Re: Distorted Sine Wave

On Wed, 29 May 2024 20:08:58 -0700, john larkin <jl@650pot.com> wrote:

On Wed, 29 May 2024 18:19:40 -0700, boB <boB@K7IQ.com> wrote:
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On Wed, 29 May 2024 20:49:27 -0000 (UTC), Cursitor Doom
<cd999666@notformail.com> wrote:
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On Wed, 29 May 2024 13:42:13 -0700, john larkin wrote:
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On Wed, 29 May 2024 21:43:54 +0200, Arie de Muijnck <noreply@ademu.com>
wrote:
 

On 2024-05-29 19:07, Cursitor Doom wrote:

Gentlemen,
 
Whilst fault-finding on my HP 8566B spectrum analyzer, I've found the
10Mhz reference oscillator is generating an 'unsatisfactory waveform'
which may be causing the device to be unable to lock it's main PLL.
I've come across this waveshape before, but mostly with oscillators I
was building and in the process of trying to iron out the wrinkles of
and certainly NOT a critical reference oscillator from a respected
manufacturer. Can anyone tell what's most likely going on here?
 
https://disk.yandex.com/i/z6fYbeVfPRK7aA

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Looks like reflections in the cable. Try the 50 Ohm termination.
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Arie

 
If the drive is a sine wave, a cable can't generate that 2nd harmonic.

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I don't understand how a reflection can account for it either. THe cable's
only 4' long! However, with the 50 ohm input enabled, the 2nd harmonic
disappears. It's just one of those inexplicable mysteries that no one
knows the answer to. :)
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Our boxes output a 10 MHz square wave. Our clock inputs have a 10 MHz
bandpass filter, so they accept most anything.

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Weird but I'm not surprised that  4 feet if coax, unloaded at 10 MHz
gives a strange waveform.  Can simulate this, I believe, in LTspice
using the transmission line element(s).
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Learned something here though.
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boB
AZ

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No txline can create frequency components that are not in the source.
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(Well, a NLTL can, but 4 feet of coax isn't a shock line.)
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But the problem, as usual, is underspecified. Maybe some driver is
going nonlinear. A schematic would help.
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I was thinking the same thing.  Non-linearity.

But he said that when he loaded it with 50 Ohms, it went back to a
sinewave.   Maybe that non-linearity went away when it was loaded ?
Could be some kind of termination non-linearity or even coming from
the source with the higher levels of reflections.  Can't explain it
otherwise.

boB