Path: ...!Xl.tags.giganews.com!local-2.nntp.ord.giganews.com!nntp.supernews.com!news.supernews.com.POSTED!not-for-mail NNTP-Posting-Date: Sat, 01 Jun 2024 00:02:15 +0000 From: boB Newsgroups: sci.electronics.design Subject: Re: Distorted Sine Wave Date: Fri, 31 May 2024 17:02:13 -0700 Message-ID: <9tok5j9p388ookujrtbsofskjlbekfuhjb@4ax.com> References: <3lcf5jd7li0a3c0fgddt7o8lnfocvls2pr@4ax.com> <48bd78e1-7da8-3bba-2879-d22962203fa3@electrooptical.net> <9olh5j9al34fhrebr4grqq8h6c8javjpp1@4ax.com> <1n0i5jh257hiinlj2dhaatlo11s33m5n0e@4ax.com> <9k2i5jpfhu3ncfpm28ukusrok4hugal80s@4ax.com> User-Agent: ForteAgent/8.00.32.1272 MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Lines: 153 X-Trace: sv3-JuSuMuFncdlCFu4UyHNbeZHj0LyKV+vg+fa2gPd2tA/6n8DAiGx9jx3SheE1YImINtRTf93HHHvHham!HgtGOknKY7zA2bHMtjglY0uP4pcMOTu8zNdnMYC6BaZs2e4PC+YKPvKXzD7FQfHWBOn/R2jnk6m8!3fhv9YCD X-Complaints-To: www.supernews.com/docs/abuse.html X-DMCA-Complaints-To: www.supernews.com/docs/dmca.html X-Abuse-and-DMCA-Info: Please be sure to forward a copy of ALL headers X-Abuse-and-DMCA-Info: Otherwise we will be unable to process your complaint properly X-Postfilter: 1.3.40 Bytes: 7505 On Fri, 31 May 2024 21:40:04 -0000 (UTC), Cursitor Doom wrote: >On Fri, 31 May 2024 15:10:32 -0400, Joe Gwinn wrote: > >> On Fri, 31 May 2024 18:54:06 -0000 (UTC), Cursitor Doom >> wrote: >> >>>On Fri, 31 May 2024 11:34:46 -0400, Joe Gwinn wrote: >>> >>>> On Thu, 30 May 2024 16:24:25 -0700, john larkin wrote: >>>> >>>>>On Thu, 30 May 2024 18:53:29 -0400, Joe Gwinn >>>>>wrote: >>>>> >>>>>>On Thu, 30 May 2024 14:56:30 -0700, john larkin >>>>>>wrote: >>>>>> >>>>>>>On Thu, 30 May 2024 16:06:47 -0400, Joe Gwinn >>>>>>>wrote: >>>>>>> >>>>>>>>On Thu, 30 May 2024 15:02:44 -0400, Phil Hobbs >>>>>>>> wrote: >>>>>>>> >>>>>>>>>On 2024-05-29 18:59, Joe Gwinn wrote: >>>>>>>>>> On Wed, 29 May 2024 22:11:47 -0000 (UTC), Phil Hobbs >>>>>>>>>> wrote: >>>>>>>>>> >>>>>>>>>>> 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 >>>>>>>>>>>>> >>>>>>>>>>>>> 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. >>>>>>>> >>>>>>>>.>>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! Looking at that waveform again... Could it be that the wavform you are seeing there is not a harmonic but just a partial cancelation due to reflections ? If you look at one peak vs. the other, they look about the same time to me. About 1 scope division. Just the amplitude looks different on alternating cycles. A non-linearity I would think would make an even harmonic. 2nd harmonic is usually due to non 1/2 wave symetry (DC offset bascially) What was tha amplitude after you loaded it down properly ? How about a picture ? Where were you scoping this at again ? boB