Ports and connectors
The RS-232 port is a DB9 male connector configured as DTE. Only three pins are used, transmit on pin two, receive on pin three, and ground on pin five. Transmit is an output and receive is an input to the TX325. The RS-232 port allows the transmitter to be connected to a data logger. Refer to the following table for the cable options and data logger connection.
The RF Out connector is for attaching the transmission antenna. A properly matched antenna cable and antenna must be connected to the TX325 before transmission occurs.
Failure to use a properly matched antenna cable and antenna may cause permanent damage to the radio frequency (RF) amplifiers.
The nominal impedance is 50 ohms; the frequency range is approximately 400 to 403 MHz. Maximum EIRP for GOESV2 is 41 dBm for 300 bps and 47 dBm for 1200 bps. The antenna gain can be set while configuring the transmitter. If not set, the TX325 will use an antenna gain of 11 dBi and a transmitter-antenna cable loss of 1 dB. Under those conditions, at 300 bps transmission rates, the maximum transmit power from the transmitter is 31 dBm. At 1200 bps, the transmit power is 37 dBm.
Effective Antenna Gain is defined as antenna gain (in dBi) minus the transmitter-antenna cable loss (in dB). If the Effective Antenna Gain is set and enabled, the transmitter automatically adjusts the radio power output to limit the EIRP to the maximum allowed value. The adjusted power output may be up to 37 dBm, depending on the Antenna Gain and Baud Rate settings.
The GPS port on the TX325 is an SMA female connector for attaching an active 3.3 V GPS antenna. Operation without a GPS antenna connected will not cause damage, but the transmitter will not transmit without a valid GPS fix. The transmitter uses the GPS receiver for two functions. The precise GPS time is used to ensure scheduled transmissions occur at the proper time. The one-second GPS synchronization pulse is used to ensure a precise, drift-free carrier frequency.
The TX325 power connector has two pins: ground and 12 V for connection of the power supply. The input power requirement is 10.5 to 16 VDC can use up to 2.5 A. A power supply consisting of a CH150, CH200, or CH201 regulator, BP12 or BP24 battery, and a solar panel typically can support these requirements. The regulator connects to the TX325 power connector.
The TX325 should never directly draw power from the data logger. The transmitter draws 2.5 A of power during transmission. The data logger can provide a maximum of 0.9 A over its 12 VDC terminals, which is insufficient. To avoid transmission issues, ensure that the TX325 power is directly connected to the charging regulator or the battery.