Path: ...!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail From: Cursitor Doom Newsgroups: sci.electronics.design Subject: Re: Distorted Sine Wave Date: Sun, 2 Jun 2024 12:12:53 -0000 (UTC) Organization: A noiseless patient Spider Lines: 81 Message-ID: References: <3lcf5jd7li0a3c0fgddt7o8lnfocvls2pr@4ax.com> <48bd78e1-7da8-3bba-2879-d22962203fa3@electrooptical.net> <9olh5j9al34fhrebr4grqq8h6c8javjpp1@4ax.com> <1n0i5jh257hiinlj2dhaatlo11s33m5n0e@4ax.com> <9k2i5jpfhu3ncfpm28ukusrok4hugal80s@4ax.com> <9tok5j9p388ookujrtbsofskjlbekfuhjb@4ax.com> <60rk5jti9l5154hqaqicohmj3u1lfd16g3@4ax.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Injection-Date: Sun, 02 Jun 2024 14:12:53 +0200 (CEST) Injection-Info: dont-email.me; posting-host="40a1d383888994c45f6bff6cd4b36ba9"; logging-data="3519815"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX18NTEZOd685/Jq8CVyhSe7dDbxGN45vRrA=" User-Agent: Pan/0.149 (Bellevue; 4c157ba) Cancel-Lock: sha1:q5/OPpq07UujFs2lR44smx1xOLk= Bytes: 5409 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 wrote: >>>> On Sat, 1 Jun 2024 22:00:58 -0000 (UTC), piglet wrote: >>>> >>>>> Cursitor Doom 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.