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  #16  
Old 02-08-2012, 08:46 PM
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JohnHacker1 JohnHacker1 is offline
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Congrats on the acquisition-it's funner to test/align old stuff with old stuff.
But...
Isn't that a rather non-linear sine-wave?
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  #17  
Old 02-08-2012, 09:13 PM
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Actually, that's pretty darn good for an inexpensive, vintage tube based generator. Also, often they were designed to have harmonics for the high bands which distorts the sine wave a bit.
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  #18  
Old 02-11-2012, 12:26 PM
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Kevin Kuehn Kevin Kuehn is offline
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Yeah, the accuracy of the generators sine wave is really of little importance for doing visual sweep alignment. What your looking at is the detected pass band of the receiver, so you can about throw any noise at it, as long as the RF sweeping frequency can be synced to your scope.
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  #19  
Old 02-19-2012, 02:12 PM
FrankieKat FrankieKat is offline
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I went ahead picked up a WR-50B, and running it through the paces. Putting up on the scope, I'm noticing that the output seems a little bit off. Or is this the low frequency distortion mentioned earlier?

For example, here is what I get when I do a simple sine wave:



Notice how flat the lower cycle is compared to the top. Also, when I do sweep mode, the blanking period is definitely not flat:



And when I plot them both with the second being the output of my homebrew Sencore SG-165 demod probe, I get the following -- note the spike at the beginning of the sweep... related to the above?



I wondering then, if this is an issue of basic calibration or if I should re-cap it first and then try a calibration?

Edit: Both tubes test excellent on my emissions tester. I've also found that different frequencies and different ranges have different levels of distortion, so wondering if it might be a calibration issue then. Also, I've found that if I turn the ON/OFF MOD past about 12:00, the modulation frequency goes down... hmm.
Attached Images
File Type: jpg sweep2-web.JPG (115.3 KB, 31 views)
File Type: jpg sweep1-web.JPG (101.6 KB, 28 views)
File Type: jpg sine-web.JPG (110.6 KB, 30 views)

Last edited by FrankieKat; 02-20-2012 at 12:21 PM.
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  #20  
Old 02-21-2012, 11:22 PM
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Those waveforms look pretty good to me. This is a fairly simple design and some distortion is to be expected. The original brown caps I believe are fairly reliable so didn't bother to recap.
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