This is the Section 1 Module 8 of the compiled Communications Coaching Materials taken from various sources including but not limited to past Board Examination Questions in Electronic System and Technologies (EST), Communications Books, Journals and other Communications References. This particular Coaching Notes in Communications Engineering has random Questions and Answers in random topics. Make sure to familiarize each questions to increase the chance of passing the ECE Board Exam.
Communications Engineering Coaching: Section 1 Module 8
AM – 455 kHz
FM – 10.7 MHz
Radar – 30MHz
TV receiver – 36-46 MHz
North American sub band for CATV
T-7 5.75 – 11.75(MHz)
T-8 11.75 – 17.75
T-9 17.75 – 23.75
Until T-13 (just add 6Mhz)
-Russian counterpart of the USA’s GPS
-24 satellites (21 operating, 3 spare), 45 degrees separation
-3 orbital planes, 120 degrees separation
-64.8 degrees angle of inclination
-19100 km altitude
-11 hours and 15 minutes approximate orbit time
Universal Product Code (BARCODE) consists of:
-flag, for indicating the country, 2-3digits
-maker code, 5-7 digits
-item code, 5 or 3 digits
-Check digit, for preventing from errors, 1 digit
Group of faxes:
· Group 1 faxes conform to the ITU-T Recommendation T.2. Group 1 faxes take 6 minutes to transmit a single pace, with vertical resolution of 98 scan lines per inch. Group 1 fax machines are obsolete and no longer manufactured.
· Group 2 faxes conform to the ITU-T Recommendation T.30 and T.3. Group 2 faxes take 3 minutes to transmit a single page, with a vertical resolution of 100 scan lines per inch. Group 2 fax machines are almost obsolete and no longer manufactured. Group 2 fax machines can interoperate with Group 3 fax machines.
· Group 3 faxes conform to the ITU-T Recommendation T.30 and T.4. Group 3 fax machines take between 6 and 15 seconds to transmit a single pace (not including the initial time for the fax machines to handshake and synchronize). The horizontal and vertical resolutions are allowed by the T.4 standard to vary among a set of fixed resolutions:
- Horizontal: 100 scan lines per inch; Vertical 100 scan lines per inch
- H: 200 or 204 SL/inch; V: 100 or 98 SL/inch (‘standard’); V: 200 or 196 SL/inch (‘fine’); V: 400 or 391 SL/inch (‘super fine’)
- H: 300 SL/inch; V: 300 SL/inch
- H: 400 or 408 SL/inch; V: 400 or 391 SL/inch
· Group 4 faxes conform to the ITU-T Recommendations T.563, T.503, T.521, T.62, T.70, T.72, T.411 to T.417. They are designed to operate over 64kbit/s digital ISDN circuits. Their resolution is determined by the T.6 recommendation, which is a superset of the T.4 recommendation.
RFID (Radio Frequency Identification Systems) are intended to carry data in suitable transponders, generally known as tags, and to retrieve data, by hand- or machine- means, at a suitable time and place to satisfy particular application needs.
RFID (radio Frequency Identity) systems employ tiny chips and wireless antennas that can be imbedded into products and used for unique identification purposes. It is a contact-less solution that works with proximity readers and RFID tags.
Proximity readers – a device which transmits and interrogating/querying signal to an RFID tag and received unique information from the tag.
a) low power with ERP not exceeding 500mW
b) high power with ERP not exceeding 2W or 4W EIRP
RFID tag – a microchip attached to an antenna than picks up signals from and sends signals to a reader. A tag contains a unique number, but may have other information as customers’ account number
RFID tags maybe classified as:
a) active tag – used for long distance purposes such as in toll highways, parking areas, gas stations. This tag uses small batteries which enable it to send signals at a longer distance
b) passive tags – used very near or in close proximity to a reader and does not use any internal battery
The use and operation of RFIDs shall be allowed in the following frequency bands:
13.553 – 13.567 Mhz
918 – 920 Mhz
2446 – 2454 Mhz
Proximity readers shall be covered by a certificate of registration to be issued upon one-time payment of the following fees:
a. low power readers, PHP 100.00
b. high power readers, PHP 300.00
Imported RFID tags shall be covered by Permit to Import to be issued upon payment of Permit fee of PHP 100.00 per 1,000 units.
