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AMATEUR RADIO By GARRY CHATT, VK2YBX Build this line isolation unit for phone patch operation At long last, amateurs can legally hook up to the telephone lines. Here we describe a Telecomauthorised Line Isolation Unit for amateur phone patch operation. Since 1980, when Third Party Traffic privileges were announced by the Minister for Posts and Telegraphs, amateurs have been frustrated by red tape and government regulations in their efforts to operate phone patch legally. Despite many representations on behalf of Australian amateurs, phone patch remained illegal until the announcement of a recent agreement between Telecom and the WIA. This agreement allows the use of a Telecom-authorised Line Interface Unit (LIU) to link amateur radio equipment to the Public Switched Telephone Network (PSTN). Apart from the original third party objections which made the use of phone patch "expressly not authorised for personal use" or for use with the Citizens Band Radio Service or Amateur Radio Service, there existed a number of technical reasons why Telecom would not permit direct connection to the PSTN. In particular Telecom was (rightly) concerned that the safety of their telephone technicians could be compromised. Unless special precautions are taken, equipment connected directly to the telephone system can, under fault conditions, place dangerous voltages (eg, 240V) across the line. The possibility of equipment damage from precisely the same type of fault was also of The Line Isolation Unit is built into a plastic case with a plastic on-off switch. It must be built exactly as described in this article. 74 SILICON CHIP considerable concern. Commercial radio users were permitted manual or semiautomatic access to the STN provided they used a commercially designed and Telecom-authorised line isolation unit. Such devices comply with strict technical standards and provide isolation from dangerous voltages, even under fault conditions. Amateur lobbying There were, however, those in the amateur fraternity who refused to give up, notably Sam Varon VKZBVS, Jim Linton VK3PC, and Jack O'Sh_anassy VK3SP. Because of their lobbying, and that of many other amateurs as well, aH "policy" objections to phone patch use by amateurs were eventually resolved. The technical objections were solved by Geoff Donnelly VKZEGD, a Telecom designer who, with the approval of his supervisors, designed the Line Isolation Unit described here. This unit was originally described in Amateur Radio, the of• ficial journal of the WIA, and reappears here with their permission. Intending constructors should note that the cost of gaining Telecom authorisation for this Line Isolation Unit was borne by the WIA. Because of this, all units must be built in strict accordance with the design published here, and must be submitted (free of charge) to the WIA for checking prior to use (details later). Circuit details Fig.1 is a block diagram showing PARTS LIST TELEPHONE PLUG AND DOUBLE ADAPTOR EXCHANGE TELEPHONE I 1 600-ohm line isolation transformer (Telecom approved), Arlec 45035, DSE M-1 21 0, Jaycar MA-1510 1 plastic zippy box with plastic lid, DSE Cat. H-2851 . 1 DPDT switch (plastic), DSE Cat. S-1393 2 banana sockets 4 adhesive rubber feet 1 Telecom cord, part number 4544/16/1800 (available from Telecom Business Offices) 1 Telecom 605 plug 1 telephone double adaptor 1 LED mounting bezel RADIO PHONE PATCH APPROVED LIU TRANSMITTER -----RECEIVER Fig.1: the Line Isolation Unit (LIU) is plugged into a telephone double adaptor socket, in parallel with the existing telephone. how the Line Isolation Unit is used. Note that suitable phone-patch equipment is required to link the transceiver to the LIU. In its simplest form, this could consist of a manual switching system. This would direct the telephone line to either the receiver output or the transmitter input as appropriate. Alternatively, the more traditional hybrid circuit or some sort of relay switching system could be used. Fig.2 shows the circuit details. As can be seen, the Amateur to Telecom Line Isolation Unit is operated in parallel with a standard Telecom telephone. When S1 is closed, DC continuity is achieved via R1, R2, diodes D1-D4, and transformer T1. This means that once a call has been received or originated, the standard Telecom phone can be hung up, as the LIU will hold the line in the "looped condition". Zener diode D5, LED 1 and current limiting resistor R5 form the visual "looped line" circuit. Diode bridge D1-D4 ensures that the LED will light regardless of line polarity. Capacitors C1-C3 prevent RF energy from reaching the diode bridge. If this was not done, detected RF would appear as noise on the telephone line. R1 and R2 also provide RF protection and some degree of current limiting should T1 's primary short circuit. On the amateur side of T1, R4 and R5 provide current limiting in the event of an RF source being placed across the line. C4 limits the current through D6 and D7 if 240V AC is accidentally connected to the LIU from the