Path: ...!news.mixmin.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 18:54:06 -0000 (UTC) Organization: A noiseless patient Spider Lines: 105 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: Fri, 31 May 2024 20:54:07 +0200 (CEST) Injection-Info: dont-email.me; posting-host="5298e01e4585ab4377a4cf319f61075c"; logging-data="2448975"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX1/kiI7zIF12F/7d7C1f3xKklk/tf11INiM=" User-Agent: Pan/0.149 (Bellevue; 4c157ba) Cancel-Lock: sha1:8eOvlKS1zrD/z1UYSPtGQHLdlkU= Bytes: 5698 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. >>>>> >>>>>. >>>>> >>>>>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.