Path: ...!Xl.tags.giganews.com!local-2.nntp.ord.giganews.com!news.giganews.com.POSTED!not-for-mail NNTP-Posting-Date: Mon, 03 Jun 2024 11:43:41 +0000 From: Joe Gwinn Newsgroups: sci.electronics.design Subject: Re: Distorted Sine Wave Date: Mon, 03 Jun 2024 07:43:41 -0400 Message-ID: References: <9tok5j9p388ookujrtbsofskjlbekfuhjb@4ax.com> <60rk5jti9l5154hqaqicohmj3u1lfd16g3@4ax.com> <4k6p5jhgmrigja3o0tdur5tvkfc7bsrd15@4ax.com> User-Agent: ForteAgent/8.00.32.1272 MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Lines: 118 X-Usenet-Provider: http://www.giganews.com X-Trace: sv3-yrMw3C5Kz1s08mHBOqbxes7zp3Dj++Blxql+z9nVeicZpLCGOBCM7ybiBnIoN9vppRjInM2pKe8KiOG!VNnum34HE3EZ7ljsxEozqEWm8Qln1WZEDGHE30n1E2UIj8CEja/tOpv+zCIkYhjD/iZM+V8= X-Complaints-To: abuse@giganews.com X-DMCA-Notifications: http://www.giganews.com/info/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: 6588 On Sun, 2 Jun 2024 23:45:43 +0200, Jeroen Belleman wrote: >On 6/2/24 21:44, Joe Gwinn wrote: >> On Sun, 2 Jun 2024 20:18:50 +0200, Jeroen Belleman >> wrote: >> >>> On 6/2/24 18:19, Joe Gwinn wrote: >>>> On Sun, 2 Jun 2024 11:31:33 -0000 (UTC), Cursitor Doom >>>> wrote: >>>> >>>>> On Sun, 2 Jun 2024 11:17:58 -0000 (UTC), piglet wrote: >>>>> >>>>>> Cursitor Doom wrote: >>>>>>> On Sat, 1 Jun 2024 22:00:58 -0000 (UTC), piglet wrote: >>>>>>> >>>>>>>> Cursitor Doom wrote: >>>>>>>>> On Sat, 1 Jun 2024 15:44:17 +0200, Jeroen Belleman wrote: >>>>>>>>> >>>>>>>>>> On 6/1/24 14:07, Cursitor Doom wrote: >>>>>>>>> >>>>>>>>>>> I've taken a shot of the waveform into the 50 ohm input. It's >>>>>>>>>>> around 850mV peak-peak. Hopefully the slight distortion I spoke >>>>>>>>>>> about is visible; the slightly more leisurely negative-going >>>>>>>>>>> excursions WRT their positive-going counterparts. So it's not a >>>>>>>>>>> pure sine wave as one would expect. Does it matter? I don't know! >>>>>>>>>>> >>>>>>>>>>> https://disk.yandex.com/i/7cuuBimDbOIBZw >>>>>>>>>> >>>>>>>>>> The shape looks perfectly acceptable to me. This is +3dBm into 50 >>>>>>>>>> Ohms. >>>>>>>>>> Is that what it's supposed to be? Canned reference oscillators most >>>>>>>>>> often deliver +13dBm, sometimes +10dBm. >>>>>>>>> >>>>>>>>> Is it? I only make it about half your figure: +1.65dBm. >>>>>>>>> I admit I'm frequently prone to careless errors, so stand to be >>>>>>>>> corrected, >>>>>>>>> but here's my method: >>>>>>>>> 850mV peak to peak is 425mV peak voltage. Average of that is >>>>>>>>> 0.425x0.636 = >>>>>>>>> 0.27V. Average power is average volts squared divided by the load >>>>>>>>> impedance of 50 ohms = 1.46mW = +1.65dBm. >>>>>>>>> >>>>>>>>> I shall consult the manual to see what it ought to be - if I can find >>>>>>>>> it, that is, as PDF manuals are a nightmare to navigate IME. >>>>>>>>> >>>>>>>>> >>>>>>>>> >>>>>>>> Use 0.71 for RMS instead of 0.636 ! I make that about 1.8mW or +2.6dBm >>>>>>>> ? >>>>>>> >>>>>>> Thanks, Erich. But there's no such thing as "RMS power" strictly >>>>>>> speaking IIRC, so that's why I took the average figure; not that it >>>>>>> makes much difference in practice. it does seem a bit on the low side, >>>>>>> but despite reading through the most likely sources (the service manual >>>>>>> and the trouble-shooting/repair manual) I can find nothing stated for >>>>>>> what that signal level should be! This may be due to the >>>>>>> user-unfriendliness of very large PDF manuals; I just don't know. >>>>>>> Anyway, not very satisfactory! Later today I plan to do a direct power >>>>>>> meter measurement of the ref osc (since none of us here seem to agree >>>>>>> on what 850mV vs 50 ohms equates to!!) >>>>>>> >>>>>>> >>>>>>> >>>>>>> >>>>>>> >>>>>> Since you have a power meter, a signal source, and an oscilloscope why >>>>>> not measure the peak to peak voltage on the scope and power on the power >>>>>> meter and see which calculation 0.636 vs 0.707 gives the closest >>>>>> agreement? >>>>> >>>>> It wouldn't prove anything one way or ther other, though, since that power >>>>> meter hasn't been calibrated for "quite a while" so to speak. :) >>>>> It'll give a 'good enough' reading for my purposes, but won't be accurate >>>>> enough to meaningfully test your otherwise fine suggestion. >>>> >>>> >>>> The 0 to +10 dBm range I mentioned came from the service manual. >>>> >>>> Looking at your scope picture, it looks like a 3 Vpp signal, which is >>>> +13 dBm, a very common distribution level, but one that exceeds the >>>> analyzer's allowed range. All that's needed to fix this is a 3dB >>>> inline attenuator. Here is one for SMA connectors: >>>> >>>> . >>>> >>>> Just buying a few of these and doing some experiments will be far >>>> cheaper and faster than the various alternatives discussed. >>>> >>>> Joe Gwinn >>> >>> What scope picture are you looking at? I see only 0.88Vpp. >> >> This one, posted by CD on 1 June '24: >> >> .< https://disk.yandex.com/i/7cuuBimDbOIBZw> >> >> This is the one with the funny stuff at the bottom. If you look at >> the upper waveshape, the peak amplitude to the inflection point near >> the bottom is about 1.5 Vp, which implies 3 Vpp, which is +13 dBm into >> 50 ohms. Why the inflection point? Because in a undistorted sine >> wave, the zero crossing is linear, and does not flair. The scope >> picture does not show where zero volts is, so had to use the >> inflection point. >> >> Joe Gwinn > >I'm afraid you have lost me there... I see only a roughly >sine-shaped wave framed with cursors along the peaks being >0.88V apart. I don't care about the DC level, only the 10MHz >component matters. Its amplitude is only 0.44V. I copied the wrong yandex. Try this (29 May 2024): .. Joe Gwinn