APRS ® 1200/9600 bps data communication (only on band B), using the World Standard AX25 protocol.
The built-in AX25 TNC data modem enables the use of APRS® (Automatic Packet/Position Reporting System). The Yaesu VX-8 DE and Yaesu VX-8 GE radios support APRS 1200/9600 BPS data communication. You can send your coordinates, speed, direction, which can also be seen on the screen. These data can be sent via an Internet gateway (I-Gate), and be made available for those who are authorized. This makes it available.
What does CTCSS stand for?
It is an abbreviation of Continuous Tone Coded Squelch System. Continuous Tone Coded Squelch System It is also known on other names (like Private Line at Motorola) and like sub-tone under the band. In practice it works like continuous modulation of the transmitter under the audio frequency band (300-3000 Hz) by about 1/3 of the nominal deviation. This modulation is not audible in the receiver, because the audio frequency filter of the receiver cuts these low frequency sounds, which thus do not disturb. There is a decoder built in the receiver, which senses the set audio frequency, opens the squelch and makes the received speech audible in the speaker. It is useful because the squelch will not keep opening in a noisy environment (very useful for using repeaters), and when the same frequency is used by several independently operating groups. In the latter case the user can see on the LED that the channel is busy, but does not hear the conversation of the other group. The originally 38-tone CTCSS has been extended to 50 tones. Other than the standard tones, some non-standard ones, can be set on some radios.
What does DCS stand for?
Digitally Coded Squelch. Its operation and function is similar to CTCSS, with the difference that not a continuous single-tone modulating signal is used, but a low-speed digital signal, which is decoded by the decoder of the receiver. The code table contains XX standard codes. Some radios are capable of the so-called inverse DCS coding and decoding, doubling the number of usable codes.
All About Chargers
There are two distinct varieties of chargers: the personal chargersand the industrial chargers. The personal charger is sold in attractive packaging and is offered with such products as mobile phones, laptops and video cameras. These chargers are economically priced and perform well when used for the application intended. The personal charger offers moderate charge times. In comparison, the industrial charger is designed for employee use and accommodates fleet batteries. These chargers are built for repetitive use. Available for single or multi-bay configurations, the industrial chargers are offered from the original equipment manufacturer (OEM). In many instances, the chargers can also be obtained from third party manufacturers. While the OEM chargers meet basic requirements, third party manufacturers often include special features, such as negative pulse charging, discharge function for battery conditioning, and state-of-charge (SoC) and state-of-health (SoH) indications. Many third party manufacturers are prepared to build low quantities of custom chargers. Other benefits third party suppliers can offer include creative pricing and superior performance. Not all third party charger manufacturers meet the quality standards that the industry demands, The buyer should be aware of possible quality and performance compromises when purchasing these chargers at discount prices. Some units may not be rugged enough to withstand repetitive use; others may develop maintenance problems such as burned or broken battery contacts. Uncontrolled over-charge is another problem of some chargers, especially those used to charge nickel-based batteries. High temperature during charge and standby kills batteries. Over-charging occurs when the charger keeps the battery at a temperature that is warm to touch (body temperature) while in ready condition. Some temperature rise cannot be avoided when charging nickel-based batteries. A temperature peak is reached when the battery approaches full charge. The temperature must moderate when the ready light appears and the battery has switched to trickle charge. The battery should eventually cool to room temperature. If the temperature does not drop and remains above room temperature, the charger is performing incorrectly. In such a case, the battery should be removed as soon as possible after the ready light appears. Any prolonged trickle charging will damage the battery. This caution applies especially to the NiMH because it cannot absorb overcharge well. In fact, a NiMH with high trickle charge could be cold to the touch and still be in a damaging overcharge condition. Such a battery would have a short service life. A lithium-based battery should never get warm in a charger. If this happens, the battery is faulty or the charger is not functioning properly. Discontinue using this battery and/or charger. It is best to store batteries on a shelf and apply a topping-charge before use rather than leaving the pack in the charger for days. Even at a seemingly correct trickle charge, nickel-based batteries produce a crystalline formation (also referred to as ‘memory’) when left in the charger. Because of relatively high self-discharge, a topping charge is needed before use. Most Li-ion chargers permit a battery to remain engaged without inflicting damage.