amateur side. The normal function of diodes D6 and D7 is to serve as an audio signal clipper. This limits the signal voltages to 0.6V peak. Longitudinal voltages are prevented from passing through the LIU by transformer T1, Note: for the purpose of this article, transverse voltages are those appearing between the two input lines. Longitudinal voltages are common mode voltages; ie, they may be AC or DC above or below earth. It is extremely important that no longitudinal voltage (eg, 240V AC) is fed into the telephone lines. The isolation transformer Semiconductors 6 1 N4004 diodes 1 3.3V 1W zener diode 1 5mm red LED Capacitors 1 2µF 440V capacitor, Jaycar EE5120 (Telecom approved) 1 2µF 100V polyester 2 0.1 µF 1 00V ceramic 1 0 .01 µF 1 00V ceramic Resistors 4 100, 0.5W 1 2200, 0.25W prevents this from happening. Safety The LIU must be able to withstand 3500V AC (RMS) at 50Hz applied between either side of the Telecom line and any external wiring to the amateur equipment. For * C4 R4 10!l o- ¥+\1f 0 2 440V I C1 2 2x1N4004 AMATEUR EQUIPMENT VIA BANANA SOCKETS 06 R5 10!l 07 100V soon S1a . . A - - - 0 2 WHITE 05 3.3V C2 0.1 100V CERAMIC TELEPHONE TYPE CORD 4S44116/1800 TO 605 PLUG 600!l C3 .01 100V CERAMIC R2 10!l 0 S1b - ~ - - - 0 6 BLUE *TELECOM APPROVED AMATEUR TO TELECOM LINE ISOLATION UNIT Fig.2: the complete circuit diagram for the Line Isolation Unit. Transformer Tl and capacitor C4 provide the necessary isolation and must he Telecom-approved components (see parts list). FEBRUARY1988 75 FROM AMATEUR EQUIPMENT Fig.3: PCB parts layout and wiring diagram. Take care with component orientation. this reason, the unit is double insulated (ie, installed in a plastic box with a plastic on-off switch). When a test voltage of 264V AC at 50Hz (with a source impedance of less than 100) is applied across the amateur side of the LIU, the voltage across a lMO resistor connected across the Telecom line side must be less than 30V peak. If you build the unit correctly according to this design, these requirements will be easily met. In particular, you must use the exact parts specified in the parts list if your unit is to satisfy Telecom standards. Construction Printed circuit boards for this project are available from RCS Radio (651 Forest Rd, Bexley. Phone 587 3491). Alternatively, you can use the PCB artwork reproduced with this article to etch your own board (Fig.4). Constructors making their own PCBs should use goodquality fibreglass circuit board, with a minimum thickness of 2mm. This grade of circuit board is called FR-4. The parts layout on the PCB is shown in Fig.3 and the accompanying photographs. Prior to assembly, check the PCB pattern carefully to ensure that there are no shorts between the tracks. Use a scalpel or Exacto knife to remove any pieces of unetched copper. No particular procedure need be followed when installing the parts on the PCB, although it's a good idea to mount the low-profile components first. Be sure to install the diodes the right way round. Similarly, be sure to orient the LED correctly - it is connected to the PCB via two 100mm-long flying leads. Sleeve the leads of the LED with plastic tubing to prevent possible contact with "live" components. The assembled PCB slides directly into the slots of a plastic zippy case (DSE Cat. H-2851). Fig.5 shows the drilling details for the case. Note that the inside wall adjacent to the cutout for the moulded Telecom cable grommet must be filed to a thickness of 2mm. It will also be necessary to file a slot in the lip of the lid to clear the grommet. You can now fit the switch, LED and banana sockets to the case and complete the wiring to these items as shown in Fig.2. Now comes the tricky part: that of connecting the Telecom cable to the PCB. The problem here is that the leads of this cable are terminated by small connectors which are crimped to plastic-covered tinsel (not wire). If these are heated excessively (by soldering), the connectors will separate from the tinsel and you'll have to discard the cable and buy a new one. The solution is to make up two small spade terminals which will accept the crimp connectors on the Telecom cable. You can do this by AIIATIUII TO TRLICO■ LINI IIOLATION UNIT Fig.4: etching pattern for the PC board. 76 SILICON CHIP be operated in parallel with the telephone. Note that only the blue and white wires are connected to the PCB. The red and black wires can be cut off at the grommet. The other end of the cable is terminated with a standard Telecom 605 plug. This is plugged into a telephone double adaptor in parallel with the telephone. Telephone double adapators and plugs are available through electronics stores. The Telecom cable can be purchased from Telecom Business Offices. Alternatively, you can buy an extension cable and adapt it to suit the LIU by removing the socket. Rules of operation The PCB slides directly into the grooves in the plastic case. Note that the Telecom cable is connected to spade terminals on the back of the PCB. FRONT VIEW 158 REAR VIEW - - ~ 1 0 DIA. •~-¥10DIA. lr, I: 30 I 120 DIMENSIONS