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AMATEUR RADIO BY GARRY CRATT, VK2YBX Kenwood's mighty little TH-28A & TH-78A transceivers The old saying that "bigger is better" is no longer necessarily correct, as we can report after checking out Kenwood's latest VHF/UHF hand-held transceiver offerings. Kenwood has released two new identically-sized hand-held transceivers: (1) the model TH-28A covering the 2-metre band, with a 70cm receive facility; and (2) the TH-78A dualband 2-metre/70cm unit. Both units offer an unbelievable range of features in such a small package. In fact, the first impression one gets of either unit is that operating it will require hours of study and a degree in Electrical Engineering. In practice, nothing could be further from the truth - they're easy to use. Designed to fit into the palm of the (Japanese) hand, both units are quite heavy, no doubt the result of the use of a diecast chassis. The units are supplied with a 7.2V 700mAh nicad battery pack which slides inside a protective cavity at the bottom of the unit. There are various power output levels available, all selectable by the Left: the TH-ZBA 2-metre FM transceiver features dual-band receiver capability (VHF/UHF) & extensive multi-scan functions. The alphanumeric display allows the user to dedicate a 6-character identifier to each of 20 memory positions. Other features include a DTMF memory function for storing up to 10 different telephone numbers plus facilities for digital message transmission. 82 SJLJCON CHIP user and dependent upon the capacity of the battery pack fitted. More on this later. The array of features is comprehensive and, in addition to the standard features expected on any basic handheld unit, includes programmable VFO tuning limits (allows the VFO to be programmed in 1MHz segments) and selectable RF output power settings of 5W, 2.5W, 2.0W, 0.5W and 20m W. These levels are dependent on the voltage and current rating of the power supply or battery used. The provision of a transmit lockout function prevents accidental transmission on a dedicated receive channel, while an in-built timer (with a maximum period of 10 minutes) prevents the "stuck microphone" problem, often the cause of blocked FM channels and particularly annoying if the frequency in question happens to be a repeater input frequency. One handy feature is the provision of a lithium microprocessor back-up battery which lasts for 20 days, even when the battery pack is removed. There are 40 user-selectable memories (50 in the TH-78A), ample for the number of dedicated FM channels in any capital city. However, the addition of the "ME-1" memory expansion unit increases this to 239 memories for those operators requiring additional capacity. Another user friendly feature is the memory channel character display, allowing the user to dedicate a 6-character alphanumeric identifier (eg, VKZRWI) to each of 20 memory positions. This is a particularly useful feature if you are travelling interstate, as the relevant repeater callsigns can be entered into memory, along with their frequencies prior to departure. This eliminates having to refer to repeater lists and amateur radio handbooks. For those wishing to scan parts of the VHF and UHF bands, both models provide nine separate scanning options, including "band scan" which instructs the receiver to scan from the lowest to the highest frequency limits and "memory scan" which instructs the receiver to scan all memory channels containing data. Unused memory channels and those deliberately locked out are skipped. The "VFO/ memory scan" function instructs the receiver to toggle between the last used memory channe.l and the VFO frequency. All scanning functions can be carrier or time interval controlled. Phone patch capability The DTMF memory feature allows telephone numbers of up to 15 digits to be stored. This is a handy feature for those involved in phone patch operations. The 3-digit dual tone squelch system (DTSS) allows squelch activation when a transmission encoded with the same 3-digit code is received. There are 999 user-selectable codes, and the duration of the code burst is extended from 250ms to 450ms to ensure reliable performance when you are using repeaters. Apart from numerals 0-9, the alphabetic characters A, B; C and D can also be used for repeater control. This feature, when used with the paging and DTSS functions, forms the basis of a digital message system. A pager facility alerts the operator to an incoming call and the DTSS feature displays the ID number of the caller. In addition, up to 10 alphanumeric messages can be kept in memory for transmission as needed, by way of reply. If the transceiver is left unattended, the last 10 digital messages (each up to six characters long) are stored in memory and can be recalled and displayed later. The "Time Alert" feature causes the transceiver to display the time the last message was received. Cross-band operation is possible with both units, although the TH-28A has no transmit facility on the 70cm band. The TH-78A allows quite extensive cross-band operations, including full duplex cross-band operation, and has the ability to receive two frequencies within the same band at the same time (either VHF + VHF or UHF + UHF). By using an external speaker, both signals can be monitored simultaneously. The TH-78A also comes equipped with the "automatic band change" function, enabling independent control of both UHF and VHF operation. Both the TH-28A and TH-78A are equipped with automatic power off and battery saver functions, to maximise battery endurance. These features, combined with user selectable RF output power settings, assist in maximising the operating hours. In addition, numerous optional accessories are available for both models. Specifically for. the TH-78A, Kenwood Australia has available the PB-17 12V 700mAh high-power battery pack, the PB-18 7.2V llO0mAh long-life battery pack, various soft cases (dependent upon the battery pack used), the BT-8 alkaline battery carrier, the PG-3H filtered cigarette lighter cord, various speaker microphones, a VOX headset (HMC-2) and a water resistant bag (WR-2). Many other options are listed and appear equally suitable for either TH78A or TH-28A. Specifications As for the technical parameters of these units, we can report that both receivers met the stated sensitivity claim of 0.18µV for 12dB SINAD and exhibited good adjacent channel rejection. Using an external 13.8V DC power supply, both transmitters drew 1.4A when operated in the high-power mode on 2-metres, while the TH-78A drew 1.5A on high power on the 70cm band. At the lowest power setting of 20mW, the TH-78A drew 120mA from the 13.8V supply. For those interested, both units use a first IF of 45.05MHz for the 2-metre receiver and 58.525MHz for the 70cm receiver. Selectivity is quoted as 60dB at 28kHz which, considering the size of the units , is adequate for UHF/VHF operations. The TH-78A has similar features to the TH-28A but is a full VHF/UHF dual-band transceiver that can receive two frequencies at the same time. A dual encoder provides independent control of the VHF & UHF bands. At the recommended price of $549 for the TH-28A and $879.00 for the TH-78A; both units offer excellent value for money. They come complete with Kenwood's 12-month warranty and are available from authorised Kenwood outlets. Acknowledgement: my thanks to Mr Yan Sabura of the Kenwood service division for his assistance in providing technical information for this article. SC MAY 1993 83