During fiscal year 1997-98 three new sites (SAOB, MUSB, and DIAB) of the BARD network were permitted, designed, constructed and equipped with Ashtech Z-12 receivers by the BSL staff. Several other sites were also prepared in July-August 1998: MONB and PTRB became operational and a monument pier was installed at S300 (Figure 1).
In general, each new site uses a low-multipath choke-ring antenna mounted to a reinforced concrete pillar approximately one meter above local ground level. If possible, the reinforcing steel bars of the pillar are drilled and cemented into rock outcrop to improve long-term monument stability. Low-loss antenna cables are used to minimize signal degradation on the longer cable setups that normally would require signal amplification. Continuous telemetry is provided by a combination of radio modem or frame-relay technologies. Use of low-voltage cutoff devices to improve receiver performance following power outages was also introduced last year.