We often get asked what the best Frequency Band is. The answer to this depends on where you will mainly use a two-way radio and in what environment. The VHF Band of frequencies lies between 136 MHz and 174 MHz, while the UHF band lies between 400 MHz and 470 MHz respectively. Because UHF has many more cycles or waves per second, the wavelength is much smaller, thus allowing the RF Frequencies to penetrate buildings so much better. Therefore UHF portable radios will transmit and receive far better in an urban, built-up area than their VHF cousins. The wavelength of a 150 MHz VHF frequency is defined by the formula L = V / F, where V is the velocity of the speed of light and F is the Frequency.

The velocity of an Electromagnetic Wave of RF wave is 3 X 10⁸ or 300 million KM per second.
Frequency in this example is 150 MHz or 150 million cycles or waves per second.
Dividing the Velocity by the Frequency gives L = 3 X 10⁸ / 150 X 10⁶ or L = 300 / 150 = 4 Meters.
A UHF Frequency of 450 MHz would have a wavelength of L = 300 / 450 = 0.667 Meters.

Lastly, UHF Frequencies do not perform well in highly vegetated areas with many trees and foliage. The RF Frequencies tend to be deflected more than VHF frequencies.

So as one can see from the above explanation, one Frequency Band will be more suitable than the other. Often, especially in the Security Industry, both Frequency Bands are utilized. UHF, for on-site communications and VHF for longer distance communications, for example, vehicle to control room.

“WHAT LENGTH SHOULD MY ANTENNA BE FOR 4X4 ORRA FREQUENCIES?”

I am a user of 4X4 ORRA Channels. What should the length of the ORRA antenna be?

ORRA has three frequencies spread over 9 Channels. All the New ORRA Channels have Tone Coding. The Old ORRA Channels do not.

The Channels are:

The radio user has two choices with regard to the type of ORRA antenna you would use. The one choice is the 3dB gain antenna or 5/8 antenna as it is known.

The other choice would be the ¼ wave antenna.

Which is best? The 5/8 antenna is far better in terms of transmission and reception of radio signals than compared to the ¼ wave antenna. However, not everyone wants a long antenna mounted on their vehicles and often opt for the humble ¼ wave antenna.

The ¼ wave antenna is also more “broadband” and therefore is more suited to accommodate frequencies which are set far apart such as with the ORRA152 Frequency and the other ORRA 160 and 161 Frequencies.

If the antenna is trimmed to suit the 160 and 161 frequencies only, it would end up being too short for best 152 radio transmission. This may not be a problem at all as most of the time users will most probably be using the 1st four channels anyhow.

I would advise trimming for 160 MHz whether using a 5/8 antenna or the ¼ wave antenna. This way you will have the best-tuned antenna for the 1st four channels.

Length of the ¼ wave antenna:

L = V / F
L = 300 / 160 = 1.875 meters
L = ¼ X 1.875 meters = 0.469 meters

The exact length of course is also determined by the positioning of the antenna.

Do not cut the antenna to the calculated length above, but rather in situ, as this will take the vehicle body in account as well. I would suggest that about two to three centimetres are added to the theoretical length. Trim to final length using an SWR meter.

Length of the 5/8 antenna:

Consult the cutting chart that comes with your antenna.

As with the ¼ wave, the antenna position determines the length and pure theory does not apply.

Always transmit with the vehicle door closed and/or away from any metal objects. People standing near the antenna will also affect the readings. Ensure all the above are satisfied before transmitting. so ensure that They will affect the readings on the SWR meter. Make sure people are not standing close to the antenna while transmitting.

Call Radio Trunk for any help or advice.

“BATTERIES USED FOR TWO-WAY RADIOS”

With all the information available on the internet and various other sources, it is easy to get confused about the different radio battery types available today in the two-way radio industry. Like everything else in life, there are different horses for different courses.