Also known as ‘overnight charger’ or ‘normal charger’, the slow-charger applies a fixed charge rate of about 0.1C (one tenth of the rated capacity) for as long as the battery is connected. Typical charge time is 14 to 16 hours. In most cases, no full-charge detection occurs to switch the battery to a lower charge rate at the end of the charge cycle. The slow-charger is inexpensive and can be used for NiCd batteries only. With the need to service both NiCd and NiMH, these chargers are being replaced with more advanced units. If the charge current is set correctly, a battery in a slow-charger remains lukewarm to the touch when fully charged. In this case, the battery does not need to be removed immediately when ready but should not stay in the charger for more than a day. The sooner the battery can be removed after being fully charged, the better it is. A problem arises if a smaller battery (lower mAh) is charged with a charger designed to service larger packs. Although the charger will perform well in the initial charge phase, the battery starts to heat up past the 70 percent charge level. Because there is no provision to lower the charge current or to terminate the charge, heat-damaging over-charge will occur in the second phase of the charge cycle. If an alternative charger is not available, the user is advised to observe the temperature of the battery being charged and disconnect the battery when it is warm to the touch. The opposite may also occur when a larger battery is charged on a charger designed for a smaller battery. In such a case, a full charge will never be reached. The battery remains cold during charge and will not perform as expected. A nickel-based battery that is continuously undercharged will eventually loose its ability to accept a full charge due to memory.
The so-called quick-charger, or rapid charger, is one of the most popular. It is positioned between the slow-charger and the fast-charger, both in terms of charging time and price. Charging takes 3 to 6 hours and the charge rate is around 0.3C. Charge control is required to terminate the charge when the battery is ready. The well designed quick-charger provides better service to nickel-based batteries than the slow-charger. Batteries last longer if charged with higher currents, provided they remain cool and are not overcharged. The quick-chargers are made to accommodate either nickel-based or lithium-based batteries. These two chemistries can normally not be interchanged in the same charger.
The fast-charger offers several advantages over the other chargers; the obvious one is shorter charge times. Because of the larger power supply and the more expensive control circuits needed, the fast-charger costs more than slower chargers, but the investment is returned in providing good performing batteries that live longer. The charge time is based on the charge rate, the battery’s SoC, its rating and the chemistry. At a 1C charge rate, an empty NiCd typically charges in a little more than an hour. When a battery is fully charged, some chargers switch to a topping charge mode governed by a timer that completes the charge cycle at a reduced charge current. Once fully charged, the charger switches to trickle charge. This maintenance charge compensates for the self-discharge of the battery. Modern fast-chargers commonly accommodate both NiCd and NiMH batteries. Because of the fast-charger’s higher charge current and the need to monitor the battery during charge, it is important to charge only batteries specified by the manufacturer. Some battery manufacturers encode the batteries electrically to identify their chemistry and rating. The charger then sets the correct charge current and algorithm for the battery intended. Lead Acid and Li-ion chemistries are charged with different algorithms and are not compatible with the charge methods used for nickel-based batteries. It is best to fast charge nickel-based batteries. A slow charge is known to build up a crystalline formation on nickel-based batteries, a phenomenon that lowers battery performance and shortens service life. The battery temperature during charge should be moderate and the temperature peak kept as short as possible. It is not recommended to leave a nickel-based battery in the charger for more than a few days, even with a correctly set trickle charge current. If a battery must remain in a charger for operational readiness, an exercise cycle should be applied once every month.
Charging the Nickel Cadmium Battery
Battery manufacturers recommend that new batteries be slow-charged for 24 hours before use. A slow charge helps to bring the cells within a battery pack to an equal charge level because each cell self-discharges to different capacity levels. During long storage, the electrolyte tends to gravitate to the bottom of the cell. The initial trickle charge helps redistribute the electrolyte to remedy dry spots on the separator that may have developed. Some battery manufacturers do not fully form their batteries before shipment. These batteries reach their full potential only after the customer has primed them through several charge/discharge cycles, either with a battery analyzer or through normal use. In many cases, 50 to 100 discharge/charge cycles are needed to fully form a nickel-based battery. Quality cells, such as those made by Sanyo and Panasonic, are known to perform to full specification after as few as 5 to 7 discharge/charge cycles. Early readings may be inconsistent, but the capacity levels become very steady once fully primed. A slight capacity peak is observed between 100 and 300 cycles. Most rechargeable cells are equipped with a safety vent to release excess pressure if incorrectly charged. The safety vent on a NiCd cell opens at 1034 to 1379 kPa (150 to 200 psi). In comparison, the pressure of a car tire is typically 240 kPa (35 psi). With a resealable vent, no damage occurs on venting but some electrolyte is lost and the