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AMATEUR RADIO BY GARRY CRATT, VK2YBX AR2500 multi-mode scanner has memories galore! The old adage that "good things come in small packages" is becoming increasingly true due to advances in technology. These days, the more features that are added, the smaller the equipment becomes. This is particularly the case when considering the performance now achievable in amateur communications equipment. One area in which there have recently been great advances is that of scanning receivers. Until recent times, scanner enthus~ iasts have been limited to a choice of 20, 50 or 100-channel models. With the advent of "electronically erasable programmable read only memories" (EEPROMs) and the increased speed achievable with microcomputers, manufacturers are now able to produce small scanning receivers with incredible frequency coverage and memory capacity. One such product which takes full advantage of this technology recently crossed our desk for review. It is the The AR2500 synthesised scanning receiver offers contim1ous coverage between 500kHz & 1500MHz and features AM, FM, wideband FM & SSB/CW reception. It has 1984 memory channels & can he interfaced to a PC via an RS232C port. AR2500 scanning receiver from AOR, the noted Japanese communications product supplier. The AR2500 is a fully featured multi-mode synthesised scanning receiver offering continuous coverage from 500kHz to 1500MHz. The unit allows AM, FM, wideband FM and SSB/CW reception, thanks to an inbuilt BFO. It has an incredible 1984 memory channels and, in addition, allows for computer control via an RS232C port located on the rear panel of the scanner. This facility allows asynchronous communications with a personal computer for spectrum display and database compilation. Scanning speed What is so amazing about this receiver is that the high-speed microprocessor allows a scanning speed of 40 channels per second. In addition, the use of triple conversion in the receiver eliminates the majority of "birdies" commonly encountered in wide-range moriitor receivers. The unit is built into a plastic case which is approximately DIN car radio size, being 145mm wide, 55mm high and 163mm deep. This case has been used for previous models, including the AR950. One of the most important features offered by this receiver is the ability to resolve SSB transmissions. This feature, coupled with the HF coverage offered by the unit, means that it is an appealing receiver for both VHF and UHF scanning enthusiasts, as well as those interested in utility stations on the HF bands. Considering that the retail price of this unit is approx 60% of its nearest MAY 1991 79 competitor, the unit shapes up as good value indeed! However, there are some operational matters which vary from "the norm" to ensure good performance over the entire frequency range. In an extremely wide-band coverage unit such as the AR2500, the slowest component is that section of the receiver which must synthesise the various frequencies to be received. Compared to a conventional scanner, the AR2500 synthesiser must run through 10-15 times the normal frequ ency spread. Therefore, achieving a good scan speed is far more difficult than with a conventional scanner. The AR2500 microprocessor solves this problem by organising the scan frequencies in descending numerical order. This way the synthesiser can run rapidly as it is only required to make small steps instead oflarge steps between frequencies. Hence, to assure optimum operation with this unit , it is important to keep numerically close frequencies together in the same bank. For best results, we found that no more than 2-3MHz should be allowed between any two frequencies in a scan .::I::~::: \: .I $199 :· band. It's also best to use the same reception mode for all frequencies within the same bank. The same principle applies when linking two or more banks, where widely-spaced frequency jumps are required to go from one to the other. If large jumps are n ecessary between banks, the microprocessor will detect this, calculate the difference in frequencies and insert an artificial delay. Buffer frequencies Hence it may be advisable to enter a few intermediate or buffer frequencies in the lower numbered bank to allow sufficient transition time for the synthesiser. This will ensure the highest probability of locking onto weak signals. The unit will always move downwards in frequency within a bank and will move from the highest to the lowest scan bank and then back to the highest when the banks are linked. The speed will decrease, as will the probability of lock-on, if the order of frequencies requires large jumps from one to another. This scanner has 62 banks with each containing 32 positions, all of which are user program- mable. Any combination of banks can be linked, by simply using the LINK or UN-LINK keys. Sensitivity across the entire frequency range is excellent with quoted figures of lµV across the HF band which we found very conservative. When monitoring some HF frequencies, we found it necessary to use the inbuilt 20db attenuator to prevent overloading the receiver front end. With the attenuator in circuit, much of the noise associated with HF reception decreased while the signal remained at quite an acceptable level. The unit is supplied with a telescoping whip antenna which is only really adequate for VHF and UHF reception. A suitable long wire or dipole antenna should be used for HF reception. It should also be possible to use a discone antenna although the majority of these antennae on today's market suffer reduced performance below 25MHz. Despite the unconventional operation of this scanner, the unit has not given up its ease of operation for the sake of gadgetry. For example, if a bank has all 32 positions filled, the AR2500 displays "FULL" on the LCD ANTRIM TOROIDAL TRANSFORMERS INC. PACK. AND POST. This quality Japanese made airband receiver will suit student pilots, aviation enthusiasts, homebuilt '· ·• and ultralight owners. Small enough to fit in a shirt · pocket, the unit is easy to tune and is ideal for monitoring ATIS, local circuit frequencies etc. Provision for 2 crystal locked frequencies• (of your choice) is available. The receiver comes complete with 'iN battery, antenna, and an earpiece. 