Path: ...!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail
From: Cursitor Doom <cd999666@notformail.com>
Newsgroups: sci.electronics.design
Subject: Re: Distorted Sine Wave
Date: Wed, 29 May 2024 21:54:32 -0000 (UTC)
Organization: A noiseless patient Spider
Lines: 49
Message-ID: <v3886o$1aj2a$1@dont-email.me>
References: <v37ncd$17q1d$1@dont-email.me>
	<nnd$1540c445$35e5ece6@6a11785c39b8fb50>
	<vi4f5jlua68idhefpgddthl2q08luvtqqg@4ax.com> <v384cn$1a1og$1@dont-email.me>
	<v385h4$19vg4$1@dont-email.me>
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
Injection-Date: Wed, 29 May 2024 23:54:32 +0200 (CEST)
Injection-Info: dont-email.me; posting-host="3e46153d5b3066d07fa4107a672bc40d";
	logging-data="1395786"; mail-complaints-to="abuse@eternal-september.org";	posting-account="U2FsdGVkX18foSm/GsIl7h7g/jMVjO7qkJPggSOwghQ="
User-Agent: Pan/0.149 (Bellevue; 4c157ba)
Cancel-Lock: sha1:RWBgS/MgOHxXLPuF7U4EOAMZNx0=
Bytes: 2957

On Wed, 29 May 2024 23:10:56 +0200, Jeroen Belleman wrote:

> On 5/29/24 22:49, Cursitor Doom 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. :)
> 
> If this oscillator is made to drive 50 Ohms and you don't provide that,
> internal buffer stages may saturate or do other weird things. If it
> works OK *with* the 50 Ohm load, then your problem is solved, no?
> 
> Jeroen Belleman

Unfortunately not. the suspicion that there was something wrong with that 
oscillator was my main hope of an easy fix for this analyzer. Now I have 
to go back to the drawing board and start trouble-shooting all over again. 
And it's a complex beast!