[R-390] R390A sensitivity and noise floor measurements

[Cecil]

Ripple used pixie dust....

Sent from my iPad

> On May 5, 2019, at 3:24 PM, <jgedde at optonline.net> <jgedde at optonline.net> wrote:
> 
> After weeks of fiddling, tube swap optimizations, fixes, etc. I've got my
> R390A performing extremely well.  I have an HP 8644A signal generator I
> bought from the local scrap dealer for scrap value (it works fine) and was
> able to make the following measurements:
> 
> 
> 
> Sensitivity: 0.55 uV for 10 dB S+N/N with a 30% modulated input.  It'll do
> better with 100% modulation..
> 
> 
> 
> Noise floor: better than -137 dBm.  I can't go any lower with the 8644A
> without additional attenuators (they appear to add noise of their own) and
> my noise environment isn't great.  A screen room would be needed to go any
> lower.  I fiddled a bit with the IF gain and got an improvement from -132dBm
> with the standard IF gain setting at -7V at the diode load to -137 dBm.  The
> judging factor was whether the signal could be detected.  At -137 dBm you
> could just make out that the sig gen was on or off.  My spectrum analyzer
> can go much lower in noise floor and confirms I wasn't just measuring RF
> leakage in the sig gen: it can see -137 dBm no problem if I set up the BW
> just right.
> 
> 
> 
> While I am not able to repeat Chuck Rippel's -143 dBm and Sherwood
> engineering's 0.2 uV, I consider this quite good and I am very pleased.  But
> to be fair, Sherwood doesn't state what they used as a source.  If it was
> 100% modulation, then I was able to get there.  I used the 30% modulation
> standard.  I tend to doubt -143 dBm noise floor to begin with as I have
> stated before.  I wonder if his sig gen is leaky?  Sherwood got -137 dBm as
> did I.
> 
> 
> 
> Another good R390A day!
> 
> 
> 
> John
> 
> 
> 
> 
> 
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