This article is aimed at the most commonly used types of batteries in the two-way radio industry. I have listed them in order of their evolution and history. These are Nicad (NiCd), Nickel Metal Hydride (NiMH), Lithium Ion (Li-ion) and lastly the recent newcomer, the Lithium Ion Polymer (Li-polymer).

Every battery type will have advantages and disadvantages, depending on what is important to the user. For example, Energy Density, which is the power a battery can deliver, versus the weight of the battery. In other words, the Watt Hours per Kg. This may be important in one particular situation, while cost may important in another. In other cases, Life Cycles may be more important to the user. Life Cycles is the number of times a battery can be discharged and charged in its life.

Each battery type is still widely used, however in recent times, Lithium Ion has made huge inroads in the two-way radio market. It is extremely light in comparison to other types of batteries and this plays an important factor, especially with the more slim-line two-way radio models available today.

Since NiCd remains a standard against which other batteries are compared, we evaluate alternative chemistries against this classic battery type.

Nickel Cadmium (NiCd): Mature and well understood but relatively low in energy density. The NiCd is used where long life, high discharge rate and economical price are important. Main applications are two-way radios, biomedical equipment, professional video cameras and power tools. The NiCd contains toxic metals and is environmentally unfriendly.

Nickel-Metal Hydride (NiMH): Has a higher energy density compared to the NiCd at the expense of reduced cycle life. NiMH contains no toxic metals. Applications include mobile phones and laptop computers.

Lithium Ion (Li‑ion): Fastest growing battery system. Li‑ion is used where high-energy density and lightweight is of prime importance. The technology is fragile and a protection circuit is required to assure safety. Applications include notebook computers and cellular phones.

Lithium Ion Polymer (Li‑ion polymer): offers the attributes of the Li-ion in ultra-slim geometry and simplified packaging. Main applications are mobile phones.

Figure 1 compares these characteristics of the four most commonly used rechargeable battery systems in terms of energy density, cycle life, exercise requirements and cost.

Fig.1

Figure 1: Characteristics of commonly used rechargeable batteries

1. The internal resistance of a battery pack varies with cell rating, type of protection circuit and number of cells. The protection circuit of Li‑ion and Li-polymer adds about 100mΩ.
2. Cycle life is based on battery receiving regular maintenance. Failing to apply periodic full discharge cycles may reduce the cycle life by a factor of three.
3. Cycle life is based on the depth of discharge. Shallow discharges provide more cycles than deep discharges.
4. The discharge is highest immediately after charge, then tapers off. The NiCd capacity decreases 10% in the first 24h, then declines to about 10% every 30 days thereafter. Self-discharge increases with higher temperature.
5. Internal protection circuits typically consume 3% of the stored energy per month.
6. 1.25V is the open cell voltage. 1.2V is a commonly used value. There is no difference between the cells; it is simply a method of rating.
7. Capable of high current pulses.
8. Applies to discharge only; charge temperature range is more confined.
9. Maintenance may be in the form of ‘equalizing’ or ‘topping’ charge.
10. Cost of battery for commercially available portable devices.

Observation: It is interesting to note that NiCd has the shortest charge time, delivers the highest load current and offers the lowest overall cost-per-cycle, but has the most demanding maintenance requirements.

The Nickel Cadmium (NiCd) Battery

The NiCd prefers fast charge to slow charge and pulse charge to DC charge. All other chemistries prefer shallow discharge and moderate load currents. The NiCd is a strong and silent worker; hard labour poses no problem. In fact, the NiCd is the only battery type that performs well under rigorous working conditions. It does not like to be pampered by sitting in chargers for days and being used only occasionally for brief periods. A periodic full discharge is so important that, if omitted, large crystals will form on the cell plates (also referred to as memory) and the NiCd will gradually lose its performance.

Among rechargeable batteries, NiCd remains a popular choice for applications such as two-way radios, emergency medical equipment and power tools. Batteries with higher energy densities and less toxic metals are causing a diversion from NiCd to newer technologies.

