Antenna Tip of the Day!

One of the benefits of Circularly Polarized receivers is the reduction of multipath fading. e.g. if the transmitter and receiver are RHCP, the waves that become LHCP on reflection will be filtered out at the receiver due to polarization mismatch.

RS-422 Utility

In cases where a computer and the device to be communicated with are much far apart, RS-422 is the preferred serial standard. Due to differential signaling, the signal is less prone to noise and may be sent on cables as long as 1500 meters. Maximum data rate is 10 Mbps at 12m and degrades with cable length. You can use a commercially available USB-422 adapter or make one yourself to send and receive RS-422 signals on your computer. 

DC-DC Converter

Portable electronic devices often contain several sub-circuits, each with its own voltage level requirement different from that supplied by the battery. Here a DC-DC Converter is used to provide the required voltage conversion. Traco Power, Maxim Integrated, Texas Instruments and Fujitsu are some of the manufacturers of DC-DC Converter ICs.

Frequency Hopping

GSM and DCS both employ frequency hopping technique for two main advantages:

• To reduce Mulitpath Fading effect which is dependent in carrier frequency
• To randomize Co-Channel Interference (CCI)

The hopping algorithm is continuously broadcast on BCCH and MS/BTS transmits TDMA frames on different hopping carriers during a call on hopping TRX. Hopping is used on TCH, SDCCH and all Packet Data channels while BCCH and common control channels are not allowed to hop. Frequency hopping types are:

• Baseband Hopping (BBH)
• Synthesizer Hopping (SFH)
• Discrete Hopping

Sector Swap Issue in a Cellular Network

Sector Swap issue refers to the situation when cables of connected to wrong antennas, for example, sector 2 cables are connected with the sector 1 antenna and sector 1 cables are connected to sector 2 antenna. This issue can cause degraded quality, call drop, illogical hand over etc.

Power Control RxLev for GSM and DCS

The upper and lower bounds of Power Control RxLev for Downlink should be set such as signal strength is maintained slightly above the threshold of noise floor. This would provide for enough signal strength to maintain a good voice quality and keeping the interference level to the minimum. Thus, these values are kept more aggressive for DCS, being a clearer band than GSM, for instance, the upper and lower bounds for DCS are generally set to -80dBm and -90dBm as compared to GSM values of -75 dBm and -85 dBm.

Antenna Tip of the Day!

Omni-directional antennas have the advantage of more coverage while directional ones provide higher gain. Phased arrays combine the advantages of both of these by providing higher gain in all directions turn by turn.