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

A new standard for optical networks.

IEEE, the world's largest organization of electronic and electrical engineers, has published the IEEE 802.3cc-2017 standard, which, for the first time, defines the principles of the construction of Ethernet fiber networks operating at 25 Gbps via single single-mode fibers over lengths up to 10 km and 40 km. The standard is addressed to metropolitan networks and large data centers and companies whose core networks operate at 100 Gbps, with requirements for efficient branches.

The standard enables operators to cheaply modernize existing systems preserving the current network architecture, as well as management and software tools. It is an example of how quickly standards can be adapted to industry requirements for a steady increase in network bandwidth.

In order to meet the requirements of adapting network capacity to the growing demands, the IEEE Standards Association issues updates for both wireless and for cable networks based on twisted-pair cables and optical fibers as the transmission medium. The IEEE-SA has developed over 1,200 active standards, and more than 650 are in the development phase.

Sharp images in CCTV systems - depth of field.

To draw the attention of the viewers, photographers and cinematographers often use small DOF, also called shallow focus. In contrast, users of CCTV systems demand sharp images of the whole monitored scenes, so a large DOF is a must.

Depth of field determines the distance between the nearest and farthest objects in a scene that appear acceptably sharp in the image. Assuming that we use a lens with appropriate parameters (i.e. its resolution is harmonized with the resolution of the camera in the whole field of view), the depth of field can be calculated using the formula:

where:
DOF – depth of field [mm]
N – F-number of the lens opening (iris)
f – focal length of the lens [mm]
s – the distance at which the lens is focused [mm]
c – the circle of confusion for a given image format, it can be assumed 0.005 mm for 1/3" image sensor

According to the formula given above, the depth of field depends on:

• the distance at which the lens is focused (the distance between the "sharpest" object and the lens) – the shorter distance the smaller depth of field (quadratic dependence),
• iris diaphragm – the higher value the smaller the opening (aperture) through which the light enters and the greater the depth of field is (linear dependence),
• focal length - the longer the smaller the depth of field (quadratic dependence).

To summarize: in order to get the entire image sharp, the installer should use a high diaphragm (small aperture) and lens with the shortest possible focal length. So, if the field of view is too wide, the camera should be located closer to the observed object(s). If the small aperture results in a dark image, it is better to use a camera with a more sensitive image sensor, or switch it to B/W mode, where applicable.

Channel conversion in MATV systems.

Over years, vital parameters of coaxial cables, especially of those with low quality, are continually worsening. It is manifested by increased attenuation, lower screening efficiency and return loss. These effects are more significant in the higher frequency range, where the attenuation of coaxial cables grows. This creates a risk that digital channels can be pixelated or frozen.

The use of channel converters allows for moving DVB-T multiplexes to other, lower channels. This can eliminate the problems associated with too high attenuation of the old cables at high channels. Advanced channel converters can also stabilize the level of the output signal, regardless of the fluctuations of the input signal (within the rated range).

The device can operate in two modes:

• transparent mode - the decoded transport stream is not modified and is directly applied to the COFDM modulator without PID filtration,
• multiplexing mode - the device examines the decoded transport stream (measures the bit rate, updates SI arrays) and optionally filters programs and services.

Superior selectivity of the ttx-420 R81616 module is guaranteed by the application of SAW filters. MER (modulation error rate) at the output of the device is not lower than 38 dB (100-780 MHz) or 35 dB (780-860 MHz), and the maximum output level is 90 dBμV.

Support for corridor mode in iVMS-4200 app.

Hikvision cameras have "Rotate Mode" which is particularly useful for observing areas such as corridors or hallways, characterized by a large disparity in size between the depth (visible by a camera as the height) and width of the scene. In this mode, one camera is capable of capturing a "deep" or "vertically-shaped" scene from a comparatively short distance, cutting out the inessential information from the both sides in the immediate vicinity of the camera. In order to display the image properly via iVMS-4200 application, it is necessary to enter Tools->System Configuration->Image submenu and, in the View Scale, set the Original Resolution option. Simply, a camera that normally provides video with 16:9 aspect ratio, in corridor mode switches the ratio to 9:16, so it is necessary to keep this parameter in the application.

System Configuration window in iVMS-4200 client software

WiFi network in a small school.

Wireless network in a small school differs from similar installations in larger facilities mainly in the number of access points necessary for proper coverage of the whole school building. The best practice for this type of wireless network is also to create several completely independent SSIDs (Service Set Identifiers), so that individual user groups connect to their specific WiFi networks (separate for students, teachers, administrative staff, guests after classes).

I - students' devices, II - teachers' devices
Example architecture of a school WiFi network based on TP-Link network devices

The most important thing is that the wireless networks are to be isolated - devices connected to one network cannot be visible to devices in other networks. EAP access points can be highly recommended for creating reliable and efficient Wi-Fi networks in the demanding school environments. The modern devices can be easily mounted to walls or ceilings. EAP Controller Software enables centralized configuration and management of the wireless network composed of multiple EAP devices. The functions include real-time monitoring, graphical analysis of the network traffic and batch firmware updates.

Wireless Access Point TP-Link EAP225 (dual-band, 802.3ac, PoE 802.3af) N2567

Optical links - transmission via one or two fibers?

When deploying fiber optic installations, installers often decide to lay cables with redundant fibers. This is mainly due to a small difference in price and the desire to have spare fibers for future use.

A pair of SFP modules implementing WDM technology enabling two-way transmission via a single fiber uses two wavelengths. One of the devices transmits optical signal in the III transmission window (1550 nm) and receives different signal from the second device using the II transmission window (1310 nm), the second one uses the complementary wavelengths. So, the modules have to be properly paired e.g. L1416 and L1417, otherwise the link will not work.

In the case of a cable with spare fibers, the installer has the possibility to choose between the case described above and a solution using two fibers. The WDM devices (for the transmissions via single fibers) are only a little bit more expensive than duplex devices used with pairs of fibers. The higher cost can often be compensated by savings on the number of pigtails, patch cords, splices.

However, from the purely technical side, duplex connections seem to be slightly better due to the fact that they use only one wavelength (in the case of single mode connections it is 1310 nm in both directions). WDM connections use two wavelengths (most often 1310 nm and 1550 nm), so that all network measurements should be performed for the both wavelengths. It should be remembered that all events in the optical path, such as splices, micro- and macro-bending have different effects at different wavelengths. Thus, with the WDM connection, there may be a significant difference in signal attenuation between the directions (due to different wavelengths). In an extreme case, it is possible to have a one-way connection only. Duplex connections, due to the use of one, the same wavelength, are free of such problems.

Video monitoring of single-family home, based on H.265/H.265+ Signal IP cameras. The diagram below shows such a system based on 2 MP Signal IP cameras with H.265 video compression. The indoor HDV-200P K1817 and outdoor HDC-260P K1877 cameras are equipped with 2.8 - 12 mm varifocal lenses allowing for changing their viewing angles within 90° - 26° range. The built-in IR illuminators ensure good visibility even in complete darkness. All the cameras are connected to the system and powered via 8-port PoE switch ULTIPOWER N29982... >>>more

Video monitoring of a home, based on 2-megapixel Signal IP cameras

Signal Fire AI-8 fusion splicer