Path: ...!npeer.as286.net!npeer-ng0.as286.net!3.eu.feeder.erje.net!feeder.erje.net!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail From: Cursitor Doom Newsgroups: sci.electronics.design Subject: Re: Distorted Sine Wave Date: Fri, 31 May 2024 22:17:37 -0000 (UTC) Organization: A noiseless patient Spider Lines: 129 Message-ID: References: <3lcf5jd7li0a3c0fgddt7o8lnfocvls2pr@4ax.com> <48bd78e1-7da8-3bba-2879-d22962203fa3@electrooptical.net> <9olh5j9al34fhrebr4grqq8h6c8javjpp1@4ax.com> <1n0i5jh257hiinlj2dhaatlo11s33m5n0e@4ax.com> <9k2i5jpfhu3ncfpm28ukusrok4hugal80s@4ax.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Injection-Date: Sat, 01 Jun 2024 00:17:37 +0200 (CEST) Injection-Info: dont-email.me; posting-host="722a1db93b34a23f770c1bceecb5bb8e"; logging-data="2448975"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX198e15B+1rzQBCKDNN9xL/TNBitcxgXN4M=" User-Agent: Pan/0.149 (Bellevue; 4c157ba) Cancel-Lock: sha1:VXdtXXf4Bba2238ElP2ZzsIN/3U= Bytes: 6828 On Fri, 31 May 2024 14:48:28 -0400, Joe Gwinn wrote: > On Fri, 31 May 2024 17:29:47 -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 >> >>I don't believe the 10Mhz ref osc is the problem, John. The 2nd harmonic >>distortion goes away when the scope input impedance is set to 50 ohms. >>There is some slight distortion on it, but not enough to cause an >>out-of- lock error. Furthermore, since that osc is the pace-setter for >>every other module in every other loop in this analyzer, its failure >>would give rise to way more error messages than a mere "YTO unlock" as >>it stands at present. The manual suggests the most likely areas where >>the fault is located are in one of the boards A19, A20, A21 or A11. If >>A22 were the culprit, there would be over a dozen error messages. > > What is the 10 MHz signal power level at the EXT input in these two > castes, 1 Mohm and 50 Ohm? The expected range is 0 to +10 dBm. > > Joe Gwinn 7.68dBm on 50 Ohms 2.68V P-P on 1 Meg No issues there AFAIC.