Path: ...!Xl.tags.giganews.com!local-1.nntp.ord.giganews.com!nntp.supernews.com!news.supernews.com.POSTED!not-for-mail NNTP-Posting-Date: Thu, 30 May 2024 21:56:30 +0000 From: john larkin Newsgroups: sci.electronics.design Subject: Re: Distorted Sine Wave Date: Thu, 30 May 2024 14:56:30 -0700 Message-ID: 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: 67 X-Trace: sv3-q0tvYxTcLveS4ZB9i7Sj8tM4yiIGQgV+n5UFYn4RDdQYWZqORr0h4ZW5Krz+SOLweoM2XMshnD1W7IN!PCPjPrYg+az064l5xZcUxMRPNd/fAwaM8ZeQjhdclKBaHi1GLU4b4LGlKttnwYt1JsOxlKVEwcDt!mi++6w== 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: 4091 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?