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 11:48:32 +0000 From: Joe Gwinn Newsgroups: sci.electronics.design Subject: Re: Distorted Sine Wave Date: Mon, 03 Jun 2024 07:48:32 -0400 Message-ID: <24br5jpsiiraulfsb8sd3mv3fdhv6ag6nn@4ax.com> 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: 155 X-Usenet-Provider: http://www.giganews.com X-Trace: sv3-8X6yczWS4dtyZ+xeTTAkH27yn3QLPlUpnNJTuiFf2/pZR/31CaMh4HFj+EvEoQN4PFdwN5kpEGv7RWU!Knw8nFRa8AFx7Z/vEpZAV5vCVknmGlCtwJXGQHTRSZMUwSKXZppAruKHtetWVDacz+FgHik= 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: 8076 On Sun, 2 Jun 2024 20:58:45 -0000 (UTC), Cursitor Doom wrote: >On Sun, 02 Jun 2024 14:08:48 -0400, Joe Gwinn wrote: > >> On Sun, 2 Jun 2024 16:55:28 -0000 (UTC), Cursitor Doom >> wrote: >> >>>On Sun, 02 Jun 2024 12:19:05 -0400, 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! >>>>>>>>>>> >>>>>>>>>>> >>>>>>>>>> And >>>>>>>>>> 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: >>>> >>>> .>>B07MP9D9GC?th=1> >>>> >>>> Just buying a few of these and doing some experiments will be far >>>> cheaper and faster than the various alternatives discussed.t >>>> >>>> Joe Gwinn >>> >>>I think you're looking at the first picture with the signal into the >>>scope's 1 Meg input. The 50 ohm trace is only 850mV peak-to-peak or >>>thereabouts and when I measured it with an actual power meter, came out >>>at about +2.5dBm so within the range you stated; no attenuation needed >>>(thanks for the range, by the way; I needed to know that). >> >> What we don't know is exactly how you made the various measurements. If >> you are observing the signal from the 10 MHz reference where it enters >> the analyzer, I would expect that there is a T-connector with the scope >> (set to 1 Mohm) listening in to passing signals. > >You did ask me this before and did post an answer. See Message-ID: > > >You also still appear to think that the 10Mhz signal is going into the >analyzer. It isn't. It's coming out. Again, see Message-ID: > I did read that, but didn't know what to make of it. I think an annotated drawing is required. On this drawing, where do the various scope traces mentioned up-thread come from? Joe Gwinn >> In this case, the load seen by the incoming reference is that provided >> by the input on the analyzer. Which input is +10 dBm max. If you set >> the observing scope input to 50 ohm, the reference will see a 25 ohm >> load, cutting the signal seen by the analyzer by 3 dB. Which will take >> +13 dBm down to +10 dBm, which is in range. >> >> A 3dB attenuator in line will drop the signal to 10 dBm as well. >> >> I've built lots of systems like that. The 10 MHz reference is delivered >> to everybody at +13 dBm, and it is the receivers' responsibility to >> attenuate it to whatever they need. >> >> >>>I've now measured the 100Mhz oscillator and that seems fine, although I >>>only saw 0.61V p-p into 50 ohms, so somewhat less than the 10Mhz >>>oscillator's output. >>>So far, I've not measured anything which screams "the fault's here!" as >>>all the expected signals are present - although admittedly I have many >>>more to test. But certainly all the *major* signals within this complex >>>beast are present. It's looking like it could be an issue with one of >>>the phase detectors or LPFs. Sigh.... >> >> To my eye, it does scream. >> >> Joe Gwinn