Re: Distorted Sine Wave

Cursitor Doom <cd999666@notformail.com> wrote:

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!!)
 
 
 
 

Since you have a power meter, a signal source, and an oscilloscope why not
measure the peak to peak voltage on the scope and power on the power meter
and see which calculation 0.636 vs 0.707 gives the closest agreement?


--
piglet