Path: ...!Xl.tags.giganews.com!local-1.nntp.ord.giganews.com!news.giganews.com.POSTED!not-for-mail NNTP-Posting-Date: Fri, 31 May 2024 19:10:33 +0000 From: Joe Gwinn Newsgroups: sci.electronics.design Subject: Re: Distorted Sine Wave Date: Fri, 31 May 2024 15:10:32 -0400 Message-ID: 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: 112 X-Usenet-Provider: http://www.giganews.com X-Trace: sv3-BLVRHE3vPHKWbHlhuRwy4FSF4f9eTH+UrApUmkucL2vLhdLmYvDg9IfTR6n2p1dLpjyrGVb3jY4Z63m!LFfaQDsbcXbId3L3cMJL4vmpU3ATBaQCb1WhyL7sqwaZFAXvPZCRpYzDWYRTzKlJ1ysyFGU= X-Complaints-To: abuse@giganews.com X-DMCA-Notifications: http://www.giganews.com/info/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: 5999 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