In a superheterodyne receiver, what must one consider in order to chose an intermediate frequency?
Specifically, I'm working on a radio telescope project. It is basically a superheterodyne receiver where the IF signal is 1-bit sampled and then stored.
The bandwidth of the signal is 20 MHz. Now, to minimize aliasing, I'll be using a sample rate somewhat above the Nyquist rate. That means the minimum sample rate is ca 50 MHz. The highest I could sample, on the other hand, is about 120 MHz.
This would however mean an IF range from 0 Hz to 20 MHz. If we drop the lowest 1 MHz, this equals to 4.3 octaves.
The observing frequency is 1421 MHz, if that matters.
I'm mostly worried about the high fractional bandwidth of the signal. So, my questions are:
Would it be problematic to amplify the 1-20 MHz (or even 0-20 MHz) signal using a high-speed OP-Amp (considering that many electronic components' behaviour is (inversely) proportionally dependent on the frequency)?
Is the high fractional bandwidth a problem? i.e. Would the SNR improve significantly if I used a 40-60 MHz range?
Low IF receivers are used to evade brown noise (noise power constant per octave) zero IF systems inherently suffer from. How much does it practically matter for an application like this?