Sale of unregistered RFID proximity reader, PHP 5,000.00 per unit or with forfeiture of equipment
Selling of RFID tags not covered by Permit Fee, PHP 2,500.00 for the 1st offense, PHP 5,000.00 for the 2nd offense, PHP 7,500.00 for the 3rd and so on.
Illegal acquisition of RFID reader, PHP 5,000.00 per unit and/or with forfeiture of equipment.
Sale of illegally acquired RFID reader, PHP 5,000.00 per unit or with forfeiture of equipment.
Non-registration of imported RFID readers within five (5) days from release from the Bureau of Customs, PHP 1,000.00 per unit
Selling of RFID proximity readers by non-NTC accredited radio dealers/manufacturers, PHP 5,000.00 per reader, PHP 1,000.00 per 1,000 tags.
Operating RFID proximity reader without valid registration, PHP 5,000 per reader
|Specifications||Cable Type||Max Length (m)|
|10BaseT||Unshielded Twisted Pair||100|
|10Base2||Thin Coax Cable||180|
|10Base5||Thick Coax Cable||500|
|10BaseF||Fiber optic cable||2000|
|100BaseT||Unshielded Twisted Pair||100|
|100BaseTX||Unshielded Twisted Pair||220|
peak operating speed of around 54 Mbps
- 802.11a – wireless network bearer operating in the 5Ghz ISM band with data rate up to 54 Mbps (orthogonal frequency division multiplex)
- 802.11b – wireless network bearer operating in the 2.4Ghz ISM band with data rate up to 11Mbps (direct sequence spread spectrum)
- 802.11e – quality of service and prioritization
- 802.11f – handover
- 802.11g – wireless network bearer operating in the 2.4 Ghz ISM band with data rates up to 54Mbps
- 802.11h – power control
- 802.11i – authentication and encryption
- 802.11j – internetworking
- 802.11k – measurement reporting
- 802.11n – stream multiplexing
- 802.11s – mesh networking
Of these standards, the most widely known are the network bearer standards, 802.11a, 802.11b, and 802.11g
The range of WIFI is limited to around 50 meters.
-721kbps, 3 channels
-communications to be established between devices up to a max distance of 100 meters
-running in the 2.4Ghz ISM band, Bluetooth employs frequency hopping techniques with the carrier modulated using Gaussian Frequency Shift Keying (GFSK)
-The standard uses a hopping rate of 1600 hops per second. These are spread over 79 fixed frequencies and they are chosen in a pseudo-random sequence. The fixed frequencies occur at 2400 + n MHz where the value of n varies from 1 to 79. These gives frequencies of 2402, 2404… 2480 MHz. In some countries, the ISM band allocation does not allow the full range of frequencies to be used. In France, Japan and Spain, the hop sequences has to be restricted to only 23 frequencies because of the ISM band allocation is smaller.
-For correct operation, the level of BT is set to 0.5 and the modulation index must be between 0.28 and 0.35.
-Power class 1 is designed for long range communications up to about 100m devices, and this has a maximum output power of 20dBm, next is Power Class 2 which is used for what are termed for ordinary range devices with a range up to about 10, with a max output power of 4dBm. Finally, there is Power Class 3 for short range devices. This support communication only to about 10 cm and it has a max output power of 0dBm.
-The transmitted initial center frequency must be within ±75Khz from the receiver center frequency.
