Re: Question For Craig Markwardt re Pioneer 10 Data

"George Dishman" <[EMAIL PROTECTED]> wrote in message
news:[EMAIL PROTECTED]
>
> "ralph sansbury" <[EMAIL PROTECTED]> wrote in message
> news:[EMAIL PROTECTED]
> > George, I know you are a superior EE and that
>
> I like the word "adequate" in that respect.
>
> > you understand or at least can imitate the jargon in the nasa
> > documentation.
>
> I understand most extremely well, I tell you when there
> is something I don't understand.
>
> > But you and nasa are talking to EEs and not to an audience
> > that has some elementary understanding of electrical circuits
> > and basic physics.
> >    I am trying to represent this in a way which is
intelligible
> > without going into details that obscure the basic procedure
> > and why it is reliable.
>
> Understood.
>
> >    I am surprised at your  lack of understanding of this
> > and general lack of good will.
>
> Let me put it this way. Suppose I tried to explain America
> to you and said "it is a land where all are equal" and you
> said "that's too difficult to understand, I'm going to call
> it a dictatorship, it's close enough because both are
> political systems". Would you think that reasonable? It is
> what you are doing.


I think you are exagerating.

> > > "ralph sansbury" <[EMAIL PROTECTED]> wrote in message
> > > news:[EMAIL PROTECTED]
> > > >
> > > > "George Dishman" <[EMAIL PROTECTED]> wrote in
message
> > > > news:[EMAIL PROTECTED]
> > > > > Hi Ralph,
> > > > >
> > > > >
> > > > > Where did you read that it was a dual gate transistor?
> > > >
> > > >     It is surely more complex than this but this is the
principle
> > > > used in obtaining an intermediate frequency.
> > >
> > > OK, the principe used is multiplication.
> >      No the principle is what I said. The law of
superposition suggests
> > electrical fields are added, not multiplied.
>
> Lets write down some voltages for a mixer with two inputs
> and an output. This is "in principle", actuals signal
> levels are much smaller:
>
>  V_a    V_b  V_out
>

> This is a multiplication table. Superposition doesn't mix
> the signals, you have to build something special to do it.
        Superposition is what occurs first. Then a filtering
process. I have explained this because you evidently cant..
>

> > When you say something
> > like this you should also say that the sum of sine  functions
etc can
> > be represented as a product of related sine functions etc.
>
> You already know that so I don't need to say it again.
    But it appears you dont know it and that it is essential to a
clear explanation.

 Anyway
> it is not relevant to the fact that a mixer takes voltage V_a
> and voltage V_b and produces:
>
>   V_out = V_a * V_b
>

   It is very relevant. Your shorthand only makes sense to some
adequate EE like yourself.

> >  A dual gate
> > > device is one way of producing multiplication but is
> > > very specific and quite possibly incorrect.
> >
> >       Watch your language. Your are contradicting yourself.
> >  You mean inexact, it is correct in principle as you just
said.
>
> I mean 'incorrect' in that they may be achieving multiplication
> but not using a dual gate FET.
       Of course. But a dual gate transistor is a simple way of
getting the idea across to dummies like me.

 If you say "multiplication" it
> is non-specific and correct, saying "dual gate transistor" is
> specific and may be wrong because they may be using a set of
matched diodes or something completely different.

 But it is correct in principle and that is what we are talking
about here.

> >     Please explain how a mixer works if it does not contain
one sort
> >  of tuning  to get the difference frequency.
>
> Tuning means selecting one frequency from many. The mixer works
> by multiplication

   You are now talking about a different circuit than the one I
was. And you dont really describe how the multipication is done
yet.

 of two voltages, one is the reference and the
> other is a wide band signals with many frequencies. The result
> contains sum and difference frequencies as two wide bands but
> these are also separated by a gap.


