Path: ...!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail From: Phil Hobbs Newsgroups: sci.electronics.design Subject: Re: Distorted Sine Wave Date: Thu, 30 May 2024 15:02:44 -0400 Organization: A noiseless patient Spider Lines: 62 Message-ID: <48bd78e1-7da8-3bba-2879-d22962203fa3@electrooptical.net> References: <3lcf5jd7li0a3c0fgddt7o8lnfocvls2pr@4ax.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Injection-Date: Thu, 30 May 2024 21:02:46 +0200 (CEST) Injection-Info: dont-email.me; posting-host="97dd50364f95b78ab508b343dd52e7bb"; logging-data="1917496"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX19mLjRXj5CgAWzqaEPe03dQ" User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.0 Cancel-Lock: sha1:JacdyFlsMGH9gHuUrrOydiGDYZQ= In-Reply-To: <3lcf5jd7li0a3c0fgddt7o8lnfocvls2pr@4ax.com> Bytes: 3513 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. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com