Sunday, April 27, 2014

Various kinds network cable

Network cable can be classified into coaxial cable, twisted pair, and optical fiber cable. 

1,Coaxial cable: it’s a kind cable with core copper wire shielded  by insulative layer, which have a capacity
of tough disturbance resisting, stable data transmitting, low price; and I must mention this kind cable also been used for closed circuit TV. The coaxial cable should be used together with BNC Connector, but customer can ask the factory supply cable assembly which the BNC connector already connected with the raw cable wire.

2, Optical fiber cable: it’s the fastest cable been used today, but its price are high, very rare been used in household places. It’s a kind cable consisted of hair-like glass fiber shielded with insulation layer. Rely on optical pulses to transmit data, Optical fiber cable have an extremely strong resistance to interference, high security for data transmission, high speed, large data transmitting capacity. Below, I will introduce the difference between single-mode optical fiber and Multi-mode optical fiber.

(1Multimode optical fiber.

In multimode optical fiber, the data are transmitted through more than one route, it often been used within a mile’s distance, as the effective distance from transmitter to receiver is about 5miles; furthermore, stronger the source light, more sensitive the receiver, larger distance will be achieved. Our research tells the bandwidth of multimode optical fiber is about 4000Mb/s; single mode optical fiber is used to avoid pulse broadening, the minimum size of fiber core (7-9μ) avoided the jump pulse from side to side. When we use a confocal laser in a wavelength of 1310 and 1550, we see the laser going directly into the tiny fiber core and to be transmitted to the receiver without apparent jumping.

2single-mode optical fiber
Single-mode optical fiber have a thinner fiber core, the optical pulses can be transmitted directly to the center of the core. Single-mode optical fiber often been utilized in a longer distance. The signal lost by single-mode optical fiber is lower than a multi-mode optical fiber, for example, in a distance of 3000 feet, multi-mode optical fiber would lose 50% of its signal strength, but for single-mode optical fiber, only 6.25%.The potentiality of Single-mode optical fiber made the only choice for us to employ it in long distance and high speed data transmission. Our recent test point out, a 40G 64 Ethernet information channel can be transmitted as long as 2840 miles. In safe application, the common determining factor for us whether to choose single-mode optical fiber or multi-mode optical fiber is distance: longer distance above 5 miles normally made a choice of single-mode optical fiber; multi-mode optical fiber is used within a 5miles distance, however, the bandwidth should not ignored, we should choose single-mode optical fiber if the future transmission include large bandwidth signals.

3. twisted pair:
Twisted pair is two cable wires stranded together, the standing can make electromagnetic waves neutralized between two wires, can resist outside electromagnetic interference. Twisted pair has a limited transmitting distance, information channel width, and transmitting speed comparing with other transmitting medium, but have a relatively lower price.

The most commonly used twisted pair cables are: CAT3, CAT5, CAT5E and CAT6, the former have thinner diameter, while the later have thicker diameter.

(1)   CAT1, this is a kind cable mainly used to transmit sounds, not for transmit data. The standard of Cat1 is mainly used for telephone in the beginning of eighties.

(2)CAT2, The frequency for this type is 1MHZ, used for sound transmitting and transmitting a low data not more than 4Mbps.The application of CAT2 commonly seen in 4Mbps token passing protocols based old token-ring network

(3)CAT3,This is a kind prescribed cable used in ANSI and EIA/TIA568 protocol, having a transmitting frequency of 16MHz,CAT3 are used for sound transmitting and 10Mbps data transmitting and below. Mainly used for 10BASE—T.

(4)CAT4, with a transmitting frequency of 20MHz, this kind cable mainly used for sound transmitting and data transmitting in 16Mbps and below, used mainly in Token Ring based local area network (LAN) and 10BASE-T.

(5)CAT5, this kind wire increased winding thickness, clad with a kinds of high quality insulation material, Cat5 have a transmitting rate of 100MHz, used for sound transmitting and data transmitting in 100Mbps and below. Cat5 is the most commonly used Ethernet cable for 100BASE-T and 10BASE-T internet.

