[DSP-10] Receiver system temperature

[Courtney Duncan]

I've just measured the receiver temperature of my DSP-10 in the following way:

Solder a pair of 100 ohm resistors in parallel at the end of a piece 
of coax with a BNC on the other end.

Connect this to the DSP-10 antenna connector in receive mode.

Measure the bulk temperature of the pair of resistors by inserting 
the thermocouple from a BK Test Bench 390 in between them.

Captured a minute of data in CW mode with this terminator at 20C (293.16K).

Warmed up the resistor pair to 101C (374.16K) and took another minute of data.

Did two other such data captures, one at 105C (plus or minus 5) and 
another at 20C.

Sum up all 255 bins of noise over each file and calculate the implied 
receive noise temperature using the formula:

P2m / P1m = R = ( Tr + T2 ) / ( Tr + T1 )

Where R is the power ratio between the warmer ( T2 ) and cooler ( T1 
) measurements and Tr is the unknown receiver temperature.

I'm assuming that I can just add the temperature of the receiver to 
the temperature of the load like this.

This reduces to

Tr = ( T2 - R*T1 ) / ( R - 1 )

My four measurement files are:

Temp.   Power average
20C     3.87855
20C-2   4.01719
101C    4.17844
105C    4.25063

Using 20C and 101C, I get Tr of 754K.
Using 20C and 105C, I get Tr of 593K.
Using 20C-2 and 105C, I get Tr of 1170K
Using 101C and 105C, I get nonsense.

This is admittedly this is a "noisy" measurement, but the results are 
not inconsistent with either 600K or 1000K.  Based on this, I think 
I'll keep using 600K for calculations for now.

Does anyone recall offhand what the spec sheet for the first RF 
amplifier says about its noise figure?

Courtney, n5bf/6