Re: Distorted Sine Wave

On Sat, 1 Jun 2024 22:00:58 -0000 (UTC), piglet 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 ?

Thanks, Erich. But there's no such thing as "RMS power" strictly speaking
IIRC, so that's why I took the average figure; not that it makes much
difference in practice. it does seem a bit on the low side, but despite
reading through the most likely sources (the service manual and the
trouble-shooting/repair manual) I can find nothing stated for what that
signal level should be! This may be due to the user-unfriendliness of very
large PDF manuals; I just don't know. Anyway, not very satisfactory! Later
today I plan to do a direct power meter measurement of the ref osc (since
none of us here seem to agree on what 850mV vs 50 ohms equates to!!)