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 03:08:58 +0000 From: john larkin Newsgroups: sci.electronics.design Subject: Re: Distorted Sine Wave Date: Wed, 29 May 2024 20:08:58 -0700 Message-ID: References: User-Agent: ForteAgent/8.00.32.1272 MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Lines: 57 X-Trace: sv3-ESxo2GZHTU7epqnmusm15Y4tQNr82zxffolZIFp6TuEt2ciTfyaM5stL9XcDk3q7aFXxsBI8Q2AXWi4!T4CWcQc23TIT8URWE4zGv1JZcHGaWMr34tasAZ+nLceGlmY+BIg2TeWOzjm7WYM4/6R0CS3hyjvl!MuvUCQ== 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: 3206 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.