[R-390] R390 not A calibrator issue

Sun May 26 11:49:08 EDT 2019

Hi Jacques, and thanks again!

I used a 100x, 250 MHz scope probe, then I switched to a 700 MHz, 10x probe since the voltage wasn't so high into my Tektronix 2465 (found those 700 MHz Keysight probes at a yard sale NIB.)  I also tried it with a DC block into the scope in 50 ohms mode.  But that loaded it down too much plus my DC block is only good down to around 300 kHz into 50 ohms.  

I too thought it should look more like a square wave, lopsided of course, to get the even harmonics too.  I wondered, since it looks like a sine wave sort of, that it just drove the first RF amp into saturation/cutoff and the harmonics got generated there.  I'll have to go back and look at it.  I was surprised that my calibrator's multivibrator didn't output a pseudo square wave.  The TM's don't seem to have any information on proper operating voltages and waveforms, even for the depot guys.  I guess I'm just spoiled having modern equipment that is common versus the old days when having more than an Eico round screen, one channel, 1 MHz scope was a luxury.

Yes, I am using TM 11-5820-357-35.  My RF deck is stamped as having a MOD, but right now the radio is flipped over while I work on the B+ issue.  I'm too lazy to flip it over right now to look at what MOD # it has.  😊

Is the MOD 4 stuff worth doing?  Does it make a big difference?  If so, I'll tear into the RF deck.  I've attached a snapshot picture of the mod list from my TM copy.  Does it look about right?

Thanks again sir!
John

-----Original Message-----
From: Jacques Fortin <jacques.f at videotron.ca> 
Sent: Sunday, May 26, 2019 10:28 AM
To: jgedde at optonline.net; 'r390a' <r-390 at mailman.qth.net>
Subject: RE: [R-390] R390 not A calibrator issue

Hi John,

Your sentence: I get a strong, reasonable looking 100 kHz sine wave out on the scope....
Made me tilt...
Where and how (what type of probe) did you measure this 100kHz sine wave ??
Normally, the output of the calibrator SHOULD NOT be a sine wave: it is usually a weird, peaky waveform, on purpose.
Because that waveform have to contain all the even and odds harmonics up to the 300th, at least.
More the waveform looks like a "perfect" sine wave, less harmonics it contain.
The receiver problem can be also the C226 that is open, or been removed by someone...
Not sure you will escape a trip inside the RF deck for long...
BTW, which manual are you using ? The TM 11-5820-357-35 ??
You can see in the first pages that there is a lot of changes needed to bring the RF deck up to the MOD 4 status.

73, Jacques, VE2JFE

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