[R-390] Measuring tangential sensitivity

[Mark Huss]

Bill, you are right. It's most common use is to test the Signal to noise 
ratio of video and wideband amplifiers and detectors. It is also used in 
Cable TV Amplifiers. And in Radio Telescopes. It is not often used in HF 
receivers because there is no way to really adjust the system noise 
floor in them. The R-390 and R-390A, with their IF Gain adjustment which 
not only adjusts the total receiver gain for matching purposes, but also 
has a large effect on the receiver noise floor, are exceptions to this rule.
I first ran across this technique at Capitol Cable in Austin back around 
1972. I was reintroduced to it again when being trained to repair 
R-390's in ASA School. And later when doing VHF/UHF and Satcom systems.

Before you reject it out of hand, give it a shot. The only thing you are 
adjusting is the IF Gain pot. It is easy enough to adjust it back if you 
find it does not help your receivers noise floor.

Bill Hawkins wrote:
> Roy,
>
> Seems like I was off the mark. As is usual, one should do some
> research before hitting the keyboard, unless one's intent is to
> liven things up a bit.
>
> >From a blurb for Agilent wide range laboratory detectors:
>
> "Tangential sensitivity is the lowest input signal power level
> for which the detector will have an 8 dB signal-to-noise ratio
> at the output of a test video amplifier. Test amplifier gain
> is not relevant because it applies to both signal and noise.
> Agilent detectors are designed for optimal flatness and SWR."
>
> Since R-390s do not contain video detectors, I let the matter drop.
>
> Regards,
> Bill Hawkins
>
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