Advantages and Limitations of NiCd Batteries

Advantages

• Fast and simple charge: Even after prolonged storage. A high number of charge/discharge cycles: if properly maintained: The NiCd battery provides over 1000 charge/discharge cycles. Good load performance: the NiCd allows recharging at low temperatures.
• Long shelf life: in any state-of-charge.
• Simple storage and transportation: most airfreight companies accept NiCd without special conditions.
• Good low-temperature performance.
• Forgiving if abused: the NiCd is one of the most rugged rechargeable batteries.
• Economically priced: the NiCd is the lowest cost battery in terms of cost per cycle.
• Available in a wide range of sizes and performance options – most NiCd cells are cylindrical.

Limitations

• Relatively low energy density: compared with newer systems.Memory effect: the NiCd must periodically be exercised to prevent memory.Environmentally unfriendly: the NiCd contains toxic metals. Some countries are limiting the use of the NiCd battery.
• Has relatively high self-discharge: needs recharging after storage.

Figure 2: Advantages and limitations of NiCd batteries.

The Nickel-Metal Hydride (NiMH) Battery

Research of the NiMH system started in the 1970s as a means of discovering how to store hydrogen for the nickel hydrogen battery. Today, nickel hydrogen batteries are mainly used for satellite applications. They are bulky, contain high-pressure steel canisters and cost thousands of Rands per cell.

In the early experimental days of the NiMH battery, the metal hydride alloys were unstable in the cell environment and the desired performance characteristics could not be achieved. As a result, the development of the NiMH slowed down. New hydride alloys were developed in the 1980s that were stable enough for use in a cell. Since the late 1980s, NiMH has steadily improved.

The success of the NiMH has been driven by its high energy density and the use of environmentally friendly metals. The modern NiMH offers up to 40% higher energy density compared to NiCd. There is potential for yet higher capacities, but not without some negative side effects.

The NiMH is less durable than the NiCd. Cycling under heavy load and storage at high temperature reduces the service life. The NiMH suffers from high self-discharge, which is considerably greater than that of the NiCd.

The NiMH has been replacing the NiCd in markets such as wireless communications and mobile computing. In many parts of the world, the buyer is encouraged to use NiMH rather than NiCd batteries. This is due to environmental concerns about the careless disposal of the spent battery.

Experts agree that the NiMH has greatly improved over the years, but limitations remain. Most of the shortcomings are native to the nickel-based technology and are shared with the NiCd battery. It is widely accepted that NiMH is an interim step to lithium battery technology.

Advantages and Limitations of NiMH Batteries

Advantages

30% to 40% higher capacity over a standard NiCd. The NiMH has the potential for yet higher energy densities. Less prone to memory than the NiCd. Periodic exercise cycles are required less often. Simple storage and transportation: Transportation conditions are not subject to regulatory control. Environmentally friendly: Contains only mild toxins; profitable for recycling.

Limitations

Limited service life: If repeatedly deep cycled, especially at high load currents, the performance starts to deteriorate after 200 to 300 cycles. Shallow rather than deep discharge cycles are preferred. Limited discharge current: Although a NiMH battery is capable of delivering high discharge currents, repeated discharges with high load currents reduces the battery’s cycle life. Best results are achieved with load currents of 0.2C to 0.5C (one-fifth to one-half of the rated capacity). More complex charge algorithm needed: NiMH batteries generate more heat during charge and requires a longer charge time than the NiCd. The trickle charge is critical and must be controlled carefully. High self-discharge — the NiMH has about 50% higher self-discharge compared to the NiCd. New chemical additives improve the self-discharge but at the expense of lower energy density. Performance degrades if stored at elevated temperatures: NiMH batteries should be stored in a cool place and at a state-of-charge of about 40%.

High maintenance: Battery requires regular full discharge to prevent crystalline formation.

About 20% more expensive than NiCd: NiMH batteries designed for the high current draw are more expensive than the regular version.

Figure 3: Advantages and limitations of NiMH batteries

The Lithium-Ion Battery

Pioneer work with the lithium battery began in 1912 but it was not until the early 1970s that the first non-rechargeable lithium batteries became commercially available. Lithium is the lightest of all metals, has the greatest electrochemical potential and provides the largest energy density per weight.

