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From: Cursitor Doom <cd999666@notformail.com>
Newsgroups: sci.electronics.design
Subject: Re: Distorted Sine Wave
Date: Mon, 3 Jun 2024 17:53:50 -0000 (UTC)
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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
>>> <cd999666@notformail.com> 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
>>>>> <cd999666@notformail.com> 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
>>>>>>> <cd999666@notformail.com> wrote:
>>>>>>>
>>>>>>>> On Sun, 2 Jun 2024 11:17:58 -0000 (UTC), piglet wrote:
>>>>>>>>
>>>>>>>>> Cursitor Doom <cd999666@notformail.com> wrote:
>>>>>>>>>> On Sat, 1 Jun 2024 22:00:58 -0000 (UTC), piglet wrote:
>>>>>>>>>>
>>>>>>>>>>> Cursitor Doom <cd999666@notformail.com> 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>
>>>>>>>>>>>>>
>>>>>>>>>>>>>
>>> And <https://disk.yandex.com/i/z6fYbeVfPRK7aA>
>>>
>>>
>>>>>>>>>>>>> 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:
>>>>>>>
>>>>>>> .<https://www.amazon.com/MWRF-Source-Male-Female-Attenuator/dp/
>>>>>> 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:
>>>> <v3fsbp$2u0a6$1@dont-email.me>
>>>>
>>>> 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:
>>>> <v3fsbp$2u0a6$1@dont-email.me>
>>>
>>> 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
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