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: Mon, 3 Jun 2024 19:38:21 +0200 Organization: A noiseless patient Spider Lines: 172 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; format=flowed Content-Transfer-Encoding: 7bit Injection-Date: Mon, 03 Jun 2024 19:36:17 +0200 (CEST) Injection-Info: dont-email.me; posting-host="56924a58ec05790d3cbdea059897404d"; logging-data="3276"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX1/LCQbLeoRrRlfrPqXpZJzm" User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.13.0 Cancel-Lock: sha1:xpCwJ0nZ7HqkichYw3Lt5txnLyI= Content-Language: en-US In-Reply-To: Bytes: 9153 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 output should deliver +5dBm into 50 Ohms. It's a bit low, then, but I doubt that this is your problem. ========== REMAINDER OF ARTICLE TRUNCATED ==========