seal may leak afterwards. When this happens, a white powder will accumulate over time at the vent opening. Commercial fast-chargers are often not designed in the best interests of the battery. This is especially true of NiCd chargers that measure the battery’s charge state solely through temperature sensing. Although simple and inexpensive in design, charge termination by temperature sensing is not accurate. The thermistors used commonly exhibit broad tolerances; their positioning with respect to the cells are not consistent. Ambient temperatures and exposure to the sun while charging also affect the accuracy of full-charge detection. To prevent the risk of premature cut-off and assure full charge under most conditions, charger manufacturers use 50°C (122°F) as the recommended temperature cut-off. Although a prolonged temperature above 45°C (113°F) is harmful to the battery, a brief temperature peak above that level is often unavoidable. More advanced NiCd chargers sense the rate of temperature increase, defined as dT/dt, or the change in temperature over charge time, rather than responding to an absolute temperature (dT/dt is defined as delta Temperature / delta time). This type of charger is kinder to the batteries than a fixed temperature cut-off, but the cells still need to generate heat to trigger detection. To terminate the charge, a temperature increase of 1°C (1.8°F) per minute with an absolute temperature cut-off of 60°C (140°F) works well. Because of the relatively large mass of a cell and the sluggish propagation of heat, the delta temperature, as this method is called, will also enter a brief overcharge condition before the full-charge is detected. The dT/dt method only works with fast chargers. Harmful overcharge occurs if a fully charged battery is repeatedly inserted for topping charge. Vehicular or base station chargers that require the removal of two-way radios with each use are especially hard on the batteries because each reconnection initiates a fast-charge cycle. This also applies to laptops that are momentarily disconnected and reconnected to perform a service. Likewise, a technician may briefly plug the laptop into the power source to check a repeater station or service other installations. Problems with laptop batteries have also been reported in car manufacturing plants where the workers move the laptops from car to car, checking their functions, while momentarily plugging into the external power source. Repetitive connection to power affects mostly ‘dumb’ nickel-based batteries. A ‘dumb’ battery contains no electronic circuitry to communicate with the charger. Li-ion chargers detect the SoC by voltage only and multiple reconnections will not confuse the charging regime. More precise full charge detection of nickel-based batteries can be achieved with the use of a micro controller that monitors the battery voltage and terminates the charge when a certain voltage signature occurs. A drop in voltage signifies that the battery has reached full charge. This is known as Negative Delta V (NDV). NDV is the recommended full-charge detection method for ‘open-lead’ NiCd chargers because it offers a quick response time. The NDV charge detection also works well with a partially or fully charged battery. If a fully charged battery is inserted, the terminal voltage raises quickly, then drops sharply, triggering the ready state. Such a charge lasts only a few minutes and the cells remain cool. NiCd chargers based on the NDV full charge detection typically respond to a voltage drop of 10 to 30mV per cell. Chargers that respond to a very small voltage decrease are preferred over those that require a larger drop. To obtain a sufficient voltage drop, the charge rate must be 0.5C and higher. Lower than 0.5C charge rates produce a very shallow voltage decrease that is often difficult to measure, especially if the cells are slightly mismatched. In a battery pack that has mismatched cells, each cell reaches the full charge at a different time and the curve gets distorted. Failing to achieve a sufficient negative slope allows the fast-charge to continue, causing excessive heat buildup due to overcharge. Chargers using the NDV must include other charge-termination methods to provide safe charging under all conditions. Most chargers also observe the battery temperature. The charge efficiency factor of a standard NiCd is better on fast charge than slow charge. At a 1C charge rate, the typical charge efficiency is 1.1 or 91 percent. On an overnight slow charge (0.1C), the efficiency drops to 1.4 or 71 percent. At a rate of 1C, the charge time of a NiCd is slightly longer than 60 minutes (66 minutes at an assumed charge efficiency of 1.1). The charge time on a battery that is partially discharged or cannot hold full capacity due to memory or other degradation is shorter accordingly. At a 0.1C charge rate, the charge time of an empty NiCd is about 14 hours, which relates to the charge efficiency of 1.4. During the first 70 percent of the charge cycle, the charge efficiency of a NiCd battery is close to 100 percent. Almost all of the energy is absorbed and the battery remains cool. Currents of several times the C-rating can be applied to a NiCd battery designed for fast charging without causing heat build-up. Ultra-fast chargers use this unique phenomenon and charge a battery to the 70 percent charge level within a few minutes. The charge continues at a lower rate until the battery is fully charged. Once the 70 percent charge threshold is passed, the battery gradually loses ability to accept charge. The cells start to generate gases, the pressure rises and the temperature increases. The charge acceptance drops further as the battery reaches 80 and 90 percent SoC. Once full charge is reached, the battery goes into overcharge. In an attempt to gain a few extra capacity points, some chargers allow a measured amount of overcharge. Figure 4-1 illustrates the relationship