SMA Connector
SMA stands for SubMinature version A and was developed the 1960's when smaller RF connectors were needed for space and higher density airborne applications. The SMA's typically are 50 Ohm and will not mate to the F connector found on most cable TV hookups. F connectors and SMA look very similar. SMA's can go to 26.5 GHz (depending on the manufacturer) and are commonly built of two base metals, brass and stainless steel. Both base metals can be plated with gold and only brass is plated with nickel. Stainless steel SMAs will typically go to 26.5 GHz and brass will be much lower in frequency typically 12 GHz - Depending on Manufacturer. The base design of the connector is on MIL-39012. QPL (Qualified Parts List) connectors are available. The SMA male uses a hex nut that is 5/16 inch (0.313 or 7.9mm). There are 36 thread per inch in the barrel.
Advantages to the SMA
It is very common, relativity inexpensive and robust. You can get an SMA for a large cable such as an RG-214, LMR-400 which has a 0.4 inch (10.1mm) OD or as small as 0.034 inch (0.86mm). This cable which is not much bigger that human hair.
The SMA is robust, and it very difficult to break.The SMA has good EMI characteristics. The solder on version will only leak near the gap where the nut rotates 95-105 dB are very common with the SMA for shielding. The SMA is very stable once it is screwed on, it stays there.
Disadvantages to SMA
Larger than either the SMB or SMC. More expensive than the SMB.
Why us a QPL:
The short answer is you know what your are getting. The QPL parts are of higher quality, the threads are better, the material is cut crisper, and the performance is consistent. The manufactures that have QPL lines do produce better standard products. This does not come without a cost which is a higher price.
Variants- SSMA
The connector is a miniature version of the SMA. It is about 1/2 the size.
SMB Connector
SMB stands for SubMiniature Version B. It was also developed in the 1960's The goal of this connector is a quick connect and disconnect at a low cost. This connector is commonly used in commercial systems where a field replaceable module exists and it needs to be snapped in. The connector is a good reliable connector to 4 GHz. The connector is low cost. The base material is brass and comes with nickel or gold plating. Though some QPL parts are available.
Advantages to SMB
The SMB does have advantages. The SMB is a robust and reliable push-on connector. Further, the SMB is lower in cost than the SMA or the SMC. The SMB offers a option that is a true 75 Ohm version. The SMB is manufactured by many manufactures and is very stable and available. SMB's will be here for a long time. If you have the space on the board for the SMB it is an excellent choice. There are many PC board mount options available. It is available for the cables RG-316, RG-174, RG-178, LMR-100, RG-58, RG-400, RG-142.
Disadvantages to the SMB
Can pop off unlike the SMC and SMA. The frequency performance is not as good as other snap-on connectors such as the SMP. The drawback is the connector is not as popular with customers: The reasons are: Its size is almost as big as an SMA and the electrical performance is only to 4 GHz. For higher frequencies applications the SMPs are looking more attractive. For lower frequency and size limitations the proprietary push-on such as U.FL, OSMT, MC card are becoming more common. The SMB does have advantages over the fore-mentioned connectors. The SMB is much lower cost than SMP's. The SMB is generic so you are not tied to a single manufacturer in the event they discontinue manufacturing your part. We expect to see the SMB for a long time.
Variants- SSMB
The connector is a miniature version of the SMB. It is about 1/2 the size.
SMC Connector
SMC stands for SubMininature version C. This was also developed in the 1960's and is a hybrid of the SMA and the SMB. The nut uses 10-32 UNF threaded interface and looks similar to the SMA. The SMC and SMA are not compatible and will not plug in. Typical SMC's are usable past 10 GHz. The plug which looks like a SMA male has a female contact. The SMC is very similar to the SMB both have the same pin size and dielectric interface. The major difference is the the SMC as a threads and the SMB is a push-on.
Advantages of the SMC
It is a screw-on connectors unlike the SMB. It has a wider frequency response than the SMB. It is smaller than the SMA. Connectors are available for most cable types. The SMC is lower cost than the SMP. More durable than smaller connectors such as MCX, MMCX, SMP. The advantage over the SMA is a different interface. If you have a row of SMA's you can put a SMC and not accidentally plug it in.
Disadvantage of the SMC
Not widely adopted connector. Typically more expensive than the SMB and about the same or higher than the SMA. Lower frequency response than the SMA. Larger than the MCX, MMCX and SMP.
Variants- SSMC
The connector is a miniature version of the SMC. It is about 1/2 the size. This version is used by Aerospace companies because of it's small size and safety of having the connector screw-on. Very high quality versions are available for aerospace applications.
Who make the best connectors?
The short answer is they all do. It depends more on what you want to do with the connector. Example some manufactures make an excellent low frequency SMA which is low cost. For users in the 2 GHz it is excellent, but at 10 GHz it looks more like a door knob. Other manufactures make a excellent stainless steel SMA that goes to 26.5 GHz, but more expensive, but reasonable considering what it does.
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