 The result is filtered, not
> tuned, to discard one entire wide band but retain the other
> entire wide band.
>
> Suppose the signal is a band from 2265MHz to 2375MHz and it
> is multiplied by a pure sine wave of 2000MHz. The sum is a
> band from 4265MHz to 4375MHz while the difference is a band
> from 265MHz to 375MHz. To get just the difference, all you
> need is a simple filter that rejects anything above say
> 1500MHz but lets through everything below 500MHz with equal
> gain (between 500MHz and 1500Mhz, the gain can fall gently).
>
> > out of the superposition or combination of the input
frequencies, another
> >  sort to get the sum frequency, another sort to get the
single
> frequencies.
> > By tuning I mean a resonant inductance and capacitance to
tune or filter
> > out all but the chosen frequency
>
> That is the correct meaning of 'tuning' in this context. The
> point is that this is not done in the system, they work with
> wide bands of frequencies and treat them with equal gain, so
> cannot use tuning.
>
> > or perhaps striclty capacitive
> > high and low pass filters.
>
> That is correct but very different. One filter might pass
> everything above 250MHz equally but have a rapidly diminishing
> gain below that. The other would pass everything below say
> 400MHz equally and have a rapidly diminishing gain above that.
> In the region of interest, the gain is constant over all of the
> band of frequencies.
>
> > > > and if there is a
> > > > digital version here, then feel free to explain it. I did
not
> > > > understand your email explanations.
> > > >
> >         Please answer this question.
>
> Sorry, I thought I had replied to that. The mixer is
> analogue, not digital. Maybe it was in another reply.
> My email explanations related to the later stages after
> the signal is digitised.
>
> > > > > > picks out the difference frequency and a a
> > > > >
> > > > > Wrong, it doesn't pick out one frequency, it passes a
> > > > > complete band of frequencies to the FFT.
> > > > >
> > > >     OK relax. It is a small band of frequencies around
the single
> > > > difference frequency. This is always understood.
> > >
> > > No, it is a very _wide_ band of frequencies selected out of
> > > an even wider band as shown in the diagrams:
> >
> > We are talking about the size of the intermediate frequency
range
> > relative
> > to the original range  1MHz is small relative to 200MHz but
not
> > to 1Hz
>
> The terms "narrow band" and "wide band" compare the width
> of the equipment to the width of the signal being processed.
> Wide band in this context means sufficiently wide that it
> does not exclude any frequency of interest or produce any
> modification of the signal such as emphasising one frequency
> more than another.
>
> > > > > > sequence of voltages at this difference
frequency.(mixer
> > and
> > > > > > repeated heterodyne up and down conversion etc is the
> > jargon and
> > > > > > the engineering details I am trying to avoid).
> > > > >
> > > > > Instead you are inventing a process that doesn't exist
> > > > > and describing it in far more (and incorrect) detail
> > > > > than exists in the published documentation.
> >
> >          As I have detailed above you are misunderstanding
what I
> > am saying
>
> What you are saying is very different to what is being
> done. It may be that this is because you are using terms
> in an unconventional manner but you will then hit problems
> in referring to your text books.
>
> > > >     If you understand by difference frequency a small
band around
> > > > a specific difference frequency then there is no problem.
> > This is
> > > > obviously the meaning of what I have said.
> > >
> > > I know, but it is wrong. It is not a small band, it is
> > > a wide band.
> >       1MHz is small relative 200MHz but not to 1Hz. Obviously
> > that
> > is what is  meant here when we are talking about the
reduction of
> > the sky frequency to something that is more amenable to
analysis
> > And the reason this is possible is that the difference
between
> > the lower
> > frequencies is the same as that between the higher.
>
> I don't quite follow that. The examples frequency bands
> I gave above may clarify the situation.
>
> > > > > >    This sequence of oscillations is digitized into a
set
> > of 1s
> > > > >
> > > > > The entire band is digitised.
> > > >
> > > >    It is clearer to say that the observed sequence of
