DIPOL Weekly Review – TV and SAT TV, CCTV, WLAN

400G transmission over 2400 kilometers.

The IEEE 802.3bs-2017 standard describing the capabilities of 400 Gbpss Ethernet data transmission over fiber has been a dominant topic at operator industry meetings around the world for about 2 years. At the Optical Fiber Communication Conference and Exhibition (OFC) 2023 held in San Diego in early March, the global provider of innovative network solutions Infinera reported a record-breaking 400 Gbps transmission distance of 2,400 kilometers using the Corning's TXF fiber. The transmission range achieved in this attempt is double the previous record. It is worth mentioning that TXF fibers are compliant with the IUT-T G.654E standard. What makes them different from "ordinary", popular single-mode fibers is the cutoff wavelength of 1520 nm (this means that these fibers can only be used for transmission in the 3rd or higher transmission window - wavelengths of 1550 nm and 1625 nm) and a much larger diameter of the modulus field (i.e. the effective area of light propagation in the fiber), which here is 12.4 μm, instead of 9 μm in standard fibers.

Cisco and Sipartech are proud of a very similar achievement. During the tests, transmission over a distance of more than 1,337 km was performed. In this case, the long-distance fiber route led from Paris to Clermont-Ferrand, then to Lyon and back to Paris using mixed fibers.

DD 2400 meter for RF measurements – one connector for different signal sources.

In addition to the measurement of individual parameters of digital TV signals, which have a significant impact on the correct implementation and operation of RF/SAT systems, one of the main criteria in selecting a meter is the ease of use and functionality. Certainly, a much more convenient device will be a meter that has one input common for DVB-T2 and DVB-S/S2 signals. This solution eliminates the cumbersome switching or rearranging of the measurement cable when measuring directly from the multiswitch. Another important feature is the measurement of RF signals over a very wide range, which eliminates the problem of signal overdriving on individual elements in the system as well as the meter itself.

Is it worth using fiber optic meters with an OTDR function?

Due to the ever-increasing popularity of fiber optics, the issue of being able to take proper measurements for an optical path is becoming important. Installers often decide to buy the cheapest OTDRs or meters with an OTDR function thinking that they will allow them to perform measurements in a quick and hassle-free manner, and, in case of problems, make a full diagnostics of the link.

However, the truth is sometimes painful, and it turns out that in this case "cheap" can be the enemy of "good", but, of course, this is not the rule. However, it is worth knowing that the purchase of the cheapest devices of this type is generally decided by people who do not have practical experience and the required minimum theoretical knowledge. Practice shows that cheaper OTDRs, due to their limited capabilities in presenting results, require more knowledge from the user to interpret them skillfully or to understand why certain information simply cannot be obtained.

The following is an example of a measurement using a cheap OTDR, or rather a meter with an OTDR function, since at first glance you can see that this device does not measure reflectance, which is what it has been really designed for and its function is based on.

The above reflectogram perfectly shows reflectance (reflective) events – most often these are the connectors. In the table, the column where the values of this parameter for individual events should be is empty. Thus, the installer has no information on the actual quality of the connections made – such a connector should have low attenuation and reflect as little light as possible. So if the measurement order includes a demonstration of the correct reflectance for the connector standard, this device will be useless. Furthermore, as mentioned earlier, the lack of information about the reflectance value severely limits the diagnostic possibilities. In the example described, two connectors are involved - event #5 and #6. The first one attenuates slightly more than 0.5 dB, the second slightly more than 0.9 dB. Both consist of 2 splices and a connector. Thus, in the case of the second connector, the measured attenuation is greater than typically expected (2x 0.1 dB + (0.3...0.5) dB = 0.5...0.7 dB). Without reflectance information, you do not know whether the increased attenuation is derived from inferior splices or a weaker disconnected connection. In the case of reflectance information, if it was normal, the fault would most likely lie in the splices, in the case of low reflectance the connector would be to blame.

In the example in question, a 50m run-up fiber is used. The pulse width has been set to 50 ns, which is generally appropriate for measurements of sections of several kilometers in length – in this example it is about 4.3 km. In the screenshots above, it can be seen that despite the use of 50 m of fiber to eliminate the dead zone, the zone extends to the second event, preventing proper measurement of the attenuation of the first connector in the system. The attenuation measured is 0.88 dB, but since the curve on the graph did not reach the correct level before the connector, this measurement is distorted to the detriment of the installer (the attenuation is overestimated). The size of the dead zone depends on the width of the measurement pulse (here 50 ns), but also on the quality of the electronics and components used to build the device – the cheapest ones will be clearly inferior in this regard, generating larger dead zones at the beginning of the measured path and after any reflectance event.

A solution to this problem (in addition to using higher-end devices and taking care of the cleanliness of the measurement connector) is to use a longer run-up fiber or reduce the measurement pulse. A smaller measurement pulse means, by definition, smaller dead zones. Unfortunately, in this particular case, a clear spike in the noise of the graph can be seen already for a pulse of 50 ns after event #5 at 2958 meter and subsequent events. Such noise negatively affects the accuracy of the measurement and prevents proper recognition of events by the OTDR. The presence of noise means that the pulse used (50 ns) is too weak and it would be advisable to use a wider pulse (this will smooth out the graph). This, in turn, will negatively affect the size of the dead zones and the circle closes.

