A repeater is a device that extends the range of mobile and portable radios. A repeater consists of a dedicated high-power radio unit that receives transmissions on its input frequency and simultaneously re-transmits them on its output frequency. Most repeaters have a set, band-dependant channel spacing (all repeaters on a particular band will have their input and output frequencies separated by the same amount, known as a REPEATER OFFSET).
Ham radio makes use of repeaters quite frequently, as do most commercial radio users. For very obvious reasons, scanner users need only worry about monitoring a repeater’s output or tx frequency. The most basic repeater consists of an FM receiver on one frequency and an FM transmitter on another frequency usually in the same radio band, connected together so that when the receiver picks up a signal, the transmitter is keyed and rebroadcasts whatever is heard. Ham repeaters are found mainly in the VHF two meter (144 - 146 MHz) and the UHF 70 centimeter (434 - 438 MHz) bands, but can be used on almost any frequency pair above 29 MHz.
Repeater frequency sets are known as "repeater pairs," and in the ham radio community most follow ad hoc standards for the difference between the two frequencies, commonly called the offset. In India two-meter band, the standard offset is 600 kHz (0.6 MHz), In the days of crystal-controlled radios, these pairs were identified by the last portion of the transmit (Input) frequency followed by the last portion of the receive (Output) frequency that the ham would put into the radio.
Thus "one-five seven-five" (15/75) meant that hams would transmit on 145.75MHz and listen on 145.15MHz (while the repeater would do the opposite, listening on 145.75 and transmitting on 145.15). Since the late 1970s, the use of synthesized, microprocessor-controlled radios, and widespread adoption of standard frequency splits have changed the way repeater pairs are described. Repeaters typically have a timer to cut off retransmission of a signal that goes too long. Repeaters operated by groups with an emphasis on emergency communications often limit each transmission to 30 seconds, while others may allow three minutes or even longer. The time restarts after a short pause following each transmission, and many systems feature a beep or chirp tone to signal that this has taken place.
A Band-pass/ Band-reject Filter otherwise known as Duplexer is used along with the repeater to operate on a single antenna for both transmit and receive. The Duplexer may have a set 2 or 3 cavities on both Transmit and receive side. A high gain Omni-directional antenna will be normally used at the repeater locations.
In India compared to other state/Cities Chennai is having maximum VHF repeater Stations.
Call Sign Tx Frequency Rx Frequency Location
VU2 PUM 145.600MHz 145. 00 MHz Chennai
VU2 MRR 145.775 MHz 145.175 MHz Chennai
VU3 MVR 145.675 MHz 145.075 MHz Chennai
VU3 VGC 145.575 MHz 144.975 MHz 75 KM from Chennai
VU2 VCM 145.475 MHz 145.875 MHz 150KM from Chennai
VU2 X I S 145.375 MHz 144.775 MHz 75 Km from Chennai
Due to some technical snags few of the above repeaters are not working. In a few months time all the repeaters will be operational . The First UHF repeater station in India is also located in Chennai.
VU2 MUG 434.100MHz / 435.800 MHZ
Each repeater station location and installation was a dream and it carries so much struggle/memories of different people who made it possible . The featured articles will follow with updates about the story of each repeater . In 2009 Chennai hams are trying to do more research and new ideas on the repeater maintenance , keep visiting this site for more updates.
Also this is an interesting link with info on the latest models of HAM Transreceivers from ICOM,Kenwood,Yaesu,Motorola etc . Pls check out http://www.twowayradioonline.com/