I'm planning to make a project using the MX-FS-03V 433 MHz transmitter and the corresponding MX-05 receiver with a couple of Arduinos for short range radio communication. Range will be at most 10 meters.
I got a couple of these from Amazon, but one thing has me puzzled. This is a picture of the transmitter:
note that in the lower right corner are three unoccupied through holes. The extreme lower right one is where I will solder the antenna, but the other two have me puzzled. Looking at other pictures of this transmitter, there seem to be several revisions if the silk-screen on the PCB is anything to go by, and some have a second coil soldered between the two holes not used by the antenna, e.g. this one:
So what's going on here? I'm not that much of an expert, but I know enough to believe that removing a coil from an RF circuit is likely to have some pretty major effects. For one project, it is vital that I work at 433 MHz, so I'd like to have some idea of what I'm getting myself into.