The last issue is the ability of the device to recognize events. There is no denying that with this it can vary even with the most expensive equipment. However, it is worth looking at the example in question. In the following enlarged excerpt from the graph, you can clearly see the drop in the level of the backscattered signal. This is a splice with an attenuation of about 0.21 dB, determined manually with markers after the measurement itself. This event has been completely ignored by the device and not listed in the event list in the table. An informed user will search for this event, measure its properties manually and include it in the measurement report. A user without the basic knowledge may have a problem with this.

So are the cheapest devices with and OTDR function useless? Absolutely not. The example described – despite the fact that the measurement has not been quite correctly performed (it would be necessary to use a larger run-up fiber and a wider pulse) – delivers a lot of information about the optical path. You can see the length of the fiber, you can locate most of the events and measure some of them. So, it is a good tool for finding faults (and, depending on the situation, their causes) in the network – broken fibers, bad connectors, etc. More detailed diagnostics can be performed, but with the knowledge of the limitations described above. For full-fledged measurements, however, it is recommended to use equipment that can measure and record the value of reflectance - for example, the Grandway FHO3000 L5828 OTDR.

Diagram of video door entry system for one-family house with an additional IP camera.

When building a modern video intercom system you need to take into account that the video intercom can control the gate and entrance. An application installed on a smartphone can be used for this purpose. When installing a door station, the view from the built-in camera focuses on the caller. If the camera has a very wide viewing angle, it is possible to observe the area in front of the gate, but even if the door station covers such an area, it is usually insufficient.

An additional IP camera can be connected to the Hikvision IP video intercom system to cover the area of the entrance gate or the entrance gate and wicket. During or after answering the call, you can change the view from the main gate station to the additional IP camera and view the area in front of the gate. Thanks to remote operation via a smartphone, it is possible to open and verify remotely at any time, whether the entrance gate is open or closed.

The diagram of an IP video intercom system for a single-family house is shown below. The system is based on the one-subscriber IP Villa DS-KV8113-WME1(B) G73639 door station with a built-in camera and two relays for control of the gate and wicket. The DS-KH6320-WTE1 G74001 monitor equipped with Wi-Fi interface has been installed inside the building. The area at the gate can be viewed with the Hikvision DS-2CD1023G0E-I(C) K17662 IP camera. The Ultipower N299781 switch with 4 PoE ports (802.3af/at) is used to power the gateway station, monitor, and IP camera. The system is connected to the Internet via the Mercusys AC12G N2933 router. The wicket is controlled with the use of the Bira S12U G74220 electric door strike with steel keeper/latch with 4 mm adjustment range, suitable for 12 V AC or DC power supply. It is supplied with the 12 V DC M1820 power supply.

Popular GSM antenna.

The Yagi-Uda or Yagi antenna is one of the most popular antenna designs. Despite a relatively simple design, it has a high gain, typically greater than 10 dBi. Such antennas can operate in the HF to UHF bands (3 MHz to 3 GHz), but often within a limited bandwidth around the center frequency of the Yagi antenna.

The concept of Yagi-Uda antenna was invented in Japan by Shintaro Uda in 1926 and published in Japanese. The work was presented for the first time in English by professor Yagi who went to America and greatly contributed to widespread use of the design.

The basic geometry of a Yagi antenna is shown in the diagram below. The antenna has only a single active (driven) element, typically a half wave dipole or folded dipole. It means that only this member (W) of the structure is excited (fed/driven via a feed line from a generator). The rest of the components are parasitic elements which help to transmit the energy in a particular direction. The dipole is almost always the second element from the end, with a length to make it resonant at the center frequency (the required length of the dipole is somewhere between 0.45 and 0.48 of the wavelength).

The element located behind the vibrator (figure above) is the reflector (R). Its length is slightly longer than that of the vibrator. Usually one reflector is used, since increasing their number does not significantly improve antenna parameters. The reflector lowers the relative level of the back lobe of the antenna's radiation pattern, thus reducing the amount of power radiated in the opposite direction while increasing the antenna's gain. The increased length of the reflector relative to the vibrator provides two benefits. First, the longer element provides more effective wave reflection, increasing the antenna gain. Furthermore, if the reflector is longer than the vibrator being in resonance, the impedance of the reflector is inductive (the voltage along the reflector precedes the current in phase).

The GSM ATK 10 800-980 A7025 MHz antenna is a 10-element directional outdoor antenna designed to transmit mobile telephony signals. The antenna features up to 12.8 dBi gain for frequencies from 800 to 970 MHz, making it ideal for connecting to Internet modems. The antenna is shorted for direct current.

Remote PoE switch power supply. The ULTIPOWER 352SFP N299707 PoE switch has the Powered Device function that allows it to be powered by connecting to another PoE switch. This function is particularly handy when only one twisted-pair cable is connected to the switch installation site (and the cameras, if installed in the same place, e.g. on a pole)...>>>more