of cell voltage, pressure and temperature while a NiCd is being charged. Ultra-high capacity NiCd batteries tend to heat up more than the standard NiCd if charged at 1C and higher. This is partly due to the higher internal resistance of the ultra-high capacity battery. Optimum charge performance can be achieved by applying higher current at the initial charge stage, then tapering it to a lower rate as the charge acceptance decreases. This avoids excess temperature rise and yet assures fully charged batteries. Figure 4-1: Charge characteristics of a NiCd cell. These cell voltage, pressure and temperature characteristics are similar in a NiMH cell. Interspersing discharge pulses between charge pulses improves the charge acceptance of nickel-based batteries. Commonly referred to as ‘burp’ or ‘reverse load’ charge, this charge method promotes high surface area on the electrodes, resulting in enhanced performance and increased service life. Reverse load also improves fast charging because it helps to recombine the gases generated during charge. The result is a cooler and more effective charge than with conventional DC chargers. Charging with the reverse load method minimizes crystalline formation. The US Army Electronics Command in Fort Monmouth, NJ, USA, had done extensive research in this field and has published the results. (See Figure 10-1, Crystalline formation on NiCd cell). Research conducted in Germany has shown that the reverse load method adds 15 percent to the life of the NiCd battery. After full charge, the NiCd battery is maintained with a trickle charge to compensate for the self-discharge. The trickle charge for a NiCd battery ranges between 0.05C and 0.1C. In an effort to reduce the memory phenomenon, there is a trend towards lower trickle charge currents.
Charging the Nickel-Metal Hydride Battery
Chargers for NiMH batteries are very similar to those of the NiCd system but the electronics is generally more complex. To begin with, the NiMH produces a very small voltage drop at full charge. This NDV is almost non-existent at charge rates below 0.5C and elevated temperatures. Aging and cell mismatch works further against the already minute voltage delta. The cell mismatch gets worse with age and increased cycle count, which makes the use of the NDV increasingly more difficult. The NDV of a NiMH charger must respond to a voltage drop of 16mV or less. Increasing the sensitivity of the charger to respond to the small voltage drop often terminates the fast charge by error halfway through the charge cycle. Voltage fluctuations and noise induced by the battery and charger can fool the NDV detection circuit if set too precisely. The popularity of the NiMH battery has introduced many innovative charging techniques. Most of today’s NiMH fast chargers use a combination of NDV, voltage plateau, rate-of-temperature-increase (dT/dt), temperature threshold and timeout timers. The charger utilizes whatever comes first to terminate the fast-charge. NiMH batteries which use the NDV method or the thermal cut-off control tend to deliver higher capacities than those charged by less aggressive methods. The gain is approximately 6 percent on a good battery. This capacity increase is due to the brief overcharge to which the battery is exposed. The negative aspect is a shorter cycle life. Rather than expecting 350 to 400 service cycles, this pack may be exhausted with 300 cycles. Similar to NiCd charge methods, most NiMH fast-chargers work on the rate-of-temperature-increase (dT/dt). A temperature raise of 1°C (1.8°F) per minute is commonly used to terminate the charge. The absolute temperature cut-off is 60°C (140°F). A topping charge of 0.1C is added for about 30 minutes to maximize the charge. The continuous trickle charge that follows keeps the battery in full charge state. Applying an initial fast charge of 1C works well. Cooling periods of a few minutes are added when certain voltage peaks are reached. The charge then continues at a lower current. When reaching the next charge threshold, the current steps down further. This process is repeated until the battery is fully charged. Known as ‘step-differential charge’, this charge method works well with NiMH and NiCd batteries. The charge current adjusts to the SoC, allowing high current at the beginning and more moderate current towards the end of charge. This avoids excessive temperature build-up towards the end of the charge cycle when the battery is less capable of accepting charge. NiMH batteries should be rapid charged rather than slow charged. The amount of trickle charge applied to maintain full charge is especially critical. Because NiMH does not absorb overcharge well, the trickle charge must be set lower than that of the NiCd. The recommended trickle charge for the NiMH battery is a low 0.05C. This is why the original NiCd charger cannot be used to charge NiMH batteries. The lower trickle charge rate is acceptable for the NiCd. It is difficult, if not impossible, to slow-charge a NiMH battery. At a C-rate of 0.1C and 0.3C, the voltage and temperature profiles fail to exhibit defined characteristics to measure the full charge state accurately and the charger must depend on a timer. Harmful overcharge can occur if a partially or fully charged battery is charged on a charger with a fixed timer. The same occurs if the battery has lost charge acceptance due to age and can only hold 50 percent of charge. A fixed timer that delivers a 100 percent charge each time without regard to the battery condition would ultimately apply too much charge. Overcharge could occur even though the NiMH battery feels cool to the touch. Some lower-priced chargers may not apply a fully saturated charge. On these economy chargers, the full-charge detection may occur immediately after a given voltage peak is reached or a temperature threshold is detected. These chargers are commonly promoted on the merit of short charge time and moderate price.