> > > > oscillations is digitized.
> > >
> > > Again it may be clearer but it is wrong. It is not just
> > > the carrier oscillations that are digitised, it is the
> > > whole signal, oscillations plus random thermal noise
> > > and any other sources such as the galactic background.
> > >
> >    Your understanding is wrong. I did not say CARRIER
> > oscillations
> >  You can't change the  meaning of
> > 'oscillations' to mean  only the
> > part due to the spacecraft transmitter
>
> "oscillations" means something regular, the noise is
> random so not regular in any way and that is critically
> important to extracting the signal. Your use of the word
> is inappropriate and confusing.
>
> > I accept your apology but maybe you are similarly misreading
> > the nasa documents and that is why you are missing the
essence
> > of the procedure. You cant see the forest from the trees.
>
> NASA don't talk of 'oscillations', they correctly talk of
> the signal.
>
> > > > > > and 0s (1 if the analogue voltage is above a certain
> > amount etc)
> > > > > >  and an Fast Fourier Transform  procedure is used to
find
> > the
> > > > > > underlying "sine" pattern of 1s and 0s that most
closely
> > fits
> > > > > > this.
> > > > >
> > > > > Nope, the amplitude of _all_ frequencies in the band is
> > > > > calculated and passed on to the next stage without any
> > > > > judgement.
> > > >
> > > >      I am talking about the final stage
> > >
> > > The final stage is the carrier PLL, not the FFT. All
> > > the FFTs are removed from the chain once the PLL locks
> > > on and they play no further part in the process. It is
> > > the PLL that tracks the drifting signal and gives us
> > > the accurate measurement.
> >
> >     The FFT  as I was using the term includes the PLL.
>
> The two are entirely diffeent and separate.
>
> > The point
> > which you insist on obscuring is that this technique
> > gets at the right sine frequency starting at the right time
from
> > the
> > sum of sine functions of various frequencies equivalent as
> > Fourier showed to
> > the noisy oscillations observed.
>
> You said "an Fast Fourier Transform  procedure is used to find
> the underlying "sine" pattern of 1s and 0s that most closely
fits"
>
> The FFT is not applied to "1s and 0s", it is applied to voltage
> samples. The frequency is found and the PLL commanded to start
at
> that frequency. The PLL locks on and tracks the carrier and it
> uses a digital phase comparator that probably treats the signal
> as 1s and 0s.
>
> There are several levels of processing that you are skipping
over
> which are very important in establishing that the signal is
> genuine and from the right craft. Ultimately that is your main
> concern, isn't it?
>
> > > > and I mentioned that the
> > > > movement of the Earth etc requires different patterns to
be
> > > > obtained successively but the point is that the FFT
procedure
> > > > finds the underlying pattern and it is this that is used
to
> > > > compare to the given sequence of 1s and 0s.
> > >
> > > No it isn't. The final FFT is only used to set initial
> > > frequency for the carrier PLL. If that locks, the
> > > bandwidth is reduced to improve the signal/noise ratio.
> > >
> >
> >       You are saying the same thing that I was saying. I
think
> > it is clearer to say it without the jargon.
>
> Clearer but completely wrong. The FFT does not compare
> anything to a pattern of 1s and 0s. It does not compare
> anything to anything else and in this case it does not
> work on 1s and 0s.
>
> >  The output of that is fed to the sub-carrier PLL.
> >
> >     Whatever the details  a sequence of 1s and 0s
> > is obtained that is a digitised intermediate version of the
> > sky frequency.
>
> No, a series of voltages samples like +0.25, -0.375, +0.112
etc.
> is the result of digitising the IF.
>
> >  Again
> > > that has to lock before the signal can be decoded using
> > > a phase detector. Then it gets decoded through the error
> > > correction scheme. There are many critical steps after
> > > the FFT, and in fact the FFT plays no part in the decoding
> > > process whatsoever.
> >
> >     The bottom line is a sine representation of a sum of sine
frequency
> represention
> > of an oscillating pattern made possible by the FFT procedure
essentially
> > and this includes the phase locked loop procedure perhaps
involving