-There are two ways in which data is transferred. The first is by using what is termed as Asynchronous Connectionless Communications Link (ACL) 732.2 bits/sec asymmetric mode. When a symmetrical mode is needed with data transferred at the same rate in both directions, the data transfer rate falls to 433.9 kbits/sec. This is used for file and data transfers. A second method is termed a Synchronous Connection-orientated Communications Link (SCL) 64 kbits/sec. This is used for applications such as digital audio.
WIMAX (Worldwide Interoperability for Microwave Access)
-IEEE 802.16 standard
-point to multi-point broadband technology
-75 Mbps uplink/downlink
-Orthogonal Frequency Division Multiplex (OFDM). It is the fact that WiMax uses OFDM that enables it to occupy a wide bandwidth and carry the very high data rates. OFDM uses a large number of close spaced carriers, each modulated with a fraction of the data payload. The carriers are orthogonal to each other and in this way they do not interfere with each other.
-uses frequencies in the range 10to 66GHz (LOS)
-max ranges up to 31 miles
-WiMax can transmit data up to a distance of 48km
UWB (ultra wideband)
-FCC has mandated that the UWB transmission can legally operate in the range 3.1Ghz up to 10.6Ghz at a limited power of -41dBm/Mhz
-bandwidth of at least 500MHz, as well as having a bandwidth of at least 20% of the center frequency
NFC (near field communications)
-NFC technology operated by using magnetic field induction. It also operates within the globally available and unregulated 13.56 Mhz frequency band. However, with a maximum operating distance of around 10 cm it is unlikely to cause interference to other uses.
-The data transfer rate may either be 106, 212 or 424 kbps and there is probability of higher data rather later.
-There are also two modes of operation, namely one way (passive) or two way (active).
DECT (Digital Enhanced Cordless Telecommunication)
-developed by members of the European Telecommunications Standards Institute (ETSI) in 1992
-operates in the band 1880 – 1900Mhz
-The basic frequency plan provides for ten channels within this band.
-BT of 0.5
-The system uses dynamic channel allocation and is thereby able to reduce the levels of interference.
-The DECT radio interface employs a number of techniques in its access methodology. The scheme uses Multi-carrier, Time Division Multiple Access, Time Division Duplex (MC/TDMA/TDD).
-The basic DECT system has a total of 10 possible carrier frequencies between 1880 and 1900 Mhz, i.e. it is a multi-carrier (MC) system.
-In addition to this the time dimensions for each carrier is divided to provide timeframes repeating every 10ms. Each frame consists of 24 timeslots, each of which is individually accessibly and may be sued for either transmission or reception. For the basic DECT speech service 2 timeslots – with 5 ms separation – are paired to provide bearer capacity for typically 32kbps (ADPCM G.726 coded speech) full duplex connection.
-The DECT TDMA structure enables up to 12 simultaneous basic voice connections per transceiver.
-DECT standard defines a maximum data rate of 552 kbps with full security.
Frequency Band – 1880 to 1900 MHz
Access technique – MC/TDMA/TDD Symbol rate 1152 k symbols/s
Carrier spacing – 1728 KHz
Frame duration – 10ms
Access channels/RF carrier – 12 duplex 32 kbits/channel
Traffic channels/single radio – TRX 12
Traffic Channel assignment – instant dynamic
Control carriers – not required
Modulation – GFSK (BT=0.5) and optional higher level modulation schemes possible
LO Stability – 25 ppm
Portable average RF power – 10mW
Portable peak RF power – 240mW 24dBm
Speech codec – 32 kbits/s ADPCM
Base station sensitivity at 0.1% BER – -86dBm(for GAP) (typically -90dBm to -94dBm)
Basic link budget – 110 dBm (typ. 114 dBm to 118 dBm)
Protected 64kbits/s bearer service – yes
Base station antenna – diversity switched, post detection selection – optional
Dual antennas in handset- optional
Tolerance to time dispersion with selection antenna diversity – 200ns (500ns possible with low-cost non-coherent equalizer)