Path: ...!Xl.tags.giganews.com!local-2.nntp.ord.giganews.com!news.giganews.com.POSTED!not-for-mail NNTP-Posting-Date: Thu, 30 May 2024 22:53:30 +0000 From: Joe Gwinn Newsgroups: sci.electronics.design Subject: Re: Distorted Sine Wave Date: Thu, 30 May 2024 18:53:29 -0400 Message-ID: <1n0i5jh257hiinlj2dhaatlo11s33m5n0e@4ax.com> References: <3lcf5jd7li0a3c0fgddt7o8lnfocvls2pr@4ax.com> <48bd78e1-7da8-3bba-2879-d22962203fa3@electrooptical.net> <9olh5j9al34fhrebr4grqq8h6c8javjpp1@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: 74 X-Usenet-Provider: http://www.giganews.com X-Trace: sv3-HuL2j17Q17Gba5CJJFay1CcD60hc0xs1PQQ5LQmaW8GcNztXTvgm7uXoCwsSi3DqZDlpve7AHqHUaxC!KfeMx14MaiExLhs2Qqk3gj+kYK3vXixO4E7XXqOVbSjCi1YOYHJ2rIYQa/n2A3hnXdtNtMk= 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: 4509 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