Re: Distorted Sine Wave

On Sun, 2 Jun 2024 20:05:43 +0200, Jeroen Belleman wrote:

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

Sorry, but I don't recall anyone claiming average power and average
voltage were the same thing!