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: Jeroen Belleman Newsgroups: sci.electronics.design Subject: Re: Distorted Sine Wave Date: Sun, 2 Jun 2024 20:05:43 +0200 Organization: A noiseless patient Spider Lines: 71 Message-ID: References: <3lcf5jd7li0a3c0fgddt7o8lnfocvls2pr@4ax.com> <48bd78e1-7da8-3bba-2879-d22962203fa3@electrooptical.net> <9olh5j9al34fhrebr4grqq8h6c8javjpp1@4ax.com> <1n0i5jh257hiinlj2dhaatlo11s33m5n0e@4ax.com> <9k2i5jpfhu3ncfpm28ukusrok4hugal80s@4ax.com> <9tok5j9p388ookujrtbsofskjlbekfuhjb@4ax.com> <60rk5jti9l5154hqaqicohmj3u1lfd16g3@4ax.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Injection-Date: Sun, 02 Jun 2024 20:03:40 +0200 (CEST) Injection-Info: dont-email.me; posting-host="e56d717ab3cbbbe261a1c19c41844c4c"; logging-data="3645227"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX183NTBbRjOvWi9xxdbJy8Xz" User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.13.0 Cancel-Lock: sha1:GNcYHE6CXsmFyNbQxd8T6dFKXC4= Content-Language: en-US In-Reply-To: Bytes: 4513 On 6/2/24 14:09, Cursitor Doom wrote: > On Sun, 2 Jun 2024 13:49:16 +0200, Jeroen Belleman wrote: > >> On 6/2/24 00:24, piglet wrote: >>> 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! >>>>>>> >>>>>>> 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/ Average power is not the same as average voltage! Average power is proportional to the average of the voltage squared. It makes a difference! Jeroen Belleman