[R-390] R-390 sensitivity measurements

[Bob Camp]

Hi

As with many things, what matters the most in sensitivity measurements 
is that you define how you got your numbers.

There are a number of ways to change the setup that will impact the 
result that you get. That's neither good or bad in it's self. What is a 
problem is a undefined method. If I use method A and you use method B 
we really can't be sure that the results are comparable to each other. 
If we each have fully characterized and defined (no small task) our 
methods then we may be able to guess at a comparison.

A lot of restoring these radios comes down to "I got 0.001 uv on all 
bands, time to tell the world".  I think that has lead to a number of 
conversations about measurement technique ....

A far more interesting question - does *any* single sensitivity number 
actually tell what's going on in the real world? I would claim that the 
answer is no and that is the root of the problem. At that point (no one 
number)  we more or less divide into those who give up on numbers and 
those who measure a whole bunch of numbers. That makes for interesting 
conversations ....

	Take Care!
	
		Bob Camp
		KB8TQ




On Jan 16, 2005, at 10:46 PM, DJED1 at aol.com wrote:

> Here's another bit of trivia which I hope will entertain.   In looking 
> at
> Dallas' other postings, he discusses a method of measuring receiver 
> sensitivity.
>  From my view, I'm not sure there is an absolute correct way, but just 
> for
> fun I looked up the MIL spec for the R-390 (MIL-R-13947B) to see what 
> the test
> requirement was.   It's pretty close, but not exactly what Dallas 
> discussed.
> The spec has two tests: AM and CW.   The AM is performed by turning the
> generator modulation on and off, with 30% at 400 cycles modulation.   
> The signal
> level is set for 10 mw audio out with modulation, and 1 mw with no 
> modulation.
> The only difference from his test is that it is done at 8 Kc 
> bandwidth, and a
> 125 ohm matching resistor is in series between the generator and the 
> receiver.
>   You still need to do the correction for the generator reading to get 
> the
> voltage at the receiver.
> For the CW case, the setup is the same, except the generator is 
> unmodulated,
> where signal is carrier on and no signal is carrier off (still in the 
> 8 Kc
> bandwidth).    The AM spec is 3.3 uv except in the 16-32 bnd, where it 
> is 4.4 uv.
>   The CW spec is 1 uv.
> This, I believe, was the final spec for the R-390 and was used for 
> acceptance
> testing.   I never did much like the concept of turning the modulation 
> on and
> off, but this gives that approach significant legitimacy.
> Ed
>
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