Path: ...!weretis.net!feeder8.news.weretis.net!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail From: Jeroen Belleman Newsgroups: sci.electronics.design Subject: Re: Distorted Sine Wave Date: Sat, 1 Jun 2024 15:44:17 +0200 Organization: A noiseless patient Spider Lines: 184 Message-ID: References: <3lcf5jd7li0a3c0fgddt7o8lnfocvls2pr@4ax.com> <48bd78e1-7da8-3bba-2879-d22962203fa3@electrooptical.net> <9olh5j9al34fhrebr4grqq8h6c8javjpp1@4ax.com> <1n0i5jh257hiinlj2dhaatlo11s33m5n0e@4ax.com> <9k2i5jpfhu3ncfpm28ukusrok4hugal80s@4ax.com> <9tok5j9p388ookujrtbsofskjlbekfuhjb@4ax.com> <60rk5jti9l5154hqaqicohmj3u1lfd16g3@4ax.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Injection-Date: Sat, 01 Jun 2024 15:42:14 +0200 (CEST) Injection-Info: dont-email.me; posting-host="b468be62246aee18e699b2c151c2dd5b"; logging-data="2955526"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX18jKkNG4I9B2SSlMr9OdFZU" User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.13.0 Cancel-Lock: sha1:uSodXq866X28itw08UYw0qQgx8U= In-Reply-To: Content-Language: en-US Bytes: 9159 On 6/1/24 14:07, Cursitor Doom wrote: > On Fri, 31 May 2024 17:33:51 -0700, boB wrote: > >> On Fri, 31 May 2024 17:02:13 -0700, boB wrote: >> >>> On Fri, 31 May 2024 21:40:04 -0000 (UTC), Cursitor Doom >>> wrote: >>> >>>> On Fri, 31 May 2024 15:10:32 -0400, Joe Gwinn wrote: >>>> >>>>> On Fri, 31 May 2024 18:54:06 -0000 (UTC), Cursitor Doom >>>>> wrote: >>>>> >>>>>> On Fri, 31 May 2024 11:34:46 -0400, Joe Gwinn wrote: >>>>>> >>>>>>> On Thu, 30 May 2024 16:24:25 -0700, john larkin >>>>>>> wrote: >>>>>>> >>>>>>>> On Thu, 30 May 2024 18:53:29 -0400, Joe Gwinn >>>>>>>> >>>>>>>> wrote: >>>>>>>> >>>>>>>>> On Thu, 30 May 2024 14:56:30 -0700, john larkin >>>>>>>>> wrote: >>>>>>>>> >>>>>>>>>> On Thu, 30 May 2024 16:06:47 -0400, Joe Gwinn >>>>>>>>>> >>>>>>>>>> wrote: >>>>>>>>>> >>>>>>>>>>> On Thu, 30 May 2024 15:02:44 -0400, Phil Hobbs >>>>>>>>>>> wrote: >>>>>>>>>>> >>>>>>>>>>>> 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. >>>>>>>>>>> >>>>>>>>>>> Plus some LC filter wiggles, to distort and smooth things. >>>>>>>>>>> >>>>>>>>>>> I dug around and found a copy of the HP 8566B spectrum analyzer >>>>>>>>>>> service manual. The 10 MHz ref input is an amplifier driving a >>>>>>>>>>> mixer, >>>>>>>>>>> with not hint of for instance a TTL input. So, the problem must >>>>>>>>>>> be elsewhere. Or, it's just busted. >>>>>>>>>>> >>>>>>>>>>> .>>>>> xdevs.com/doc/HP_Agilent_Keysight/ >>>>>> HP%208566B%20Troubleshooting%20&%20Repair%20Vol.%201.pdf> >>>>>>>>>>> >>>>>>>>>>> Joe Gwinn >>>>>>>>>> >>>>>>>>>> 334 pages! Where is the issue? >>>>>>>>> >>>>>>>>> The pagination was unclear, so I didn't see a way to say. How I >>>>>>>>> found it was to look at the schematics. Look for module A22. >>>>>>>>> Don't think search works on such images, but visual search didn't >>>>>>>>> take that long. >>>>>>>>> >>>>>>>>> Joe Gwinn >>>>>>>> >>>>>>>> Too much work for free consulting. >>>>>>> >>>>>>> I took another look. There is a page reference on the right edge, >>>>>>> near the bottom, which is not marked as a page X of Y, but is. >>>>>>> >>>>>>> Anyway, look at pages 59 and 77. At 77, look for A22 in the lower >>>>>>> left region. Just above, look for INT and EXT jacks. The EXT jack >>>>>>> is where an external reference enters. >>>>>>> >>>>>>> Joe Gwinn >>>>>> >>>>>> It's just a block diagram of the reference oscillator module. There's >>>>>> no detailed schematic of the oscillator itself. At least that's the >>>>>> case with the PDF version of the Service Manual I have. >>>>> >>>>> It's probably in the book that I don't have, if it was ever released. >>>>> >>>>> Joe Gwinn >>>> >>>> HP actually published at least 5 manuals of various kinds about this >>>> analyzer, so it's possible it's in one of the others. However, the >>>> actual service manual is where I'd expect to find it if they published >>>> it at all. >>>> The other titles are: >>>> >>>> HP 8566B Operator's Manual HP 8566B Installation and Verification >>>> Manual HP 8566B Test and Adjustments Manual HP 8566B Troubleshooting >>>> and Repair Manual >>>> >>>> So if the answers are not in *any* of the above, it'd be jolly rotten >>>> luck indeed! >>> >>> >>> >>> Looking at that waveform again... >>> >>> Could it be that the wavform you are seeing there is not a harmonic but >>> just a partial cancelation due to reflections ? >>> >>> If you look at one peak vs. the other, they look about the same time to >>> me. About 1 scope division. Just the amplitude looks different on >>> alternating cycles. A non-linearity I would think would make an even >>> harmonic. >> >> I thought I said the wrong thing ! I mean odd harmonic(s) from a >> non-linearity. >> >> >>> 2nd harmonic is usually due to non 1/2 wave symetry (DC >>> offset bascially) >>> >>> >> Here, I meant even harmonic(s) not just second harmonic. >> >> It's rather hot today in Phoenix.. > > 1. Everybody makes careless mistakes. ========== REMAINDER OF ARTICLE TRUNCATED ==========