Path: ...!news.mixmin.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: Sun, 2 Jun 2024 12:09:48 -0000 (UTC) Organization: A noiseless patient Spider Lines: 64 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 Content-Transfer-Encoding: 8bit Injection-Date: Sun, 02 Jun 2024 14:09:49 +0200 (CEST) Injection-Info: dont-email.me; posting-host="40a1d383888994c45f6bff6cd4b36ba9"; logging-data="3519815"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX19hwoKInez1pJCOuxNXeXr7EhRvv6JfD88=" User-Agent: Pan/0.149 (Bellevue; 4c157ba) Cancel-Lock: sha1:jK34xCByKpHVF8DX1FFD3OKhfBU= Bytes: 4046 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/