[GPS_Standard] What is the effect on the accuracy and speed stabilization should use the 10th harmonic

[saper]

I do not have much time so I'll stop only get 100MHz of 10th harmonic.
Yes amplification is necessary, so it is not so trivial, but it's not 
quite as difficult. Trick at the time of the pulse duration d = 45 ns.
After all, here you have a practical implementation with some theory,
http://www.eos-optronics.com/documents/Paper-200MHz_Multiplier.pdf


On 11.03.2013 06:02, Dave Platt wrote:
> On 03/10/2013 09:32 AM, saper wrote:
>> I have a 10MHz OCXO MV89. Getting from 10MHz 100MHz, using the 10th
>> harmonic
>> MV89 sinus -> PECL nomparator make square 45/65 -> high quality
>> band-pass filter 100MHz -> ERA amplifer -> high quality band-pass 
>> filter
>> 100MHz.
>> My question is simple
>> Somehow affects the accuracy and speed stabilization, when the 
>> feedback
>> instead of the basics 10MHz will use 10tj harmonics 100MHz?
>> I would counter implemented in FPGA.
>
> Well, I'm going to go on intuition here - I may be right or wrong,
> but in either case I don't have direct experience with this sort
> of setup nor can I offer a mathematical proof of what I suspect.
>
> My suspicion is that this may be a somewhat tricky thing to do,
> with some odd quirks.  Getting a strong, clean 10th harmonic out
> by this sort of arrangement might not be easy.  The Fourier
> expansion of a square wave consists of the sum of *odd* harmonics,
> not even.  You'll probably get *some* 10th harmonic content, but
> it's not likely to be a strong one - you'll need a good deal of
> amplification, and noise may be a significant concern.  Using
> a comparator threshold to give you a nonsymmetrical result will
> add some second-harmonic content but I'm not sure that you can
> count on a useful increase in higher-even-order harmonics such
> as 10x.
>
> As far as timing stability goes... if you're planning on running
> the FLL counter from the amplified 10x harmonic, I'm concerned
> that you may have some problems with jitter.  In effect, what's
> going to be happening (I think) is that you've got two high-Q
> bandpass filters which will "ring" at 100 MHz, when excited by
> an incoming burst of 100 MHz content (the 10th harmonic of the
> OXCO) which is likely to occur mostly at the rising and falling
> edges of the squared-up comparator output.  The tricky bit is
> that the two bursts of 100 Mhz impulse are *not* guaranteed to
> be in the same phase relationship with one another (I think).
>
> That is:  on the rising edge of the comparator, the BPF
> will be "kicked" into ringing by the 10th overtone of the
> OXCO.  This ringing will decay somewhat during the time
> when the comparator output remains high (the amplitude
> of the 100 MHz signal will decrease).  Then, the comparator
> output will go low, "kicking" the BPF again... but this
> second "kick" is likely to be out of phase with the
> remains of the original "ringing".  This will cause
> some amount of jitter (in effect a modulation) of the
> 100 MHz output from the second BPF.  When the comparator goes
> high again, the same thing will happen... a "glitch" in the
> amplitude and phase of the 100 MHz signal will occur.
>
> So, if my hunch is correct, your 100 MHz signal is likely
> to have a significant amount of phase noise on it... more than
> was present in the original OXCO.  This might have some effect
> (probably small?) on the FLL pulse-counting system... it'll
> probably become negligible if your averaging time is long enough.
>
> Another approach to getting a 100 MHz signal, would be for
> you to use a PLL circuit with a 10x divider to generate the
> 100 MHz signal.  This would give a strong, clean signal - less
> chance of low-level noise because you won't need a
> harmonic multipler / BPF system.  PLLs add their own types
> of jitter, though.
>
> I guess I don't see why pulse-counting the 10th harmonic signal,
> would give you any better stability or accuracy than just
> pulse-counting the 10 MHz OCXO fundamental.  It might well be worse.
> *Anything* you do to create the 100 MHz signal from the
> 10 MHz OXCO output is necessarily going to involve processing
> and manipulation of the 10 MHz signal, adding noise of one
> sort or another... and you might have to increase the averaging
> period of the FLL to filter out the effect of this noise, thus
> nullifying any benefit you might hope to achieve by pulse-counting
> a faster-clocked signal.
>
> That's what my intuition is telling me.  If anybody can prove me
> wrong, or can confirm that I'm right... I'm very interested in either
> case!
>
>
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