[DSP-10] Receiver system temperature

[Perry Ogletree]

What type resistors did you use?  I suspect you may have a non-linear noise 
factor in the resistors coupled with accumulated measurement errors.  Did 
you heat the resistors in a "bath"?  If you used hot air, what did you do to 
insure even heating of the resistors.
You might want to take your samples at 0C and at 20C and see how it measures 
up.

----- Original Message ----- 
From: "Courtney Duncan" <cbduncan at earthlink.net>
To: "DSP-10" <dsp-10 at mailman.qth.net>
Sent: Sunday, October 01, 2006 1:44 AM
Subject: [DSP-10] Receiver system temperature


> 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
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