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From: Cursitor Doom <cd999666@notformail.com>
Newsgroups: sci.electronics.design
Subject: Re: Distorted Sine Wave
Date: Fri, 31 May 2024 21:40:04 -0000 (UTC)
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On Fri, 31 May 2024 15:10:32 -0400, Joe Gwinn wrote:

> On Fri, 31 May 2024 18:54:06 -0000 (UTC), Cursitor Doom
> <cd999666@notformail.com> wrote:
> 
>>On Fri, 31 May 2024 11:34:46 -0400, Joe Gwinn wrote:
>>
>>> On Thu, 30 May 2024 16:24:25 -0700, john larkin <jl@650pot.com> wrote:
>>> 
>>>>On Thu, 30 May 2024 18:53:29 -0400, Joe Gwinn <joegwinn@comcast.net>
>>>>wrote:
>>>>
>>>>>On Thu, 30 May 2024 14:56:30 -0700, john larkin <jl@650pot.com>
>>>>>wrote:
>>>>>
>>>>>>On Thu, 30 May 2024 16:06:47 -0400, Joe Gwinn <joegwinn@comcast.net>
>>>>>>wrote:
>>>>>>
>>>>>>>On Thu, 30 May 2024 15:02:44 -0400, Phil Hobbs
>>>>>>><pcdhSpamMeSenseless@electrooptical.net> wrote:
>>>>>>>
>>>>>>>>On 2024-05-29 18:59, Joe Gwinn wrote:
>>>>>>>>> On Wed, 29 May 2024 22:11:47 -0000 (UTC), Phil Hobbs
>>>>>>>>> <pcdhSpamMeSenseless@electrooptical.net> wrote:
>>>>>>>>> 
>>>>>>>>>> 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. :)
>>>>>>>>>>
>>>>>>>>>> That?s pretty diagnostic. There must be an LC filter on the
>>>>>>>>>> output?mis-terminating it will cause all sorts of
>>>>>>>>>> frequency-response whoopdedoos.
>>>>>>>>> 
>>>>>>>>> It also occurs to me that if there is a diode in series with a
>>>>>>>>> resistor somewhere, the impedance presented to the feed coax may
>>>>>>>>> be 50 ohms for positive input voltage, and say 10 Kohm for
>>>>>>>>> negative.  At the very least one could get an inverted
>>>>>>>>> reflection on negative.
>>>>>>>>> 
>>>>>>>>> Joe Gwinn
>>>>>>>>> 
>>>>>>>>Yeah, or an emitter follower.  Good point.
>>>>>>>
>>>>>>>Plus some LC filter wiggles, to distort and smooth things.
>>>>>>>
>>>>>>>I dug around and found a copy of the HP 8566B spectrum analyzer
>>>>>>>service manual.  The 10 MHz ref input is an amplifier driving a
>>>>>>>mixer,
>>>>>>>with not hint of for instance a TTL input.  So, the problem must be
>>>>>>>elsewhere.  Or, it's just busted.
>>>>>>>
>>>>>>>.<chrome-extension://efaidnbmnnnibpcajpcglclefindmkaj/https://
>>xdevs.com/doc/HP_Agilent_Keysight/
>>HP%208566B%20Troubleshooting%20&%20Repair%20Vol.%201.pdf>
>>>>>>>
>>>>>>>Joe Gwinn
>>>>>>
>>>>>>334 pages! Where is the issue?
>>>>>
>>>>>The pagination was unclear, so I didn't see a way to say.  How I
>>>>>found it was to look at the schematics.  Look for module A22.  Don't
>>>>>think search works on such images, but visual search didn't take that
>>>>>long.
>>>>>
>>>>>Joe Gwinn
>>>>
>>>>Too much work for free consulting.
>>> 
>>> I took another look.  There is a page reference on the right edge,
>>> near the bottom, which is not marked as a page X of Y, but is.
>>> 
>>> Anyway, look at pages 59 and 77.  At 77, look for A22 in the lower
>>> left region.  Just above, look for INT and EXT jacks.  The EXT jack is
>>> where an external reference enters.
>>> 
>>> Joe Gwinn
>>
>>It's just a block diagram of the reference oscillator module. There's no
>>detailed schematic of the oscillator itself. At least that's the case
>>with the PDF version of the Service Manual I have.
> 
> It's probably in the book that I don't have, if it was ever released.
> 
> Joe Gwinn

HP actually published at least 5 manuals of various kinds about this 
analyzer, so it's possible it's in one of the others. However, the actual 
service manual is where I'd expect to find it if they published it at all.
The other titles are:

HP 8566B Operator's Manual
HP 8566B Installation and Verification Manual
HP 8566B Test and Adjustments Manual
HP 8566B Troubleshooting and Repair Manual

So if the answers are not in *any* of the above, it'd be jolly rotten luck 
indeed!