Attempts to develop rechargeable lithium batteries followed in the 1980s, but failed due to safety problems. Because of the inherent instability of lithium metal, especially during charging, research shifted to a non-metallic lithium battery using lithium ions. Although slightly lower in energy density than lithium metal, the Li‑ion is safe, provided certain precautions are met when charging and discharging. In 1991, the Sony Corporation commercialized the first Li‑ion battery. Other manufacturers followed suit. Today, the Li‑ion is the fastest growing and most promising battery chemistry.

The energy density of the Li‑ion is typically twice that of the standard NiCd. Improvements in electrode active materials have the potential of increasing the energy density close to three times that of the NiCd. In addition to high capacity, the load characteristics are reasonably good and behave similarly to the NiCd in terms of discharge characteristics (similar shape of discharge profile, but different voltage). The flat discharge curve offers effective utilization of the stored power in a desirable voltage spectrum.

The high cell voltage allows battery packs with only one cell. Most of today’s mobile phones run on a single cell, an advantage that simplifies battery design. To maintain the same power, higher currents are drawn. Low cell resistance is important to allow unrestricted current flow during load pulses.

The Li‑ion is a low maintenance battery, an advantage that most other chemistries cannot claim. There is no memory and no scheduled cycling is required to prolong the battery’s life. In addition, the self-discharge is less than half compared to NiCd, making the Li‑ion well suited for modern fuel gauge applications. Li‑ion cells cause little harm when disposed of.

Despite its overall advantages, Li‑ion also has its drawbacks. It is fragile and requires a protection circuit to maintain safe operation. Built into each pack, the protection circuit limits the peak voltage of each cell during charge and prevents the cell voltage from dropping too low on discharge. In addition, the cell temperature is monitored to prevent temperature extremes. The maximum charge and discharge current is limited to between 1C and 2C. With these precautions in place, the possibility of metallic lithium plating occurring due to overcharge is virtually eliminated.

Ageing is a concern with most Li‑ion batteries and many manufacturers remain silent about this issue. Some capacity deterioration is noticeable after one year, whether the battery is in use or not. Over two or perhaps three years, the battery frequently fails. It should be noted that other chemistries also have age-related degenerative effects. This is especially true for the NiMH if exposed to high ambient temperatures.

Storing the battery in a cool place slows down the ageing process of the Li‑ion (and other chemistries). Manufacturers recommend storage temperatures of 15°C. In addition, the battery should be partially charged during storage.

Manufacturers are constantly improving the chemistry of the Li‑ion battery. New and enhanced chemical combinations are introduced every six months or so. With such rapid progress, it is difficult to assess how well the revised battery will age.

The most economical Li-ion battery in terms of the cost-to-energy ratio is the cylindrical 18650 cell. This cell is used for mobile computing and other applications that do not demand ultra-thin geometry. If a slimmer pack is required (thinner than 18 mm), the prismatic Li‑ion cell is the best choice. There are no gains in energy density over the 18650, however, the cost of obtaining the same energy may double.

For ultra-slim geometry (less than 4 mm), the only choice is Li‑ion polymer. This is the most expensive system in terms of cost-to-energy ratio. There are no gains in energy density and the durability is inferior to the rugged 18560 cells.

Figure 5: Advantages and limitations of Li-ion batteries

The Lithium Polymer Battery

The Li-polymer differentiates itself from other battery systems in the type of electrolyte used. The original design, dating back to the 1970s, uses a dry solid polymer electrolyte. This electrolyte resembles a plastic-like film that does not conduct electricity but allows an exchange of ions (electrically charged atoms or groups of atoms). The polymer electrolyte replaces the traditional porous separator, which is soaked with electrolyte.

