There is a natural tendency to compare two-way radios to cell phones because of how prevalent cell phones have become to the public globally. The following highlights the differences to help users appreciate the use, utility and design of two-way radios. This article discusses specifics about how each device is used and how that affects the sizes of the devices, along with a look toward the future of two-way radio designs.
Talk Time vs. Transmit-Receive-Standby
One cell-phone specification is talk time — how long a cell-phone user can talk to someone, measured in minutes, with a standard battery. A cellular call is a point-to-point call. Talk time is the summation of all the individual point-to-point calls that can be made using the cell phone. A cell-phone user is either using the cell phone or not. The phone has only two states: in use (call is on) or standby (no call).
Two-way radio is a true point-to-multipoint device, where the radio has three states: in-use (radio user is transmitting), receiving a call (radio user is listening) and standby (no call in progress). A notable difference between two-way radio and cellular is that the non-standby states are truly separate states. In cellular, when there is a call, both the transmitter and receiver are working during the full-duplex call. The cell-phone user is actually listening (receiving) and talking (transmitting) at the same time with the other person on the other end of the call. A 5-minute cell-phone call is 5 minutes in total of both transmit and receive because there is only one call going on. The majority of the battery power consumption is while the cellular transmitter is on. So the usefulness of the cell phone can be measured by how long the cell phone can be used (transmitting) with the given battery.
Conversely, the two-way radio user doesn’t have to talk (transmit) on every received message. Because of the group call nature of communications, the radio user may receive (hear) a lot of messages that are not specifically for the radio user, but the radio user still needs to monitor the activities. For example, a two-way radio user may hear (receive) 30 messages within 1 hour, but only respond (transmit) to three of those messages. Assuming that each message lasts only 2 seconds each, then the radio is transmitting only 6 seconds (three messages by 2 seconds each) in total, receiving for 60 seconds (30 messages by 2 seconds each), and in standby mode for the rest of the hour that the radio is not transmitting or receiving (3,600 seconds minus 60 seconds receiving minus 6 seconds transmitting or 3,534 seconds).
This gives us the cycle time of the two-way radio user (transmit-receive-standby): 6-60-3,534 seconds or 0.167-1.667-98.167 percent. Most two-way radio cycle times are specified using a 5-5-90 percent cycle time assumption, where there is a 5-percent transmit, 5-percent receive and 90-percent standby. This scenario doesn’t mean that for every received message there is one transmit message of equal duration, although it is possible. It is also possible that the 5-percent receive is spread out across the 1 hour in many short messages, while the 5-percent transmit could be from one long transmission within that same hour. The transmit-receive-standby cycle time is determined by how the organization communicates, how the individual radio user manages his/her communications, the type of work activity, the criticality and urgency of the call, and how unique each message is. The transmit-receive-standby cycle time is a more useful way to measure and compare two-way radio specifications and performance than just simply talk time. It also provides a common basis to which all two-way radios perform in power consumption.
If the radio users exceed the 5-5-90 percent cycle time, then a high-capacity battery may be required to meet a full eight-hour work shift. A high-capacity battery will add more weight and size to the portable radio. Indeed, some system owners will buy larger batteries that go beyond an eight-hour shift to plan for emergencies and disasters.
Consumer Technology First
Many technology breakthroughs usually go into consumer products first, for two reasons:
1. During initial introduction of products based on the new technology, the specifications tend to be targeted to consumer or commercial-grade specifications, such as 0º to 50° Celsius, because it’s easier to meet. It is only through refinements and additional research and development (R&D) where products with more industrialized specifications, such as -30º to +60° Celsius, are created, because the industrial specifications are harder to achieve.
2. The component manufacturers will usually sell into the consumer and commercial-grade product manufacturers first because they have significantly higher volumes. This will give a faster financial rate of return to those component manufacturers, as opposed to the industrial products, where the volume of components is less than the consumer and commercial product market.
The good news is that portable two-way radio size has been shrinking during the past three decades. Two-way radios are becoming more powerful in processing power as well. Since the introduction of microprocessors and software, two-way radios have made significant gains in features and functions, more rapidly than the physical size improvements. This trend shows no signs of stopping. We can expect that portable two-way radios will continue to advance in features and functions.
As technology advances in many other industrial areas, those advancements will find their way into two-way radio design. Future two-way radio size reductions depend on technology advancements in many other areas. Specifically, semiconductor miniaturization technology is required to make smaller components, such as power amplifiers, microprocessors and chipsets. Battery technology must also advance to create lightweight batteries that still provide the proper amperage while being safe. Metal and metallurgy technology must also evolve to discover new lightweight materials that have better heat dissipation, while maintaining strength. Materials technology will also have to advance to create lighter, yet strong, plastics for housings and sealing.
Because of competition, two-way portable radio manufacturers try to make the smallest, lightest and most robust product possible and will use the most up-to-date technologies in creating the best product. The manufacturer who spends the most in R&D usually leads the market with the most technologically advanced portable radio products. The proliferation of attractive consumer products is also affecting industrial designs, where color and attractive graphical user interfaces have crept into portable radio designs.
Two-way radios are gaining popularity globally. In the United States and Western Europe, where two-way radios have been used since the 1940s, professional users have always understood that two-way radios are always larger than cell phones. In the rest of the world, where cell-phone popularity is more prevalent than two-way radio and was more widely deployed ahead of two-way radio, cell phones have set the size expectation for personal communication devices. End-user operational requirements, the environment in which two-way radio is used, and the limits of technology drive the basis for two-way radio design.
David Lum is director of product and support operations for Asia/Pacific with Motorola based in Schaumburg, Illinois, USA. He is an editorial adviser to RadioResource International. Email comments to firstname.lastname@example.org.