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From: Joe Gwinn <joegwinn@comcast.net>
Newsgroups: sci.electronics.design
Subject: Re: Distorted Sine Wave
Date: Fri, 31 May 2024 15:10:32 -0400
Message-ID: <m38k5jlbqo39gr9223b0vg93e8lrbrpurr@4ax.com>
References: <vi4f5jlua68idhefpgddthl2q08luvtqqg@4ax.com> <v384cn$1a1og$1@dont-email.me> <v38973$1atf2$1@dont-email.me> <3lcf5jd7li0a3c0fgddt7o8lnfocvls2pr@4ax.com> <48bd78e1-7da8-3bba-2879-d22962203fa3@electrooptical.net> <9olh5j9al34fhrebr4grqq8h6c8javjpp1@4ax.com> <seth5jlmgu2gv6lr61m31jk2q94073rvtk@4ax.com> <1n0i5jh257hiinlj2dhaatlo11s33m5n0e@4ax.com> <9k2i5jpfhu3ncfpm28ukusrok4hugal80s@4ax.com> <c6rj5j1l1gfoskul3nnvudf3nc57017k84@4ax.com> <v3d6ce$2anif$2@dont-email.me>
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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