The dry polymer design offers simplifications with respect to fabrication, ruggedness, safety and thin-profile geometry. There is no danger of flammability because no liquid or gelled electrolyte is used. With a cell thickness measuring as little as one millimetre, equipment designers are left to their own imagination in terms of form, shape and size.

Unfortunately, dry Li-polymer suffers from poor conductivity. Internal resistance is too high and cannot deliver the current bursts needed for modern communication devices and spinning up the hard drives of mobile computing equipment. Heating the cell to 60°C and higher increases the conductivity but this requirement is unsuitable for portable applications.

To make a small Li-polymer battery conductive, some gelled electrolyte has been added. Most of the commercial Li-polymer batteries used today for mobile phones are a hybrid and contain the gelled electrolyte. The correct term for this system is Lithium Ion Polymer. For promotional reasons, most battery manufacturers mark the battery simply as Li-polymer. Since the hybrid lithium polymer is the only functioning polymer battery for portable use today, we will focus on this chemistry.

With gelled electrolyte added, what then is the difference between classic Li‑ion and Li‑ion polymer? Although the characteristics and performance of the two systems are very similar, the Li‑ion polymer is unique in that solid electrolyte replaces the porous separator. The gelled electrolyte is simply added to enhance ion conductivity.

Technical difficulties and delays in volume manufacturing have deferred the introduction of the Li‑ion polymer battery. In addition, the promised superiority of the Li‑ion polymer has not yet been realized. No improvements in capacity gains are achieved — in fact, the capacity is slightly less than that of the standard Li‑ion battery. For the present, there is no cost advantage. The major reason for switching to the Li-ion polymer is form factor. It allows wafer-thin geometries, a style that is demanded by the highly competitive mobile phone industry.

“LICENSE FREE FREQUENCIES”

In South Africa, there are two areas in the UHF Band reserved for license-free Two-Way Radio usage.

One must bear in mind that the transmission Power in these bands are limited to 500mW or 1/2 Watt, compared to the licensed band being 4 Watts.

446 MHz PMR [Private Mobile Radio] Band

PMR446 [Private Mobile Radio] is a license free service in the UHF radio frequency band and is available for business and personal use in most countries.

Coverage

PMR446 is typically used for small-site, same-building and line of sight outdoor activities. Equipment used ranges from consumer-grade to professional quality handheld or portable radios. Coverage varies greatly depending on the surrounding terrain. One would expect much less than 1KM in a city and a few KM in open countryside. If one was to be on very high ground then many kilometres could be expected.

Channels

Originally 8 channels were available in analogue mode but this has now been increased to 16 channels.

1. 446.00625 MHz
2. 446.01875 MHz
3. 446.03125 MHz
4. 446.04375 MHz
5. 446.05625 MHz
6. 446.06875 MHz
7. 446.08125 MHz
8. 446.09375 MHz
9. 446.10625 MHz
10. 446.11875 MHz
11. 446.13125 MHz
12. 446.14375 MHz
13. 446.15625 MHz
14. 446.16875 MHz
15. 446.18125 MHz
16. 446.19375 MHz

These channels are all tone coded.

463 MHz  – 464 MHz PMR [Private Mobile Radio] Band

PMR 463 MHZ – 464 MHz [Private Mobile Radio] is a license free service in the UHF radio frequency band and is available for business and personal use in most countries.

Coverage

PMR 463-464 MHz, as with the 446 MHz band, is typically used for small-site, same-building and line of sight outdoor activities. Equipment used ranges from consumer-grade to professional quality handheld or portable radios. Coverage varies greatly depending on the surrounding terrain. One would expect much less than 1KM in a city and a few KM in open countryside. If one was to be on very high ground then many kilometres could be expected.

Frequencies

463.9750 MHz
464.1250 MHz
464.1750 MHz
464.3250 MHz
464.3750 MHz

Channels are tone coded with frequencies being duplicated on successive channels on the radio.

For more information please refer to the ICASA [Independent Communications Authority of South Africa]website.

See National Radio Frequency Plan 2018.

