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From: Cursitor Doom <cd999666@notformail.com>
Newsgroups: sci.electronics.design
Subject: Re: Distorted Sine Wave
Date: Sun, 2 Jun 2024 12:12:53 -0000 (UTC)
Organization: A noiseless patient Spider
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On Sun, 2 Jun 2024 13:00:21 +0100, John R Walliker wrote:

> On 02/06/2024 12:31, Cursitor Doom wrote:
>> On Sun, 2 Jun 2024 11:17:58 -0000 (UTC), piglet wrote:
>> 
>>> 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?
>> 
>> It wouldn't prove anything one way or ther other, though, since that
>> power meter hasn't been calibrated for "quite a while" so to speak. :)
>> It'll give a 'good enough' reading for my purposes, but won't be
>> accurate enough to meaningfully test your otherwise fine suggestion.
> 
> I have an 8566B which is currently not working.  Both the status leds on
> the front panel at the bottom are red.  I haven't started to investigate
> yet.
> The fault developed slowly.  At first it would sometimes work, then
> progressively less often and now never.
> However, if the signal being discussed is available on the rear panel I
> could measure mine and see what it looks like and what voltage is
> delivered.
> John

Yes, that could be very helpful, John, since your fault is clearly totally 
different to mine. Peak to peak volts into 50 ohms on a scope will be fine 
if don't have access to an RF power meter.