FM sens - DX versus Local. Huh?

I have a Sony Walkman style FM radio that has a switch on the side that reads “FM SENS” - the switch can be set to DX or Local. If I’m just walking around outdoors, “local” gets good reception. But if I’m indoors or an enclosed place (even at my gym which is in a basement) I can switch it to DX and get reception! On the flip side, DX doesn’t work outdoors and Local doesn’t work well indoors.

Okay, so if anyone knows anything about radios, fill me in. What is DX, what is local, why does one only work indoors and the other only works outdoors. It seems if DX can pick up a signal in a basement, it should be able to pick up a signal on the street.


On “local” it filters out weaker signals and only picks up stronger ones, ie a local station. In DX mode, it picks up more distant stations.

Yeah, it’s all to do with sensitivity. DX (radio shorthand for ‘distance’) is akin to putting in a hearing aid: You hear everything, but close sounds are too loud to do you much good and if you are in a loud place every sound just swamps every other sound, leading to a lot of noise. Local is like removing the hearing aid: You hear things in your immediate area very well, but noises from far off are just too faint to make out.

DX tends to eat batteries if you use it much though. (Or have I just run into a pack of bad batteries?)

DX is obtained by increasing the gain on the antenna/tuner section of your radio.

To use a TV antenna analogy, gain can be increased in three ways. The first is to use a relatively simple amplifier to boost signal strength down the cable to the tuner circuitry - ie a masthead amplifier (also known as a booster).

The second way is alter the design of the antenna to make it more directional and to match it more precisely with the desired frequencies. Most TV antennas are designed to pick up a wide range of signal over a broad arc.

The third way is to increase the sensitivity of the tuner circuitry, but that may require it to be better at screening slightly-out-of-tune signals - the rtrade calls this narrowing the bandwidth. All radio signals occupy a small range of frequencies above and below the nominal value. Better receivers ensure that the bandwidth is more precisely matched to the spread of frequencies.

Hope that satifies your curiosity.