Repeater Basics: What is a 2-way radio repeater and how is it used? April 24, 2015 10:58 3 Comments

What is a Repeater?

In the world of modern communication there is an ever increasing need for providing higher outreach. The traditional portable radios offer limited coverage area. However, a dedicated transceiver can help us achieve the requisite coverage.

A repeater is essentially a communication device which acts as a link between two radio operators to cover a large area. If you need a large coverage area like your 50,000 acre ranch, city, county or even an entire state, a repeater system comes in handy.

How it Works?

It is a two-way radio frequency communication system which receives a frequency from portable two-way radios, and re-transmits it at another frequency in real-time, albeit at a higher wattage than typical portable radios. This mechanism allows repeaters to broadcast to a much wider reception spectrum. Since it is capable of both transmitting and receiving at the same time, it is also called a ‘Transceiver’.

Additionally, two-way radio repeaters can communicate with all RF (radio frequency) receptors operating on the same RF channel. Since they use two different RF channels to carry the transmitted and received information frequencies, they can be truly bi-directional without any dependencies or interference with each other.

This operational mode is known as ‘Duplex’ operation – which means a discrete channel is dedicated for each direction. It can be further divided into two types:

  • Half-duplex: A push-to-talk button switch is used to signal the commencement of trans-receiving
  • Full-duplex: Mobile telephones with ability to transmit and receive at the same time

While it allows better communication, power and extended range, if a radio can’t use a repeater, it wouldn’t be able to communicate at all.

Many modern two-way radio repeaters also indulge in ‘Hybrid’ operation, where they use duplex as a default but are capable of operating like a Simplex (single channel) trans-reception if the devices are out of range. Such devices are functional both on fixed RF channels or able to pick a physical RF channel for communication depending on pre-determined availability or channel assignment logic.

Repeater components

The prominent components of a two-way radio repeater as shown above are:

  1. Receiver – accepts the incoming signal. It is advisable to use a sensitive equipment to allow reception of even the weaker transmissions. Decoding of encrypted private-line (PL) signals occur here. Most receivers also employ a circuitry called Continuous Tone-Coded Squelch System (CTCSS) to mitigate tone squelch, or the annoyance of listening to other users on a shared communications channel, as it often happens for a two way radio.
  2. Transmitter – audio signals from sources like mobile device/ HT are boosted using power amplifiers (typically 40-100 watts or more) and transmitted to travel farther. Most transmitters are also fitted with ‘exciter’ to modulate the audio. The separation between the transmission and reception frequencies can range from 500 kHZ to 5mHZ, depending on the bandwidth. This separation is called ‘Offset’. It prevents the repeater from hearing itself or interference from its own source signals.
  3. Antenna – high-gain, high endurance, bi-directional antenna is used to both transmit and receive signals. It is advisable to mount it at a significant elevation above ground level to steer clear of obstacles. Performance demands cause them to be pretty expensive.
  4. Feed Line – low loss aluminum cables are typically used for antenna feed and signal reception from source. These are considerably better for performance than regular coax, permitting signals even from relatively weaker sources to be retained
  5. Controller – at the heart of any repeater operation is a controller. It can intuitively activate the transmitter in timely fashion, identify repeater station ID using voice/CW signals, send out pre-recorded messages, announcements and performs many other programmable tasks.

Why use repeaters?

Your portable radio, like the BCH-220, or transceiver device is limited by factors which disallow high-quality radio frequency communication, unless a repeater is used to amplify the quality

Antenna height with respect to the radio horizon – typically, a six feet high radio frequency transmission can only cover a maximum of approximately 7 miles, even if the communication channel is lossless (it never is!), due to the curvature of the earth.

Courtesy of hamradioschool.org

Photo: hamradioschool.com
  • Radio frequency (RF) attenuation in air, water and surroundings – air, water, man-made structures and several other physical obstructions impede the transmission, while absorbing some amount of signal. This in turn, means that a regular power transmission is rarely received at same strength.
  • FCC (Federal Communication Commission) narrow-banding limits – commercial or personal frequency band limits are strictly regulated by the FCC. This causes considerable bottleneck and need for higher wattage from repeaters to maintain signal fidelity. (The special frequency bands are usually reserved for emergency, military use etc.)
  • Repeaters use efficient feed lines, high gain antenna systems and receivers which are designed for heavy-duty operations for extended periods of time and exhibiting low loss properties. Taller antenna and receptors which are mounted to steer clear of limitations like earth’s curvature and physical hurdles provide further justification for their use.

Selecting the appropriate Repeater

Two-way radios are available in several different configurations. Picking the appropriate system depends as much on your experience and needs. The popularly known configurations are: hand-held portable configurations (BCH-700), mobile (BCM-220)and base configurations. They are generally operated in half-duplex mode with a ‘push-to-talk’ button to activate communication.  A cellphone/ mobile device is more akin to a full duplex operational mode. The frequencies used are also reliant on the requirements. Do remember, that line-of-sight communication is typically the strongest, while shadowing of buildings or natural obstruction will always cause some loss in transmission.

Unit frequency UHF – Ultra high frequency VHF – Very high frequency
Use Ideal for use indoors, reinforced concrete structures, or high-rises in a city landscape. Due to high obstruction, the higher frequencies are desirable. Emergency services like fire department, paramedics and police also use these to avoid the transmission bottlenecks. Handy for general residential area, rural terrain or for groups trying to keep in touch while hiking, road-trips, camping or similar outdoor operations.
Range 2-12 miles (mobile to portable)0.5 to 6 Miles (portable to portable)

25+ miles (with repeater)

2-10 miles (mobile to portable)0.25 -5 miles (portable to portable)

20+ miles (with repeater)

Another frequently asked question is whether the preferred device of choice must be analog or digital. Traditionally, analog devices have served the purposes of two-way repeater functions pretty well. Digital two-way repeater units come with some distinct advantages like:

  1. Clarity of voice signal transmission
  2. Higher security
  3. Better and sustained strength of signal coverage. Since the controls are precise, you can always calibrate and re-adjust depending on the location

However, if your business or personal needs don’t fall under any of the above categories, you are most likely not going to need it.

To sum it up, this basic information could get you started with identifying the two-way radio repeater of your choice. There are other considerations like licensing your station, aligning with local operations, adjusting offsets and ID protocols while transmitting signals. We shall join you there very soon!

For more information about BridgeCom Systems line of BCR Repeater, BCH Handhelds and BCM Mobile radios click here and pick a category. You can also contact us for more information, we are here to help.