“ANALOG VS DIGITAL TWO-WAY RADIO”

Two-Way Radio communications have been with us for many years. It has changed tremendously in recent times as technology has advanced into the Digital Age.

Radio Communication dates back to the early part of the 20th Century when it was used to communicate over the Atlantic Ocean from America to the UK. Morse Code was used in these early days and not Voice Communications.

Later, in 1923 the Australian Police used mobile radios in their vehicles. They were so large that the radio equipment would use up the entire back seat. During the 2nd World War, handheld units made their appearance. As time progressed and technologies advanced with the advent of Integrated Circuits [ IC’s ]  equipment became much smaller and compact, eventually enabling the production of much smaller handheld radios. Improvements have been made to greatly improve the quality of receivers and transmitters of Analog radios. The modern-day Analog hand-held two-way radio is a far cry from its origins in the 2nd World War.

However, the time has moved on rapidly and we are now in the Digital Age, with the advent of Digital Mobile Radio [ DMR ] in about 2012.

Digital Mobile Radio (DMR) is an open Digital Mobile Radio standard defined in the European Telecommunications Standards Institute [ ETSI ] Standard TS 102 361 parts 1–4 and used in commercial products around the world. DMR, along with with P25 Phase II, both use two-slot TDMA [Time Division Multiple Access] across the whole 12.5 KHz channel spacing, while a competitor technology, NXDN uses two 6.25 KHz slots in a divided 12.5 KHz channel spacing.

DMR has become popular with the Amateur Radio community due to the relative lower cost and complexity compared to other commercial digital modes. DMR was designed with three tiers.

DMR tiers I and II (conventional) 2005
DMR III (Trunked version) 2012

With manufacturers producing products within a few years of each publication. The primary goal of the standard is to specify a digital system with low complexity, low cost and interoperability across brands, so radio communications purchasers are not locked into a proprietary solution. In practice, many brands have not adhered to this open standard and have introduced proprietary features that make their product offerings non-interoperable.

NXDN

NXDN is an open standard for public land mobile radio systems, that is systems of Two-Way Radios. It was developed jointly by Icom Incorporated & Kenwood Corporation. It is an advanced Digital system using FSK modulation. Like other land mobile systems, NXDN systems use the VHF & UHF, frequency bands.NXDN is implemented by Icom in their IDAS system and by Kenwood as NEXEDGE. Both Kenwood and Icom now offer dual-standard equipment which supports both FDMA & TDMA standards.

NXDN uses Frequency Division Multiple-Access [ FDMA ] technology in which different communication streams are separated by frequency and run concurrently. Time-Division, Multiple-Access (TDMA) systems combine the communications streams into a single stream in which information from the different streams is transmitted in interleaved time allocations or “slots.” Code-Division, Multiple-Access (CDMA) systems allow many users to share a common spectrum allocation by using spread-spectrum techniques.

The basic NXDN channel is digital and can be either 12.5 kHz or 6.25 kHz wide. 6.25 kHz dual-channel systems can be configured to fit within a 12.5 kHz channel. This effectively doubles the spectrum efficiency compared to an analog FM system occupying a 12.5 kHz channel. The architecture of NXDN is such that two NXDN channels, within a 12.5 kHz channel, for example, can be allocated as voice/voice, voice/data, or data/data. As of 2012, this capability cannot be implemented in commercially available hardware on simplex or “talk around” frequencies, but only through repeaters.

Advantages of Digital Two-Way Radio

# Improved audio quality
# Far greater functionality
# Stronger security
# Better channel efficiency
# Longer battery life

The most obvious and attractive feature is that Digital offers two dedicated channels within the 12.5 KHz space, while Analog only offers one dedicated channel. This is very attractive both in terms of cost and in terms of functionality for the user. Now for the first time, two dedicated conversations can occur simultaneously without the one affecting the other.

Advantages of Analog Two-Way Radio

# Well understood by the public
# More natural voice
# More economical
# Very weak signals may still be received, although very degraded. Digital will cut off.

Call us for more information and advice to suit your particular requirements.