Path: ...!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail From: Cursitor Doom Newsgroups: sci.electronics.design Subject: Re: Distorted Sine Wave Date: Wed, 29 May 2024 21:54:32 -0000 (UTC) Organization: A noiseless patient Spider Lines: 49 Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Injection-Date: Wed, 29 May 2024 23:54:32 +0200 (CEST) Injection-Info: dont-email.me; posting-host="3e46153d5b3066d07fa4107a672bc40d"; logging-data="1395786"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX18foSm/GsIl7h7g/jMVjO7qkJPggSOwghQ=" User-Agent: Pan/0.149 (Bellevue; 4c157ba) Cancel-Lock: sha1:RWBgS/MgOHxXLPuF7U4EOAMZNx0= Bytes: 2957 On Wed, 29 May 2024 23:10:56 +0200, Jeroen Belleman wrote: > On 5/29/24 22:49, 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. :) > > If this oscillator is made to drive 50 Ohms and you don't provide that, > internal buffer stages may saturate or do other weird things. If it > works OK *with* the 50 Ohm load, then your problem is solved, no? > > Jeroen Belleman Unfortunately not. the suspicion that there was something wrong with that oscillator was my main hope of an easy fix for this analyzer. Now I have to go back to the drawing board and start trouble-shooting all over again. And it's a complex beast!