Path: ...!feeds.phibee-telecom.net!3.eu.feeder.erje.net!feeder.erje.net!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail
From: Cursitor Doom <cd999666@notformail.com>
Newsgroups: sci.electronics.design
Subject: Re: Distorted Sine Wave
Date: Sun, 2 Jun 2024 13:53:55 -0000 (UTC)
Organization: A noiseless patient Spider
Lines: 109
Message-ID: <v3hthj$3ccih$2@dont-email.me>
References: <3lcf5jd7li0a3c0fgddt7o8lnfocvls2pr@4ax.com>
	<48bd78e1-7da8-3bba-2879-d22962203fa3@electrooptical.net>
	<9olh5j9al34fhrebr4grqq8h6c8javjpp1@4ax.com>
	<seth5jlmgu2gv6lr61m31jk2q94073rvtk@4ax.com>
	<1n0i5jh257hiinlj2dhaatlo11s33m5n0e@4ax.com>
	<9k2i5jpfhu3ncfpm28ukusrok4hugal80s@4ax.com>
	<c6rj5j1l1gfoskul3nnvudf3nc57017k84@4ax.com> <v3d6ce$2anif$2@dont-email.me>
	<m38k5jlbqo39gr9223b0vg93e8lrbrpurr@4ax.com> <v3dg3k$2anif$3@dont-email.me>
	<9tok5j9p388ookujrtbsofskjlbekfuhjb@4ax.com>
	<60rk5jti9l5154hqaqicohmj3u1lfd16g3@4ax.com> <v3f2uh$2ni6q$1@dont-email.me>
	<v3f8fl$2q686$1@dont-email.me> <v3fii8$2raur$1@dont-email.me>
	<v3g5mq$300p6$1@dont-email.me> <v3g735$3099t$1@dont-email.me>
	<v3hm40$3b87n$1@dont-email.me> <v3hnec$3bda7$1@dont-email.me>
	<v3hqbh$3bstp$1@dont-email.me>
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
Injection-Date: Sun, 02 Jun 2024 15:53:56 +0200 (CEST)
Injection-Info: dont-email.me; posting-host="40a1d383888994c45f6bff6cd4b36ba9";
	logging-data="3551825"; mail-complaints-to="abuse@eternal-september.org";	posting-account="U2FsdGVkX1+s+VJlASuZXa5ntPtX0+Ci65kZEyTPRtU="
User-Agent: Pan/0.149 (Bellevue; 4c157ba)
Cancel-Lock: sha1:MRpJgK/AOsvyAfv6J/9/kNl4qeI=
Bytes: 6274

On Sun, 2 Jun 2024 12:59:30 -0000 (UTC), Phil Hobbs wrote:

> Cursitor Doom <cd999666@notformail.com> wrote:
>> On Sun, 2 Jun 2024 13:49:16 +0200, Jeroen Belleman wrote:
>> 
>>> On 6/2/24 00:24, piglet wrote:
>>>> piglet <erichpwagner@hotmail.com> 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
>>>>>>> 
>>>>>>> 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 ?
>>>>> 
>>>>> 
>>>>> 
>>>>> 
>>>> Or +2.9dBm if using the 0.88v pk-pk I think is shown in the scope pic
>>>> rather than the 0.85v figure of your message.
>>>> 
>>>> 
>>> To CD:
>>> 
>>> The above is what I did. 30 + 10*log( (0.88/(2*sqrt(2)))^2 / 50) =
>>> 2.869 dBm. Rounded to 3dBm.
>> 
>> OK, thanks for that clarification. Anyway, I finally measured the power
>> of that oscillator with my HP RF power meter and it comes out at 1.74mW
>> (or about +2.5dBm off the top of my head). Seems a tad on the low side,
>> but I can't find what it's supposed to be in the manual.
>> 
>> 
>>> What's the issue with RMS vs. average?
>> 
>> When you dig into it, you find that what people really mean when they
>> talk about "RMS Watts" is actually *average* power. I found this on the
>> web which attempts to explain it:
>> 
>> https://agcsystems.tv/rms-power-fallacy/
>> 
>> 
> It’s really not this hard.
> 
> “RMS” stands for “root mean square”, which is a shorthand description of
> how you calculate the power delivered by an arbitrary voltage waveform
> (or equivalently current) in a resistive circuit.
> 
> You square the instantaneous voltage,  compute the mean (I. e. time
> average), and then take the square root.
> 
> All those fudge factors like 0.5, 0.636, 0.707, and so forth, can be
> useful for quick calculations, but they just summarize the results of
> the above procedure _for_specific_situations_. Without first doing the
> math, and understanding the situation, they’re worse than useless.
> 
> The ‘rms power’ thing came as a response to lying advertisements for
> stereo systems, starting in the 1970s iirc. Crappy stereos were
> advertised as producing “250 watts PMP”, for “peak music power”, as
> though that were a thing. That led to very optimistic numbers, even
> before actual lies were added, which they usually were.
> 
> People started pushing back by insisting on knowing what sine wave power
> the amp could put out continuously without distorting or overheating.
> 
> That’s a very conservative spec, since music waveforms have a high
> peak/rms ratio and the ear is most sensitive to transient distortion on
> the peaks.
> It does have some basis in reality, though, and is easy to measure
> unambiguously, which cuts through the Audio BS” (tm).
> 
> While saying “rms watts“ is indeed redundant, strictly speaking,
> nevertheless it’s a useful shorthand for describing audio amps, Chinese
> switchers, and (I suppose) power FETs.
> 
> Cheers
> 
> Phil Hobbs

Phil, I believe you also have an 8566B. Do you know what the 10Mhz 
reference oscillator output level should be? Is yours anything close to 
+2.5dBm?