Ever wonder why some scanners have different type of antenna connectors? Ever wonder what BNC, SMA or PL259 stand for? Read on and learn!
Most scanners these days have either a BNC or an SMA antenna connector. BNC’s are the ones with the round barrel (about the same diameter as a pencil) and 2 little nubs that you twist on and off to. SMA’s are smaller threaded connectors. Both SMA and BNC mounts have a small center conductor that is surrounded by a ground that is the barrel.
Why are these used for scanners? Well, it is because they work well at a reasonable cost. For years the BNC has been pretty much the standard scanner antenna connector, replacing the old “Motorola” antenna connect that had been around since dirt was invented. Some old scanners used the “UHF” connector. Almost all scanners over the last 10 years or so use either the BNC except for some handhelds that use the SMA.
Until scanners started to standardize on the BNC handhelds use a wide variety of connections, including several different threaded connectors, earphone style plugs and permanently mounted antennas. Most mobile or desktop scanners used Motorola connectors since these were also used on most car radios. Some old scanners used SO-239’s (the female part of the UHF connector), which were common for CB’s and other two-way radios. By the 1980’s many scanners started showing up with BNC’s, both handhelds and base/mobiles.
As handheld scanners shrunk in size some started having SMA connectors replacing the BNC’s. This save a bit of room but forced the manufacturers to produce new antennas and include adaptors. Some scanners that have SMA’s also come with a BNC adapter to allow you to use your existing BNC antennas and accessories, ScannerMaster also sells these adapters.
BNC’s is a bayonet type connection. These press in, with the nubs fitting into grooves. They get locked in with a slight twist and this provides a good physical and RF connection.
SMA’s are a fine threaded connection, the connector itself is smaller than the BNC, both inside the radio and out. With smaller radios, like the BCD396 series, this little bit of extra space helps. Since most scanner users already have BNC antennas, coax connectors and accessories, the manufacturers often include an SMA to BNC adapter to let you use all your existing goodies. Some high-end radio receovers come with “N” connectors. Look close at these and you might notice that a male “N” connector will fit onto a female BNC. They were developed by the same guy, the “N” in both connectors comes from his last name: Neill.
BNC connectors get their name from the bayonet layout (“B”), and the developers, whose last names started with “N” and “C”. SMA stands for “Sub-Miniature Type A”. There are also SMB and SMC but you will likely never see one.
Many two-way radios these days use “Mini-UHF” connectors, these are smaller versions of the venerable UHF connectors. “UHF” connectors actually do not work well on UHF frequencies. The original UHF connector was so named before WWII, when anything about 30 MHz. was a radio wasteland suitable only for hobbyists and experimenters.
All these connectors come in a Male or Female version. This is based on the center pin/socket. The connectors with a pin are male. The UHF connector is a little odd, in that it has common names for the distinct parts. The SO-239 is the female, used on the radio while the PL-259 is the male used on the coax. “SO” stands for Socket, “PL” stands for Plug. Most other connectors use the same name but with female/male parts, such as SMA, BNC and N.
