Path: ...!local-1.nntp.ord.giganews.com!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 18:55:55 +0000 From: boB Newsgroups: sci.electronics.design Subject: Re: Distorted Sine Wave Date: Thu, 30 May 2024 11:55:55 -0700 Message-ID: <7mih5jhqoqvrrlhuo7capibe2cetggqcce@4ax.com> References: User-Agent: ForteAgent/8.00.32.1272 MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Lines: 69 X-Trace: sv3-UxaSu8OM5xkANkA8Uw/aIyI1H/kjFsAUy+mf+j1C4HiatnLnt+/u3QhOJewIBVSclq5c7A+aZwfFD9p!ycEw9fB9DeyiqTT/oAqN1DsIbswPiJlB/7aHMdOF+lz3klxJVcBIa6KG3ivOhPjlKKXs0UoqhmGu!QZunbyQI 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: 3718 On Wed, 29 May 2024 20:08:58 -0700, john larkin wrote: >On Wed, 29 May 2024 18:19:40 -0700, boB wrote: > >>On Wed, 29 May 2024 20:49:27 -0000 (UTC), 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. :) >>> >>> >>>> Our boxes output a 10 MHz square wave. Our clock inputs have a 10 MHz >>>> bandpass filter, so they accept most anything. >> >>Weird but I'm not surprised that 4 feet if coax, unloaded at 10 MHz >>gives a strange waveform. Can simulate this, I believe, in LTspice >>using the transmission line element(s). >> >>Learned something here though. >> >>boB >>AZ > >No txline can create frequency components that are not in the source. > >(Well, a NLTL can, but 4 feet of coax isn't a shock line.) > >But the problem, as usual, is underspecified. Maybe some driver is >going nonlinear. A schematic would help. > > I was thinking the same thing. Non-linearity. But he said that when he loaded it with 50 Ohms, it went back to a sinewave. Maybe that non-linearity went away when it was loaded ? Could be some kind of termination non-linearity or even coming from the source with the higher levels of reflections. Can't explain it otherwise. boB