[Elecraft] XG1

[Donald Nesbitt]

Hi Ken - thanks for the info.  This is beginning to make some sense to me.
If I look at the 600 Hz audio spike produced by the known 1 microvolt rf
input signal using either Spectrogram or Spectrum Lab with the rig set up
for testing as per the manual (on 7040 etc where the sig is close to 1
microvolt), then the top of the 600 Hz blip ought to represent -107 dBm.
Now for the leap - if I then measure the difference between the top of the
blip and the bottom of the blip - where it disappears into the "noise" on
the "shoulder" and subtract that from -107 I ought to have the MDS (or close
to it) from the visual indicator and it ought to agree (within reasonable
limits) of the value that I get by calculation.  Guess what!  It does!  By
calculation I got -142 dBm with preamp on and by using both Spectrogram and
Spectrum Lab for the "visual" method, I get -144 dBm.  Close enough for
government work!  The preamp-off test shows about the same amount of
agreement.

When I go to 20 and take into account that the top of the blip would be 7 dB
down from 1 microvolt, and do the same thing, I get similar agreement!

Surely there is a flaw in my procedure somewhere (and I'm sure someone will
point it out - at least I hope so) but it seems to make sense to me!    It
has been 45 years since I began a career in EE and quickly switched to
something else.  I discovered very quickly that I liked to "play" with
electronics and not work with it!!  Thanks for your help.  73  --don

----- Original Message ----- 
From: "Ken Wagner" <kewagner@ids.net>
To: "Elecraft Reflector" <elecraft@mailman.qth.net>
Sent: Thursday, January 29, 2004 5:44 PM
Subject: [Elecraft] XG1


> A comment in an earlier email wondered where the -107dBm came from. From
an
> old handbook, I pulled the following:
>
> dBm = 10 log {20*(Vrms)^2}
>
>  where "log" is base 10
>
> If you plug in the 1 microvolt into that equation and solve it, you cill
> come up with -107dBm. Please don't ask me to derive the equation <g>. Too
> many years have passed....
>
> 73
> Ken Wagner
> K3IU
>
>
>
>
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