Re: Distorted Sine Wave

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 <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/

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