Path: ...!weretis.net!feeder8.news.weretis.net!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: Mon, 3 Jun 2024 17:53:50 -0000 (UTC) Organization: A noiseless patient Spider Lines: 186 Message-ID: References: <9tok5j9p388ookujrtbsofskjlbekfuhjb@4ax.com> <60rk5jti9l5154hqaqicohmj3u1lfd16g3@4ax.com> <4k6p5jhgmrigja3o0tdur5tvkfc7bsrd15@4ax.com> <24br5jpsiiraulfsb8sd3mv3fdhv6ag6nn@4ax.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Injection-Date: Mon, 03 Jun 2024 19:53:50 +0200 (CEST) Injection-Info: dont-email.me; posting-host="41aefe14710384ba0e8c1da4542c03bc"; logging-data="8537"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX1+9NgADYOeT0b4KpO0WNevNUuJ1jnSLRyY=" User-Agent: Pan/0.149 (Bellevue; 4c157ba) Cancel-Lock: sha1:221dl1MJW+LW54zZ+Ck2v9qL3Ks= Bytes: 9796 On Mon, 3 Jun 2024 19:38:21 +0200, Jeroen Belleman wrote: > On 6/3/24 17:43, Cursitor Doom wrote: >> On Mon, 03 Jun 2024 07:48:32 -0400, Joe Gwinn wrote: >> >>> 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 >> >> Joe, I appreciate you're only trying to help, but don't worry about it. >> I don't believe the oscillator this thread relates to is causing the >> PLL unlock error so we've all gone down a bit of a rabbit hole with >> this one. >> I really need to look elsewhere for the culprit. > > For what it's worth, I found a manual on the web saying that the 10MHz ========== REMAINDER OF ARTICLE TRUNCATED ==========