What is the difference between RP-SMA and SMA connectors, and why are they both necessary? First, it is important to note common uses:
RP-SMA: Primarily WiFi and Helium but also Meshtastic, IoT
SMA: Primarily Meshtastic, LoRa, IoT, and Cellular
SMA and RP-SMA look very similar but are NOT interchangeable. RP-SMA stands for "reverse polarity SMA" and gender goes by threading. SMA male connectors have a pin, but RP-SMA male have a center hole. SMA female have a center hole while RP-SMA female have a center pin.
SMA connectors were introduced in the 1960s as a name change to the BRM connector developed by James Cheal in 1958, and are commonly used in radio and communication equipment.
Contrary to popular opinion, RP-SMA (which stands for reverse polarity SMA), was not developed to make consumers go crazy. WiFi equipment manufacturers needed to develop equipment with connectors that would not breach FCC EIRP restrictions. RP-SMA was developed as a solution.
RP-SMA looks nearly identical to SMA but the pin and hole are inversed. Therefore RP-SMA male have a center hole, while RP-SMA female have a center pin. Gender goes by threading with RP-SMA, even though we are used to gender being related to pin and hole.
For most Rokland WiFi and Helium hardware, the connectors will be RP-SMA so that manufacturers will be in compliance with the FCC EIRP rules. Other radio equipment we sell, such as our LILYGO hardware for Meshtastic, uses SMA connectors. If you buy the opposite cable from what you need,. you can get this barrel converter to flip to the other type.
The converter is a must-have for anyone in radio, especially hardware devs, as sooner or later you will find yourself holding an SMA female device and an RP-SMA antenna or cable.
Military and First Responder 
