# Improving RF sensitivity

I'm trying to improve the range on my 433 MHz radios that are using the CC430F5137.

Based on 25.3.3 in http://www.ti.com/lit/ug/slau259e/slau259e.pdf, it seems like decreasing the RX filter BW can improve radio sensitivity. I looked over TI's DN005, DN015 but I didn't see an explanation why this was the case. Common sense tells me that if you're listening over a larger spectrum, the radio has less time to distinguish between signal and noise. But that's not a satisfactory scientific answer, is it?

Based on (3) in http://www.ti.com/lit/ug/slau259e/slau259e.pdf, decreasing the baud rate helps radio sensitivity as well. Again, this makes sense since there is more time for each 0 and 1 to transmit over the air. Is there any scientific explanation for this as well?

I guess the other question is if the baud rate is related to the RX filter BW. Or are they completely orthogonal concepts?

Common sense tells me that if you're listening over a larger spectrum, the radio has less time to distinguish between signal and noise. But that's not a satisfactory scientific answer, is it?

Your common sense is flawless. A generally accepted formula for receive sensitivity is: -

Sensitivity = -154dBm + 10$log_{10}$(data rate)

So, at 1Mbps the receiver's best sensitivity is -94dBm. For 1kbps this becomes -124dBm.

There are several factors that go into this including temperature of receiver but at or around ambient this formula is pretty useful. Temperature produces noise and background thermal noise is ultimately what you are fighting against (plus interference from other transmissions).

If you want more theory, then the essentials of radio wave propagation is the best source I've come across. See page 14.

To make use of the higher sensitivity, a receiver's bandwidth has to shrink to suit the smaller bandwidth of a lower baud rate transmission.

• Thanks for the answer! But shouldn't sensitivity = f(data rate, bandwidth)? The wikipedia article on sensitivity (en.wikipedia.org/wiki/Sensitivity_%28electronics%29) gives another equation. So, I assume the sensitivity equation you shared is some approximated version? Commented Dec 22, 2014 at 3:42
• The equation above assumes that the bandwidth of the receiver diminishes for lower data rates. Commented Dec 22, 2014 at 8:52