# Comparision between BFSK and BPSK

Why is BPSK preferable over BFSK? On what parameters this comparison is based? What are the advantages of BPSK?

• Could you add a link, quote, or other reference to the claims you have seen that BPSK is preferable to BFSK? This will help give context for your question. Sep 4, 2015 at 14:21
• @KD8NXH What exactly is opinion-based in this question? Sep 6, 2015 at 8:27
• @KD8NXH Then wouldn't all questions expecting answers be opinion-based? Sep 6, 2015 at 16:01
• @AndrejaKo Sorry I didn't realize that there was actually some studies and researches into this question. I thought Shweta was just asking for our opinion. Sep 7, 2015 at 15:35

Unfortunately, I couldn't find a nice picture for this, so the one above from AtlantaRF will have to do, but in telecommunications literature, you have these bit error rate versus per bit signal to noise ratio graphs for various modulation schemes. One thing you always see in those graphs is that you need higher $E_{b}/N_{0}$ for same BER in FSK compared to PSK. In amateur radio, (clean) power is often relatively limited and getting more with less is respected, giving advantage to PSK.
For example, for non-coherent orthogonal FSK, the null-to-null bandwidth is $B=(M+1)R_{s}$, while for PSK (which is same as for non-coherent DPSK as used in say BPSK31) it's $2R_{s}$, so in binary case, we have $3R_{b}$ compared to $2R_{b}$ for BPSK. If number of modulation levels increases, FSK starts to lose very quickly, since in PSK case, bandwidth does not depend on number of modulation levels.