Path: ...!local-4.nntp.ord.giganews.com!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 01:19:41 +0000 From: boB Newsgroups: sci.electronics.design Subject: Re: Distorted Sine Wave Date: Wed, 29 May 2024 18:19:40 -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: 45 X-Trace: sv3-osjgpgC2ix3B6GOhLBtg3/JZ6iKpFTfFxf/Q82dPnYqpvn+lRVrghY6DEcdxiaBWKw647dCgmPeHOA+!KzwIS3UP7IOWdQMbTlermvjopP/czf6jDugibD5K+R7FMEF1sBxz6QkzwBs85V9NfAbTNoCqCko2!vf6Yxs7V 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: 2789 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