(6)CAT5E, it’s a kind cable with low attenuation and lesser crosstalk, a higher attenuation to crosstalk ratio
and higher Signal-to-noise ratio, low time-delay errors, greatly improved the performance. CAT5E is mainly used for billibit Ethernet (1000Mbps)
PS:the higher the attenuation to crosstalk ratio (ACR) for a given cable, the less chance of signal errors, the higher the Signal-to-noise ration means less distortion.

(7)CAT6, with a transmit frequency of 1MHz-250MHz, cat6 wiring system should have a relative larger margin for general attenuation-to-crosstalk ratio in 200MHz,it provides 2 times bandwidth than CAT5E. The transmitting performance of CAT6 is high above the standard of CAT5E, which made it most suitably for a application with a transmitting rate above 1Gbps.A big difference for CAT6 comparing with Cat5e is the improvement on the aspect of crosstalk and return loss; cat6 canceled the basic link model but adopted star-shaped topological structure, requesting the cabling distance of a permanent link within 90m and information channel length within 100m.

(8)CAT6E, This is an updated version of cat6, belongs to a kind of Unshielded Twisted Pair (UTP) under the standard of ANSI/EIA/TIA-568B.2 and ISO 6/E, mainly used in Gigabit Ethernet.CAT6E have the same transmitting frequency with CAT6, i.e. 200-250MHZ, the largest transmitting speed of CAT6E is 1000Mbps.Comparing with CAT6, CAT6E greatly bettered the aspects in crosstalk, attenuation, and signal-to-noise ratio (SNR).

(9)CAT7, this is an updated twisted pair under the standard of ISO7/F, mainly for the application and development of 10 Gigabit Ethernet. But, it no longer belongs to a kind of unshielded twisted pair (UTP), but kind of shielded twisted pair (STP).CAT7 has a transmitting frequency above 500MHz, 2 times than CAT6 and CAT6E, and 10Gbps’transmittiong rate.

PS: STP is shielded with aluminum foil, it can reduce radiation, but cannot completely remove it, STP have a higher price than UTP, and installation will not be so easy as UTP, mostly we suggest customers buy UTP for it have advantages such as: Saving space for its smaller diameter, lesser weight, easy bent, easy installation, reduced the crosstalk to the minimum, fire resistance, independent and flexible, suitable for structured and integrated wiring.

Wednesday, April 23, 2014

S-VHS cable

When we talking about S-VHS cable, we need to know the S-VHS, so what S-VHS is? I would like to give you a general account of S-VHS below:

S-VHS is short for super video home system; this is a new model developed by JVCKENWOOD Corporation (Abbreviation: JVC) in succeeding of VHS by other companies, the new model have a characteristic of high resolution, high fidelity, 20Hz-20KHz’bandwidth, 90dB above dynamic and signal-to-noise ratio. On a par with LD’s image and CD’S sound, S-VHS becomes indispensable equipment for all the Hi-Vi Lovers.

S-VHS have an inferior image quality than DVD’s, but 500TVL’s resolution for most TV can’t achieve, and also you can hardly judge the image quality difference with our naked eye either it played in S-VHS or DVD. Furthermore, the forward compatibility means all VHS tapes can be played in S-VHS player, but it’s not the other way around.
Developed on the basis of VHS, S-VHS greatly improved the performance for the compatibility with VHS, and below ,I need to lay the details concerning the electronic circuit, magnetic heads, tapes  which have a thoroughly improvement.
1,The videos Y signal for S-VHS expanded upwardly to the phase of 7MHz, frequency deviation improved to 1.6MHZ,effective bandwidth for brightness improved to 5MHz comparing with VHS’s 1.0MHz and 3.2MHz.According a general calculation for resolution that 1MHzs bandwidth equals 80TVL, we can know that VHSs resolution is about 250TVL,S-VHS reached to 400TVL above. That’s huge improvement for image quality.

2, after the improvement of bandwidth, the crystalline magnetic head is no long adapt to eddy current loss and the clutter interference by high frequency, so JVC redeveloped amorphous magnetic heads which was laminated by several thin-films to improve insulation and reduce eddy current. Quite effectively improved highlow frequency performance, and bettered the chroma frequency signal in the lower end of the spectrum, which greatly improved the color saturation.