> > the recognition of some code modulation of the carrier  to
insure that
> > the fitted frequency starts at the right time.
> >
> >
> >    The fact that this representation is a much smaller
frequency than
> > the GHz sky frequency is ok because when you look at the
difference
> > between this and a small frequency representation of the
transmitted
> > frequency the difference is the same as the difference
between the
> > original frequencies. And it is this difference that is used
to
> > get the
> > Doppler shift.
> >
> >
> >
> >
> > > >    This is the procedure I understood from your comments
and
> > > > various books and links.
> > >
> >
> > > >    Ralph, it's as if all the weeks I spent
> > > > > talking you through the DSN documentation by email had
> > > > > never happened. You seemed to grasp it at the time, why
> > > > > have you reverted to this grossly inaccurate
description
> > > > > of the process?
> > > >       Again I think you have misunderstood what I have
said.
> > I
> > > > dont think it is inaccurate if you replace single
> > intermediate
> > > > frequency by small range of frequencies around the single
> > > > intermediate frequency where small is relative the
original
> > frequency.
> >
> > >
> > > It is very inaccurate when the DSN document tells you
> > > the analog band is the digitised band is 110MHz wide and
> > > the signals of interest are of the order of 1Hz wide.
> >
> >     You are quoting the wrong document. We are talking about
the
> > intermediate frequency
> > being smaller that the original frequency. Is that so hard
for
> > you to understand.
>
> What matters is how wide the frequency range is compared
> to what you are looking at. If the equipment only handles
> a band that is small in comparison to the signal, the edges
> will be chopped off, or if the Doppler shift was more than
> expected the signal might be lost entirely. If th system
> is 'wide band' then there is no such risk. How wide it is
> compared to the original is completely irrelevant. Now this
> matters because I know you are rferring to text boks and
> those will use "wide band" and "narrow band" as terms relating
> the width of the channle to the width of the signal, so if
> you look up the text for "narrow band", you are going to get
> entirely misleading information.
>
> > I am continually amazed that a person of your knowledge and
> > intelligence has so many
> > blindspots.
>
> On the contrary, I can see potential mistakes you are
> about to make through your unfamiliarity with the jargon
> and I am trying to educate you in these terms to avoid
> those pitfalls before you reach them.
>
> > > >    And if you want to try and describe the digital
version of
> > the
> > > > mixer please do so. It was not clear from your emails.
> > >
> > > The mixer is analog. The output is digitised and a baseband
> > > extracted as shown on page 10. The details of the method
> > > of mixing are not given but the principle is simply
> > > multiplication of the incoming signal (including noise) by
> > > the reference sine wave.
> > >
> > >  V_out = V_in * V_ref
> > >
> > > where
> > >
> > >  V_ref = A * sin(wt)
> >
> >    This makes no sense. Electrical oscillations add by the
law of
> > superposition;
>
> Yes, which is why it takes a special ciruit to get around that.
>
> >  Tthey dont multiply.
>
> Dual gate fets and other methods of implementing mixers do
> because that is their intended function and we poor designers
> have to make them do it well. It's what engineers  get paid
> for (though I personally work on the digital side).
>
> > The mathematical fact that a sum of sine
> > and cosine functions can
> > be represented as a product of related sine and cosine
functions
> > has to be mentioned dont you think?
>
> Only if you don't already know it. The circuit multiplies
> the two voltages together and since the product is the
> same as a combination of sum and difference, you can then
> discard all of (say) the sum components and keep all of the
> difference components by a simple filter. Tuning is not
> required, highly undesirable, and is definitely not included
> in that part of the DSN system, it uses filtering instead
> and to remove the jargon, that means it doesn't select a
> single frequency from a range, it accepts the whole range,
> treats it all equally, and only rejects a mirror image of
> the range very far away.
>
> George
>
>