics? How can harmonics be "nearby?"
(they
cannot)
Obviously I mean the harmonics of neaby frequencies

Can you provide (even) a single example? All of the downlink
power spectra I have seen have been flat except for one peak.

But how wide is the peak? To say that a Doppler shift of so
much has occurred and that a Doppler shift of a slightly
different value has not occurred you need to have a very sharp
peak.
Also the lack of exact matching zeros in the PLL oscillator
and the intermediate received frequency suggests a problem but
maybe not. I wish you or George make a clear, cogent argument
that this lack of matching is not "relevant".
Ralph