1.RF connector overview
As an important microwave signal connecting component, the RF connector plays an important role in various electronic equipment, instruments, and wireless communication systems. After decades of development, RF coaxial connectors have formed an independent and complete professional system and have become an important part of the connector family. The rapid development of the information industry has effectively driven the continuous growth of the RF connector market. The SMA connector series is an important part of the RF connector family. SMA RF connectors are widely used in wireless base stations, telecommunications, microwave systems, instruments, handheld wireless devices, antennas, WiFi, etc. It can be said that it is the RF connector with the largest amount and the widest range of use.
2. Introduction to SMA.
(Subminiature Version A) The SMA connector is a precision coaxial connector (also known as an RF connector). It is named after the abbreviation of the English name. It is the smallest connector developed in the 1960s. It adopts a thread coupling mechanism and can be interconnected with 2.92mm and 3.5mm RF connectors. The thread standard of a 2.4mm RF connector is M7.0 x.75-6g, so it cannot be interconnected. The thread standard for the female head is 1/4-36uns-2A, and the thread standard for the male screw sleeve is 1/4-36uns-2B. The SMA RF connector has many advantages, such as being lightweight, miniaturization, anti-vibration, suitable for harsh environments, and so on.
The main parameters of SMA are:
Characteristic impedance: 50 Ω (the closer to 50 Ω, the lower the VSWR).
Frequency range: DC-18GHz
Rated voltage: 335V
Dielectric withstand voltage: 1000V
VSWR standing wave ratio (return loss): typical value (connected to RG174 cable): 1.15 +. 03 f (GHz) dc-12.4 GHz (the smaller the value, the lower the signal loss)
Insertion loss: max. 0.06 √ (f (GHz)) DB
Insulation resistance: 5000 m Ω minimum
RF leakage: max. - 60 dB (DC - 3 GHz)
Power: 72W@10GHz @25ºC
Operating temperature: - 65 ° C to + 165 ° C
Plugging times: 500 times
Coupling torque: 0.3 - 0.6 N-M
If you wish to know more about SMA connector ,click here.
3. Test results of the ultra-low price SMA connector
As we all know, competition in all industries has entered a mad stage in China, especially in the electronic industry, which has fast renewal, a short life cycle, the continuous breakthrough of technical barriers, large demand for products, and customers' demand for price reduction every year.
The inner volume of the electronic industry can be said to be the benchmark of various industries. Recently, an ultra-low price SMA female straight PCB connector (industry common code: SMA KE) has appeared on the market. A customer asked to buy this connector with a target price of 0.50 RMB (0.075 USD) and a quantity of 1000. This is indeed a shocking price. The usual selling price in the industry is 1.50–5.80 RMB (0.22-0.86 USD). The price will fluctuate according to the frequency range and gold plating requirements.
The international sales price of Mouser and DigiKey is between 3.5 and 4.0 USD (22-26 RMB). Based on the principle that there is no right to speak without investigation, 10 PCS products were purchased from an online shop in China for a complete evaluation. Existence is reasonable, Whether a 0.50rmb product can be used or not, it will produce those quality risks. We conducted a complete evaluation.
Do you interest what material is made of SMA connector? Check this link.
3.1 Dimensions
The body and insulator dimensions meet the general accuracy requirements and are within +/- 0.02 mm tolerance.
The body and inner contact are made of recycled brass, and the industry's minimum requirement is that the inner contact should be phosphor copper, and the standard is beryllium copper.
After multiple plugging, the elasticity between the pin and the jack will be reduced, the contact resistance will be increased, and the electrical performance will be reduced.
Recycled polytetrafluoroethylene (PTFE) is used as the insulator. There are many impurities, which will also affect the electrical properties.
The size of the inner contact is out of tolerance, the barb of the inner contact lacks edges and corners, and the inner contact cannot be fixed, resulting in the axial movement of the inner contact in the insulator.
3.2 Roughness
The surface roughness of the body and inner contact is relatively poor, and the shell is not beautiful enough.
Because the transmission of the high-frequency signal is a skin effect, the poor surface roughness of the inner conductor will lead to a serious decline in the performance at high frequencies.
3.3 Mate cycles
The number of plugging and unplugging has only reached 50 times, which cannot meet the standard requirement of 500 times.
3.4 VSWR (Return loss)
This VSWR is one of the most important indicators of an RF connector, but this connector has a very poor VSWR.
It is very easy to squeeze out the contact when it is installed on the PCB.
Once extruded, the inner contact exceeds the plane of the insulator, which directly destroys the interface size standard of SMA connector, and the VSWR will decrease linearly.
This type of connector is PCB in-line. Once the customer is welded and fixed, it is very troublesome to repair, virtually increasing labor costs.
3.5 Withstand voltage
1000V pass
3.6 Salt spray test
Unable to pass the 48-hour salt spray test, it is suspected that imitation gold is used. This coating looks like real gold to the naked eye. It's a kind of copper plating.
The anti-salt fog performance is very poor, and the end-user will soon turn yellow and black after use.
For real gold plating that can pass the 48-hour salt spray test, the plating cost of a body is more than 0.50RMB.
3.7 Insulation impedance
Pass.
3.8 GO/NO GO gauge
Pass.
4. Conclusion
The design of this connector is very mature, which can be said to be more than 60 years old. If they are produced according to IEC standards or national standards, the quality must be guaranteed.
It can be said that the RF connector is made into an ordinary wiring terminal electrical connector. They are all called connectors, but the performance requirements are very different.
Usually, SMA Jack Straight for PCB(SMA KE) is installed on the circuit board and connected with the antenna. Such an ultra-low price RF connector has great potential quality risk. It will lead to the rise of contact resistance and fire, poor signal, unstable signal transmission, and other quality problems.
