Path: ...!Xl.tags.giganews.com!local-2.nntp.ord.giganews.com!nntp.supernews.com!news.supernews.com.POSTED!not-for-mail NNTP-Posting-Date: Thu, 30 May 2024 23:24:25 +0000 From: john larkin Newsgroups: sci.electronics.design Subject: Re: Distorted Sine Wave Date: Thu, 30 May 2024 16:24:25 -0700 Message-ID: <9k2i5jpfhu3ncfpm28ukusrok4hugal80s@4ax.com> References: <3lcf5jd7li0a3c0fgddt7o8lnfocvls2pr@4ax.com> <48bd78e1-7da8-3bba-2879-d22962203fa3@electrooptical.net> <9olh5j9al34fhrebr4grqq8h6c8javjpp1@4ax.com> <1n0i5jh257hiinlj2dhaatlo11s33m5n0e@4ax.com> User-Agent: ForteAgent/8.00.32.1272 MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8bit Lines: 80 X-Trace: sv3-AjKzcnDJmzeKiIc+6+W4gl5udxwm3m1rISZZd+EPjIqj3Xug+rnCTwhja96sX0qLidxBi91CJMDsU5J!WTsUfkWxkE2MAke+7ad97o7aM7LFdB38RS1I9EYe8dtmZyRohhkrEro7Q52QU5xpKgDlPVwqLufL!x2YfHA== 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: 4741 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.