Charging the Lithium Ion Battery
The Li-ion charger is a voltage-limiting device similar to the lead acid battery charger. The difference lies in a higher voltage per cell, tighter voltage tolerance and the absence of trickle or float charge when full charge is reached. While the lead acid battery offers some flexibility in terms of voltage cut-off, manufacturers of Li-ion cells are very strict on setting the correct voltage. When the Li- ion was first introduced, the graphite system demanded a charge voltage limit of 4.10V/cell. Although higher voltages deliver increased energy densities, cell oxidation severely limited the service life in the early graphite cells that were charged above the 4.10V/cell threshold. This effect has been solved with chemical additives. Most commercial Li-ion cells can now be charged to 4.20V. The tolerance on all Li-ion batteries is a tight +/-0.05V/cell. Industrial and military Li-ion batteries designed for maximum cycle life use an end-of-charge voltage threshold of about 3.90V/cell. These batteries are rated lower on the watt-hour-per-kilogram scale, but longevity takes precedence over high energy density and small size. The charge time of all Li-ion batteries, when charged at a 1C initial current, is about 3 hours. The battery remains cool during charge. Full charge is attained after the voltage has reached the upper voltage threshold and the current has dropped and leveled off at about 3 percent of the nominal charge current. Increasing the charge current on a Li-ion charger does not shorten the charge time by much. Although the voltage peak is reached quicker with higher current, the topping charge will take longer. Figure 4-5 shows the voltage and current signature of a charger as the Li-ion cell passes through stage one and two. Some chargers claim to fast-charge a Li-ion battery in one hour or less. Such a charger eliminates stage 2 and goes directly to ‘ready’ once the voltage threshold is reached at the end of stage 1. The charge level at this point is about 70 percent. The topping charge typically takes twice as long as the initial charge. No trickle charge is applied because the Li-ion is unable to absorb overcharge. Trickle charge could cause plating of metallic lithium, a condition that renders the cell unstable. Instead, a brief topping charge is applied to compensate for the small amount of self-discharge the battery and its protective circuit consume. Depending on the charger and the self-discharge of the battery, a topping charge may be implemented once every 500 hours or 20 days. Typically, the charge kicks in when the open terminal voltage drops to 4.05V/cell and turns off when it reaches 4.20V/cell again. Figure 4-5: Charge stages of a Li-ion battery. Increasing the charge current on a Li-ion charger does not shorten the charge time by much. Although the voltage peak is reached quicker with higher current, the topping charge will take longer. What if a battery is inadvertently overcharged? Li-ion batteries are designed to operate safely within their normal operating voltage but become increasingly unstable if charged to higher voltages. On a charge voltage above 4.30V, the cell causes lithium metal plating on the anode. In addition, the cathode material becomes an oxidizing agent, loses stability and releases oxygen. Overcharging causes the cell to heat up. Much attention has been placed on the safety of the Li-ion battery. Commercial Li-ion battery packs contain a protection circuit that prevents the cell voltage from going too high while charging. The typical safety threshold is set to 4.30V/cell. In addition, temperature sensing disconnects the charge if the internal temperature approaches 90°C (194°F). Most cells feature a mechanical pressure switch that permanently interrupts the current path if a safe pressure threshold is exceeded. Internal voltage control circuits cut off the battery at low and high voltage points. Exceptions are made on some spinel (manganese) packs containing one or two small cells. On overcharge, this chemistry produces minimal lithium plating on the anode because most metallic lithium has been removed from the cathode during normal charging. The cathode material remains stable and does not generate oxygen unless the cell gets extremely hot. Important: In case of rupture, leaking electrolyte or any other cause of exposure to the electrolyte, flush with water immediately. If eye exposure occurs, flush with water for 15 minutes and consult a physician immediately. Charging the Lithium Polymer Battery The charge process of a Li-Polymer is similar to that of the Li-ion. Li-Polymer uses dry electrolyte and takes 3 to 5 hours to charge. Li-ion polymer with gelled electrolyte, on the other hand, is almost identical to that of Li-ion. In fact, the same charge algorithm can be applied. With most chargers, the user does not need to know whether the battery being charged is Li-ion or Li-ion polymer. Almost all commercial batteries sold under the so-called ‘Polymer’ category are a variety of the Li-ion polymer using some sort of gelled electrolyte. A low-cost dry polymer battery operating at ambient temperatures is still some years away.