[Elecraft] Anne Marie Sullivan and Logs (XG-1 Question)

[John R. Lonigro]

Tom:

Your confusion is warranted.  Here's the problem:

Looks like the example in the manual has some typos in it.  He 
calculates (S+N)/N to be 33.  So far, so good.  In step B, he somehow 
uses 30 instead of 33, but the answer (1.52) is the log of 33.  1.48 is 
the log of 30.  It looks like he was going to use 30, but switched to 33 
(or vice versa).  Anyway, in the example, step C should be multiplying 
1.52 by 20, which gives about 30.  Step D is correct that the MDS is 
approximately -137 dBm.

In your case, 0.59/0.016 is 36.875.  The log of 36.875 is about 1.57.  
Multiplying by 20, (S+N/N) is 31.33 dB at 1 microvolt.  Finally, since 
31.33 is greater than 10, MDS is -107 - 31.33 or about -138 dBm, almost 
the same as the example.  If your MDS were -198 dBm, you'd have one heck 
of a hot receiver.

Hope this helps.  As you know by now, women and math don't mix, 
especially in high school.

73's,

John AA0VE


Tom Mc wrote:

>Hi guys,
>
>  Well I'm trying to determine the MDS of my K2 and it seems that during
>High School trig I spent more time daydreaming over Annemarie Sullivan than
>learning logarithms.
>
>So could someone please help me out.
>
>The readings I'm getting from the K2 are N (Noise only no XG1 ) about .016
>Vrms.  and S+N (Signal and noise with the XG1 on at 1 uV) of .590 Vrms.
>
>Well I do all of this and I come out with an MDS of -198, which is pretty
>stinky, I think.
>
>I should also admit, that the example in the manual is totally mystifying to
>me as it seems to be using numbers that just appear out of thin air (e.g.
>if Step "B" says log(30) = 1.52, then why are they using 1.48 in step "C"?
>And what the heck is the 30 in "log(30)".) -- OK I know, I should have paid
>attention in class, but ohhh you should have seen Annmarie.
>
>  
>