12 MONTHS WARRANTY Comprehenslve spare parts and technical information is held by our service department. ··.···•·•••·••••••:•••:•:•:•.•••••·••••·•:f..., • · • Crystals available at $29.95 each, plus $10 installation. Allow 3 weeks for delivery SpeclHClllona: MC 11110: Less than 10<18 audio variation from 2,,v to 10,000UV Frequency Cfflllll: 118 to 138MHz Pawer Consumpllon: 9V DC, 15mA (typical) Stnttlvtty: 1.4uV, for 10<18 S+N/N Slmlconduclall: 1 IC, 11 transistors, 7 diodes. ~~~(W)x115mm(H)x2Bmm(D) StlectlvHy: 180KHz at 8d8, 390KHz at 40<18 =:".!i-3:: SEND TO: AV-COMM PTY. LTD. P.O. BOX 386 NORTHBRIDGE NSW 2063, FAX: (02) 949 7095 Please send me (qty) . ... . . R537S <at> $199 ea. (Inc p. & P.I Please flt . .. .. . MHz, . . .. .MHz crystals <at> $29.95 ea (plus $10 lnllallatlonl I I I Name . Address .... .. P/code. I/We enclose cheque for $ ............. or charve to D No. Bankcard I D Visa D Masten:ard I I L Signature . . . . . . . . . . . . . . . . . . . . . . 80 SILICON CHIP Expiry Date I I I I _ I I ... II II . . ... Date . . . . . . . . . . . . . ... J * * * l SV A to 625V A available ex-stock l SV A to 2KV A available to order Largest ex-stock source of toroids in Australia * Competitive pricing available for OEMs and resellers HARBUCH ELECTRONICS PTY LTD 90 George St. HORNSBY. NSW 2077 Phone (02)476-5854 Fax (02)476-3231 TABLE 1 SIGNAL Transmitted data Received data Clear to send Signal Ground RS232 PIN NO ABBREV ACTION 2 3 5 7 (TXD) (RXD) (CTS) Data transfer PC to AR2500 Data transfer AR2500 to PC Data enable line to PC Ground screen. Pressing the DELETE button will remove a given frequency and allow a new one to be entered. The effect of this is that overwriting and accidental removal of frequencies is eliminated. Priority channels Instead of a single priority channel, the AR2500 allocates an entire bank to the PRiority function. When bank 1 is LINKed and the PRiority function activated, it is scanned after each successive bank. This means scanning follows the order 1,2,1,3,1,4,1,5. This is quite a useful function and considering the number of memory channels available, it's unlikely users will limit themselves to a single priority channel. In this case, 32 channels can be allocated the PRiority function. The AR2500 contains an 8K x 8 serial EEPROM which provides storage for the 78 frequency banks. There are 62 scan banks with 32 frequencies per bank, and 16 search banks with 2 frequencies per bank. The frequencies in all banks are sorted in descending order. The frequency information is stored in memory as a pseudo-BCD number occupying four bytes of data. The least significant byte contains mode information and the most significant three bytes con- tain the frequency. The AR2500 and a PC communicate asynchronously through an RS232C interface at 300, 1200 or 9600 baud with eight data bytes, no parity and one stop bit. To protect itself from data overflow, the CTS line is used by the AR2500 to signal to the PC that it is prepared to receive data. To send data, the PC must first send a signalling character such as a space (this is essentially a request to send character). After the first signalling character is transmitted by the PC, the AR2500 responds by taking whatever action is necessary and indicates completion of these actions by turning on CTS, thereby indicating to the PC that data may be transferred across the interface point on TXD. Automatic baud rate selection The AR2500 will automatically detect the correct baud rate. Initially, the PC must repeatedly send a carriage return character, until the scanner responds by returning a carriage return/line feed (CR.LF) sequence. The signals used on the RS232C port are shown in Table 1. TXD line Signals on this line are generated by the PC and are transferred to the .I.Sr...;.,;tt.■t;it:■h: RCS Radio Pty Ltd is the only company which manufactures and sells every PCB S front panel published in SILICON CHIP, ETI and EA. 651 Forest Road, Bexley, NSW 2207. Phone (02) 587 3491. AR2500. The PC holds the TXD line in marking "1" condition during intervals between characters or words, and at all times when no data is being transmitted. The PC will not transmit data unless an ON condition is present on the CTS line. RXD line Signals on this line are generated by the AR2500 and are transferred to the PC. RXD is held in the marking "1" position. As long as the PC is not transmitting, the AR2500 assumes that the PC is in the receive mode. CTS line Signals on this circuit are generated by the AR2500 to indicate whether or not the AR2500 is ready to accept data. Fortunately, this unit is supplied with a detailed 21-page instruction manual which outlines all valid computer commands recognised by the AR2500. There is sufficient information for an operator versed in microcomputer programming to generate custom software. In due course, software and connecting cables will be available to allow the scanner to be connected to a personal computer. This means the computer can be used to monitor and record activity (ie, mode, frequ ency, signal strength) for an extended length of time. This information can then be stored in the computer database for future reference. It will also be possible to display spectrum activity, illustrating those areas of the spectrum which suffer from congestion. This could be a valuable aid to frequency use and reuse planning. In summary, the AR2500 "wide range monitor" is an amazingly small but powerful receiver offering features previously available only on dedicated HF receivers and UHF /VHF scanners. The recommended retail price of the AR2500 is $999.00, with the price of additional software and connecting cables yet to be advised . All necessary mounting hardware and DC cords are included with the radio, which is eminently suitable for mobile use. The AR2500 should be available by the time this articl e appears in print from most reputable communications dealers. Our thanks to Access Communications Pty Ltd for the loan of the test unit. Phone (02) 417 5311. SC MAY1991 81