Although tag code records can be stored in a number or ways, the simplest method is to use the transceiver buffer. The number of records that can be stored will depend on the transceiver and whether additional data, such as the time, date, and antenna ID, are recorded along with the tag code. For example, the FS1001M transceiver can store complete records for 5,350 tags and 146 lines of diagnostic information.
However, there is no backup data if the transceiver stops functioning: if the buffer file is lost, all data are lost. Diagnostic information is also erased when the transceiver is turned off.
Detection data can also be sent to an external storage device such as a laptop or low–power single–board computer, PDA, or customized data logger. Any of these devices can be connected to the transceiver serial port using a data cable.
An external device can save data in individual files named by site and date–time , i.e., the external device can both organize and back up the data.
In addition to cost, the choice of an external storage device will depend on these factors:
Laptops are often selected first due to their familiar operating systems and ease of integration into existing databases. However, their power consumption can vary greatly (20–70 W).
Any external storage device or the subcomponents used to power it can produce EMI. This EMI is easily coupled to the transceiver via the data cable. One potential solution is to use a fiber–optic modem to isolate the data cable.
Modems should be tested before installation; some have produced data transmission errors (specific brands and models are available from the authors). Furthermore, serial–port optical isolators, which depend on power from serial pins, will not work with the FS1001M transceiver.
It is often difficult to shield against the EMI radiated from a power supply. Approaches that have worked include custom chargers, which operate at frequencies outside the range of the multiplexer (the design for one is available from the authors), physical separation of the emitters (power bricks) and the reader, and physical shielding.
Temperature is another factor to consider in selecting an external data storage device. Most off–the–shelf laptops and PDAs are not environmentally hardened to withstand the large temperature swings experienced at remote sites. Hardened equipment is priced much higher than the equivalent non-hardened units; therefore, researchers often insulate the secondary enclosure.
Another consideration is that, unlike desktop computers, most laptops cannot be set to restart automatically after they stop operating due to an interruption in the power supply or to extreme temperature. A few laptops have the ability to select a restart option through the system BIOS settings. Some PDAs, low–power single–board computers, and customized data loggers also have a restart feature.
If personnel are located near a site, the least expensive way to retrieve data is to personally visit a site and download the information from the transceiver buffer to a laptop computer. Similarly, one could install a computer near the stream site and store the data continuously from the transceiver using a cable (fiber optic or RS232, depending on the distance between the transceiver and computer). Data can then be downloaded from the computer to a laptop or flash drive during site visits.
Typically, data are collected weekly using these local approaches. Both approaches have been used effectively, but over time, they have proven to be time consuming and unreliable, and they obviously do not provide real–time information on system operational status or data being collected.
Often personnel are not available locally, and to overcome this obstacle, several two–way data–communication solutions have been successfully implemented. Depending on location, budget, and project requirements, these include connecting the computer to a local digital subscriber line (DSL), to a satellite system, or to a cellular phone service.
Two–way communication allows the researcher to remotely monitor the status of equipment or upload and download information to the transceiver and ancillary equipment. This can save significant time and expense, as well as reducing the risk of data loss by retrieving data on a regular schedule, such as hourly or daily.
Monthly service charges for a two–way com link are generally less expensive than labor costs for manual data retrieval, especially from remote study sites. They also enable the researcher to know when there are problems with the system on a daily or hourly basis.
At locations where DSL is available, DSL connections have proven to be relatively inexpensive and fairly reliable. When communication failures have occurred at these sites, it appeared to be the fault of poor DSL service.
Satellite communication systems have also been used to transfer information from a local computer to a regional database. The basic equipment installed is a dish and satellite modem, which is attached to a computer connected to the transceiver.
Satellite equipment must be installed by a certified installer. These systems have been reliable, with occasional downtime caused by harsh weather conditions. A satellite connection normally costs more than DSL or cellular service, but it can be used in remote locations where other services are unavailable.
Both DSL and satellite approaches require more power than other approaches because they require locally based computers and modems. On the other hand, with both of these approaches, files containing tag and diagnostic data are permanently backed up at the site and automatically uploaded to other locations where they can be stored permanently.
For example, the Pacific States Marine Fisheries Commission has maintained a database containing tagging information and detection records for PIT–tagged salmonids from the entire Columbia River Basin since the early 1990s (PSMFC 1996). This database, PTAGIS, is publicly available via the internet and is widely used and shared by researchers in the Pacific Northwest fisheries community.
We use cellular–phone systems to transfer data at sites where cellular service is available. A cellular internet protocol data modem is connected directly to the transceiver. At locations where cellular coverage is marginal or even appears to be nonexistent, the cell signal can sometimes be boosted using an amplifier connected to an antenna.
Successful signal amplification requires a modem, cellular amplifier, and antennas. Several tests of equipment may be needed to find components that work (specific brands and models tested are available from the authors).
Advantages of the cellular–based communications system are that it can be installed by the purchaser with little instruction, does not require a local computer, and is fairly fast and reliable. Service speed and access depend in part on signal strength and number of users accessing the service at the time of information transfer. We have found that connection problems could often be overcome by accessing the site during off–peak hours.
One disadvantage to the cellular–based communications system, as currently installed, is that data are not permanently backed up at the site; though if data are uploaded to another location daily, then this is not a significant problem.
To automate the retrieval of data, we have developed a script using Tera Term Pro, a freeware terminal emulator. On a scheduled basis, the program connects to a site, downloads the transceiver buffer, examines the integrity of the tag and diagnostic data, writes a report, and then emails the report to designated addresses. The terminal emulator and script are available free on request.
As an extra precaution, data can be backed up locally by installing a pass–through serial data logger between the transceiver and modem.