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From: kalam_gre AZED on 19 May 2010 19:21
Hello there,
i am a bit confused about dB conversion, i got an equation which consist of two parts
say P and C, where P is the Power and C is the constant (it doesn't have any power), which have impact on the power. so if i want to convert to db the whole equation

so which one is correct ===

a. Result= (10*log10(P)) * C
b. Result= (10*log10(P * C))

i am giving the code i did as (b), result is not perfect cas it meant to be decreasing with time and (a) is not perfect at all i think, can you please have a look.


syms c d y t;
c=3*10^8;
freq=60*10^10;
T1=5*1e-6;
Am=(c*T1)/2;
d=100;
Bm=0.5*sqrt(((c*T1)^2)-(d^2));
Lamd=c/freq;

t=3.3*1e-6;
while (t<=T1)
f1=(d^2*c+t^2*c^3-2*t*c^2*cos(y));
f2=(d*cos(y)-t*c)^3;
f3=f1/f2;
f4=(1/(4*pi*Am*Bm))*(Lamd/(4*pi*d))^2*10^.05*(d^2+t^2*c^2);
PDS_DB=f4*2*int(f3,y,0,2*pi);
plot(t,10*log10(double(PDS_DB)),'r-o');
hold on
t=t+1e-8;
end
grid on
xlabel('Delay (usec)');
ylabel('PDS [dB]');


From: dpb on 19 May 2010 20:38
kalam_gre AZED wrote:
> Hello there,
> i am a bit confused about dB conversion, i got an
> equation which consist of two parts
> say P and C, where P is the Power and C is the constant
> (it doesn't have any power), which have impact on the power. so if i
> want to convert to db the whole equation
>
> so which one is correct ===
> a. Result= (10*log10(P)) * C
> b. Result= (10*log10(P * C))
....

b.

Express the engineering units in dB (altho the result of a. will be
proportional, it won't be normalized as expected)

--
From: kalam_gre AZED on 19 May 2010 21:17
dpb <none(a)non.net> wrote in message <ht20dn$oio$2(a)news.eternal-september.org>...
> kalam_gre AZED wrote:
> > Hello there,
> > i am a bit confused about dB conversion, i got an
> > equation which consist of two parts
> > say P and C, where P is the Power and C is the constant
> > (it doesn't have any power), which have impact on the power. so if i
> > want to convert to db the whole equation
> >
> > so which one is correct ===
> > a. Result= (10*log10(P)) * C
> > b. Result= (10*log10(P * C))
> ...
>

> b.
>
> Express the engineering units in dB (altho the result of a. will be
> proportional, it won't be normalized as expected)
>
> --

i also realized that (b) is correct process, now the problem is the dB is getting higher with time (which should be opposit). i can't understand why its getting like that ...

cheers
kalam
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