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Re: AO-40 spreadsheet



I pulled out my copy of the Manual to correct the formula, but
I got really confused after reading it.
The way it is laid out and parenthesized, I cannot really figure out
how to properly evaluate it.  (I think there is a good reason why
they stopped using "x" for multiplication after 9th grade...).

Also, the way I interpreted Ed's correction, it looks like the
result would be undefined if L3 was 1, since you would be dividing by zero.

Finally, I just noticed that T3 does not appear anywhere.

If I needed to actually do the calculation, I would feel a lot
more confident grabbing it from a known-good spreadsheet.

Doug
Na1DB

At 10:48 AM 5/28/01 , you wrote:


>Domenico also refers you to Bob Atkin's, KA1GT, article "Noise Temperature,
>Antenna Temperature and Sun Noise"  published in The ARRL UHF/MICROWAVE
>EXPERIMENTER'S MANUAL.  Bob's articles are good reading on the subject,
>however there is an error in Bob's noise figure formula on page 7-57.  It
>will give you fits if you are using it to evaluate your system.  This
>article was originally published in QST in the 1980's and the error has
>escaped correction and been copied often.  The problem lies in the third
>coax cable loss expression T(L3-1).  It should be: T*L1*L2/G1*G2*(L3-1).  
>
>I have a noise figure/MDS Excel spreadsheet [cascade.xls] that computes
>system noise temp/NF for you:  http://www.setileague.org/software/spreadsh.htm

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