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NNTP-Posting-Date: Thu, 30 May 2024 01:19:41 +0000
From: boB <boB@K7IQ.com>
Newsgroups: sci.electronics.design
Subject: Re: Distorted Sine Wave
Date: Wed, 29 May 2024 18:19:40 -0700
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On Wed, 29 May 2024 20:49:27 -0000 (UTC), Cursitor Doom
<cd999666@notformail.com> wrote:

>On Wed, 29 May 2024 13:42:13 -0700, john larkin wrote:
>
>> 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
>>>
>>>
>>>Looks like reflections in the cable. Try the 50 Ohm termination.
>>>
>>>Arie
>> 
>> If the drive is a sine wave, a cable can't generate that 2nd harmonic.
>
>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. :)
>
>
>> Our boxes output a 10 MHz square wave. Our clock inputs have a 10 MHz
>> bandpass filter, so they accept most anything.

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).

Learned something here though.

boB
AZ