3, In order to reduce interference between brightness (Y) signal and color (C) signal, S-VHS video recorder handling Y/C signal separately on recording and playing, placing the Y and C signal in a better functioning  condition.
4,To adapt the needs of high sensitivity of new magnetic head of broadband, using chromium and Iron oxide Fe2O3 for high magnetic saturated coating with a thickness of only 0.5μm ,greatly improved thermoremanent  magnetizationTRMand coercive force, in this way, the signal recording improved.
5, during the process of signal transaction, time-constant is utilized to limit amplitude and impose accentuation, which, in a way, greatly reduced the edge noise of image. The noise in the nonlinear region is also repressed by synchronizing time-constant with inputted signal level.

6,With an audio frequency response of 12 KHz, its not enough for VHS recording a high fidelity program. 33.35mm/s’ tape speed, relatively lower than cassette tapes 47.6mm/s; Improving the tape speed is the only way to improve frequency response. Introducing the specialized Hi-Fi sound accompaniment magnetic head in the high speed rotary drum can make magnetic heads relative tape speed running 5.8m/s, which is 170 times higher than static sound accompaniment magnetic head, can achieve 20KHz’ frequency response recorded by rotary magnetic head, if the recording in EP Mode(1/3s normal speed-slow speed), still  a record of 20KHz  maintained ,which makes high fidelity sound accompaniment come true.
7, Based on different characteristics of S-VHS sound accompaniment frequency modulation and whiteness’s frequency modulation. Deep oriented recording method adopted to record the accompaniment sound signal in a blank tape before recording the image signal on the surface, improved the accompaniment standard and efficiently used the tape.

Now, let’s come back to S-VHS cable, while running S-VHS machines properly, a cable connecting between devices is necessary. A brief and simple definition for S-VHS cable is a kind of wire connecting S-VHS devices. Anyway, you can easily know S-VHS cable after you know what S-VHS is. Good quality cables can guarantee S-VHS’s sound and image quality; make S-VHS’s advantage prominent. So don’t lose your S-VHS’s advantage by choosing a good quality cable can be never ignored while you buy the machine but the cable separately.

Friday, April 18, 2014

IEEE 1394

IEEE1394 interface was developed by Apple Inc. Same as USB, IEEE1394 can support peripheral hot swapping and providing power, connecting several difference devices and support synchronous data transmission.
Backplane mode and cable mode are two modes IEEE1394 used for data transmission.Backplane mode can be classified into 12.5 Mbps 25 Mbps50 Mbps ,the lowest rate is higher than USB1.1;Cable mode can be classified into several kinds such as 100Mbps, 200Mbps and 400Mbps; its the mode of high speed, can transmit uncompressed?high quality data for film.1394b is an updated version of 1394, its the only and specialized home network standard designed for audio, video, control and computer. It realized high performance home network through low cost, safety cat5. Long before the time of USB1.1, 1394a interface had possessed a great advantage for its higher speed, but after the coming out of USB2.0, 1394a interface did not possess a very apparent advantage. Meanwhile, many mainstream computers did not have a 1394 interface, if need to be used, relative connector should be used, which would undoubtedly increase the cost. External optical storages with unitary 1394 interface are basically few, mostly are with 1394 and USB together, the usage is more convenient.

The original design of IEEE1394 can allow user edit digital media archive directly thorough IEEE1394 interface to save the space of hard disk by using a computer. Before the coming out of IEEE1394, a special hardware should be used to edit digital media by downloading the film in a hard disk. As the trending of lower price for hard disk space, high speed IEEE1394 replaced USB2.0 to become the best interface for computer hard disk oppositely.Theoretically, 1394a can support the longest wire length 4.5m, have a standard transmitting rate of 100Mbps, and can support more than 63 devices.IEEE1394 has three protocol layers: transaction layer, Physical layer, Data link layer. Among them, transaction layer only support asynchronous transfer, synchronous transfer is provided by data link layer.
IEEE1394 inherited a mature SCSI instructional system and have a stable and efficient transmitting rate. Comparing with USB2.0, CPU has a lighter burden; even though IEEE1394a have a account value lower than USB2.0, the actual transmitting rate is higher than USB2.0,so it used widely for the high speed and stable data transmitting.

How to know if a buyer is a scammer or not?

1, he does not have any clear requirements regarding product quantity or specification. For example, he only asks price or wants you to send...