IN MILLIMETRES Fig.5: drilling details for the plastic Zippy case. hammering flat two 12mm lengths of 16-gauge tinned copper wire until they are a tight fit into the crimp connectors. The two terminals are then re-tinned, bent through 90° at their mid-points, and soldered to the "line" pads on the copper side of the PCB. No connection is made to the "phone" pads on the PCB. These were made redundant when Telecom agreed that the LIU could The normal mode of phone-patch operation is restricted to a home station, and only at one end of a radio link. In a normal single-ended phone-patch connection, the relevant third party regulations apply. Phone-patch access for mobiles is permitted via a home station, but not directly via a repeater. Repeater contacts can be phonepatched, but only by a home station. Under WICEN operation (as distinct from "normal" operation), or other emergencies involving natural disasters or life' threatening situations, double-ended phonepatch operation will be permitted as a special condition. Under duly authorised WICEN exercises, training involving the use of double ended phone-patch will be permitted on a self regulatory basis by the WIA. The WIA will be responsible for authorising such exercises and will keep a record of such exercises and training arrangements. These records will include the details of radio amateurs involved, their callsigns, and the period of authorisation. This authorisation procedure will be available to any radio amateur wishing to establish local community emergency arrangements to the WIA's standard of service. This can include appropriate community service activities, and public displays of the hobby. Operating guidelines To operate phone-patch legally, the following guidelines must be observed: FEBRUARY1988 77 (1) Only Telecom authorised equipment may be connected to the telephone network. (2) Operators must use phonepatch in accordance with Department of Transport and Communications regulations, particularly in relation to handling Third Party traffic, and must provide station identification at least every 10 minutes. (3) Brief the phone party on what is acceptable and unacceptable conversation over an amateur radio link. Any matter which is profane, obscene, or otherwise objectionable is not permitted. Transmissions from Third Parties must be limited to remarks of a personal nature, for which, by reason of their unimportance, recourse to the public telecommunications network is not justified. No commercial communication of any sort is permitted and no charge can be made by amateurs for providing a phone patch. Do not hesitate to interrupt a conversation being patched through your station if you consider that it may breach regulations. (4) Explain that the patched conversation will be one way at a time, and that each party should indicate that it is the other person's turn to speak by saying "over". (5) Keep in mind that the quality of the phone-patch relies on the standard of "off air" signals, and that the transmission of poor quality signals from an amateur station is not permitted. A poor quality patch will not assist either party, and will give amateur radio a bad name. (6) Avoid putting to air unnecessary dial clicks and telephone tones. (7) If you, as a radio amateur, use the telephone end of a phone-patch, avoid the use of your callsign if the transmission is on a band for which you are not authorised. Approval procedure Prior to connection to any Telecom lines, the LIU must be submitted for approval to the Wireless Institute of Australia, VK2 Division, PO Box 1066, Parramatta, NSW 2150. You should also include your callsign, name, address, telephone 78 SILICON CHIP Close-up view showing how the Telecom cable is connected to the two spade terminals on the back of the PCB. The terminals can be made from tinned copper wire. The completed unit with a Telecom authorisation label attached. number and return postage. When the unit is received, it will be passed on to Telecom for inspection and testing. If all is well, the unit will be returned to the constructor, with an authorisation label attached. This label will contain an individual serial number and must remain on the LIU as proof of inspection. Returned units will be accompanied by two relevant connection forms. However, as this unit is authorised for self-connect, these forms will serve only as a notation on Telecom records that the equipment for your location is authorised for use. You will also be debited $24 per year "rental" which will automatically be billed to your telephone account. Recommended reading "Interconnection of Mobile, Amateur and Citizen Band Radiocommunication Services with the Public Switched Telephone Network", Policy and Conditions Issue 2, June 1985. Available from Telecom Regulatory Branch, Melbourne. Acknowledgements The author wishes to acknowledge the following for their assistance in the preparation of this article: The Wireless Institute of Australia (WIA), VK3PC, VK2EGD, VK2ZPW, Telecom Regulatory Branch (Melbourne), and RCS Radio Pty Ltd (Sydney).~