mills@DCN6.ARPA (07/03/86)
Folks, From the vast volume of inquiries received here, it seems a number of players may be hooked on the time game. For them the following list of timetickers is recommended as a source of radio clocks. All of the radio clocks listed consist of a lunchbox-size gadget with an antenna connector at one end and a serial RS-232 connector at the other. You mount the antenna on the roof, snake the feedline down the elevator shaft and plug into the gazinta side, then plug the gazouta side to a spare serial port on a friendly host, say at 1200 bps. All the clocks provide an ASCII serial timecode message, some in response to a poll character, some gratuitously. All include a flashy LED display which can be peeked through the machine-room window for everybody to set their watches by. It should be understood that the technology with which all of these clocks operate is not completely reliable. Extensive experience with all of these clocks suggests that gross errors can sometimes occur, even in the most accurate and expensive models. The only solution to this problem is redundancy, perhaps along the lines suggested in RFC-958. ------------------------------------------------------------------------------ Model 468-DC Satellite Synchronized Clock Kinemetrics True Time Division 3243 Santa Rosa Avenue Santa Rosa, CA 95401 (707) 528-1230 Source: GOES geosynchronous satellite (468 MHz) Accuracy: 0.1 ms nominal Price: about $2500 with antenna This clock is synchronized by signals transmitted from a Geosynchronous Orbit Environmental Satellite (GOES), two of which were originally positioned over the eastern and western sides of the country, but only one is believed in operation now. With the present uncertainty in the space program, it is not clear that this service can survive forever. The antenna is a UHF planar array (a high-gain helical antenna is an option), which must be positioned for line-of-sight access to the satellite and connected to the receiver with low-loss coaxial cable. The receiver is relatively immune to radio propagation conditions and electrical storms. ------------------------------------------------------------------------------ Model 8170 WWVB Synchronized Clock Spectracom Corporation 101 Despatch Drive East Rochester, NY 14445 (716) 381-4827 (Tom Donaher) Source: WWVB Boulder, Colorado (60 kHz) Accuracy: 0.1 ms nominal Price: $2250 plus $250 for antenna This clock is synchronized to signals transmitted by the WWVB LF radio station in Boulder, Colorado. This is probably the most reliable and accurate source of NBS radio time at present, but can be subject to occasional service interruptions due to radio propagation conditions and electrical storms. The antenna consists of a tee-shaped ferrite rod mounted on a short boom, which can be mounted on the roof clear of metal obstructions, but not necessarily with line-of-sight access to the transmitter. An "on-time" signal generated by the receiver can be used in conjunction with the serial ASCII timecode, but this is important only for accuracies in the ten-millisecond range or better. ------------------------------------------------------------------------------ Model GC-1000 Most Accurate Clock with Model GCA-1000-1 RS-232C Output Accessory Heath Company Benton Harbor, MI 49022 Source: WWV Ft. Collins, Colorado, or WWVH Maui, Hawaii (5/10/15 MHz) Accuracy: 100 ms nominal (when synchronized) Price: about $300 kit, $425 assembled and tested This clock is synchronized to signals transmitted by the WWV or WWVH HF radio stations in Ft. Collins, Colorado and Maui, Hawaii, respectively. This is the least reliable and accurate (and cheapest) source of NBS radio time at present, but is subject to frequent service interruptions due to radio propagation conditions and electrical storms. The receiver normally scans three of the five WWV/WWVH broadcast fequencies (5/10/15 MHz) and locks to one of them as available. Since the eleven-year sunspot cycle, which is the primary determinant of radio propagation conditions, is presently near its minimum, and conditions during Summer are usually the worst, the receiver can coast for days without locking to the transmitter. During such periods the accuracy can degrade to the order of seconds. A suitable antenna clear of metal objects and RFI generated by computing machinery is vital for acceptable performance. This normally takes the form of a wire dipole, perhaps 10-30 meters long strung between poles and fed with coaxial cable and a balun. Any amateur operator or shortwave enthusiast knows exactly how to construct and install such a thing. ------------------------------------------------------------------------------ There are many other sources of radio time, but few suitable radio clocks are known to be available for them. These include: Canadian standard-time station, CHU Ottawa, Ontario, operates on 3330, 7335 and 14670 kHz and ordinarily provides more reliable service than WWV/WWVH, at least on the East coast. However, its signal format is not compatible with WWV/WWVH. There very likely may exist sources for radio clocks which operate using this station. United Kingdom standard-time station MSF also provides time signals for which at least one radio clock (last known residence at University College London) exists. Some local TV stations, including Channel 5 in the Washington area, are synchronized to precise standards (this happened in response to NBS prodding some time ago). The major TV networks are also synchronized to these standards; however, their local affiliates often operate using frame buffers which allow local origination without frame-slipping when switching to and from the network feed. This of course distroys the usefulness of the method. While those stations that are synchronized can be used to calibrate local time standards, they are unsuitable as a regular source of time. The many Loran-C navigation stations operated by the Coast Guard and scattered throughout the world transmit pulse-coded signals on 100 kHz and are synchronized precisely to NBS time. While a byproduct of accurate navigation is accurate time (and vice versa), the specialized receivers, some of which are turning up at surplus outlets, would need extensive modification to serve as radio clocks. The several Omega navigation stations operated by the Navy and providing worldwide service transmit continuous-wave signals on discrete frequencies in the 10-13 kHz (!) range and are synchronized precisely to NBS time. Very special receiving equipment is required, which is probably not suitable to radio clocks. Dave -------