Because of the high maintenance needed to monitor and filter spammers from the RF Cafe Forums, I decided that it would
be best to just archive the pages to make all the good information posted in the past available for review. It is unfortunate
that the scumbags of the world ruin an otherwise useful venue for people wanting to exchanged useful ideas and views.
It seems that the more formal social media like Facebook pretty much dominate this kind of venue anymore anyway, so if
you would like to post something on
RF Cafe's
Facebook page, please do.
Below are all of the forum threads, including all
the responses to the original posts.
SmokingJoe
Post subject: available noise power consistency check
Posted: Sat Sep 10, 2005 8:42 am
Lieutenant
Joined: Sat
Sep 10, 2005 8:04 am
Posts: 1
Hi all,
I was reading up
on noise power and etc, and I understand that 4KTR*delta_f is the maximum
power transmitted(available noise power) for a resistor with a matching
load resistance. Unless I miss read between the lines, if the load resistance
is NOT = to the source resistance, then the above equation is no longer
valid.
Now the problem I ran into is this: after a few more pages,
I found a simple Thevenin eq circuit containing Source V and R, and
a load C. Now Vo^2 is the noise power across the Capacitor and Vs^2
is the noise power input. Thus, Vo^2 = Vs^2 / (1 + jwRC)^2. Now my first
question is:
I thought P(load) = Vs^2 x Resistance(load) / Impedance(total),
and since the output impedance is modeled by just the capacitor, there
shouldn't be a real resistance value at all, but the above equation
applies (1/sC) as the output resistance and I don't know why. I thought
(1/sC) is the complex part of the impedance and should not be utilized
in the above Noise power equation?
And then the book replaces
Vs^2 with 4KTRdf, so:
[b] I thought 4KTRdf is only valid when
the R_load matches the R_S, so what makes the author perform the above
subsitution?
_________________
I am a fourier illiterate...
Posted 11/12/2012