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From: Jeroen Belleman <jeroen@nospam.please>
Newsgroups: sci.electronics.design
Subject: Re: Distorted Sine Wave
Date: Sun, 2 Jun 2024 13:49:16 +0200
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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.

What's the issue with RMS vs. average?