Signal response in Frequency Hz from angular frequency I have a filter whose respose I have in angular frequency. 

A0 = [1.0000000,0.3281250,0.0000000];
B0 = [0.5859375,-0.0625000,0.0000000];
[z,p,k]=tf2zp(B0,A0);
figure;
zplane(z,p);
w = 0:(pi/500):pi;
H=freqz(B0,A0,w)
figure;
plot(w,20*log10(abs(H)/max(abs(H))))


1) How can I get the corresponding response in Hertz? Is it:

plot(w/(2*pi),20*log10(abs(H)/max(abs(H))))


2) Also, how do I get the response of the above filter, if I apply it to a sinusoidal signal at 20MHz, with a sampling freq of Fs=300MHz
have a look to this example: http://www.mathworks.com/matlabcentral/fileexchange/55822-low-pass-filtering

here you have a signal that can be represented/plot in both frequencies scales:

omegas_axis=[0:2*pi/L:2*pi-2*pi/L];%axis input signal
frec_axis=[0:fs/L:fs-fs/L];%axis input signal


the "omegas_axis" is the angluar frequency.

Hope this helps,

BTS.