The following FAQs are provided to assist in successful operation of the ptf 3203A and ptf 3204A GPS Time and Frequency Receivers.
Verify that a serial cable is correctly fitted between your coputer and the unit. The DB9 connection pins use the standard convention of;
Most computers with a DB9 serial port connector are configured as;
Therefore, for the computer to connect properly to the instrument, a null modem cable or null modem adapter is necessary to cross over the Tx and Rx lines, to insure the Tx from one piece of equipment is going to the Rx of the other unit and vice versa.
The usual cause of this symptom is that the settings of the serial port are incorrect, probably the baud rate. The correct settings are;
Before connecting to the Telnet interface it is necessary to set up the unit IP address and Netmask. These can be set by using the Serial Interface and using commands A24 and A25 of the menu. Typical settings would be; A24 192.168.0.19 (the IP address) and A25 255.255.255.0 (the Netmask). Alternatively, if the unit is connected to a network with a DHCP (Dynamic Host Communications Protocol) server, the unit can be set to DHCP mode and the unit will automatically acquire a network address from the DHCP server. The acquired address can be viewed by typing "help" on the serial interface and the acquired address will be shown next to command A24.
Before connecting to the HTTP interface it is necessary to set up the unit IP address and Netmask. These can be set by using the Serial Interface and using commands A24 and A25 of the menu. Typical settings would be; A24 192.168.0.19 (the IP address) and A25 255.255.255.0 (the Netmask). Alternatively, if the unit is connected to a network with a DHCP (Dynamic Host Communications Protocol) server, the unit can be set to DHCP mode and the unit will automatically acquire a network address from the DHCP server. The acquired address can be viewed by typing "help" on the serial interface and the acquired address will be shown next to command A24.
The ptf 3203A/3204A unit acts as an SNMP agent, using SNMP v1. The unit's key parameters can be viewed by an SNMP manager, and a subset of them can be also set by the SNMP manager. In addition, the unit sends "traps" to the predefined SNMP manager address. A trap is initiated when the state of the unit changes (e.g. the pulse input on channel A fails). These traps will be received by the SNMP manager on the Trap Ringer Console. Traps are enabled or disabled by command A41 on the menu.
Before connecting to the SNMP interface it is necessary to set up both the unit IP address and Netmask, and also the SNMP Manager address to which traps are to be sent. These can be set by using the Serial Interface and using commands A24, A25, and A27 of the menu. Typical settings would be; A24 192.168.0.19 (the IP address), A25 255.255.255.0 (the Netmask), and A40 192.168.0.20 (the SNMP Manager IP Address).
Alternatively, if the unit is connected to a network with a DHCP (Dynamic Host Communications Protocol) server, the unit can be set to DHCP mode and the unit will automatically acquire a network address from the DHCP server. The acquired address can be viewed by typing "help" on the serial interface and the acquired address will be shown next to command A24.
Once the IP address/Netmask has been set up and the unit is connected to a network (or directly to a computer using an Ethernet crossover cable) communications can be established using a standard SNMP manager software package.
The fault LED is a tri-color LED . When the unit is first powered ON, the Fault LED should momentarily be RED, then after initial memory checks have been successfully completed the Fault LED should turn to ORANGE while further initialization of the unit takes place. If the Fault LED remains RED, this indicates a catastrophic failure in the unit, and the unit should be returned to the factory for repair.
The Fault LED will remain ORANGE during preliminary initialization of the unit, before moving on to initialization of the internal GPS module, when the Fault LED will remain on but the GREEN Lock LED will begin to flash.
Also, after successful initialization, the Fault LED will illuminate ORANGE and the Lock LED will be OFF if the unit goes into the "holdover" mode.
In order to determine whether the unit has initialized, the serial or Telnet pots can be used to more fully determine unit status.
Once preliminary initialization is completed, the unit will move on to initialize the internal GPS engine (if the input source, command A15, is selected as GPS). When the unit goes into the GPS initialization mode, the fault LED will remain ON, and the green Lock LED will flash on and off. The length of time the unit remains in this mode will depend on a variety of factors, including whether the unit is in fixed position mode or survey mode (menu command A05), how many position averages (menu command A01) are required if in survey mode, how many satellites are in view etc. If there is a set up problem (i.e. the antenna cable is shorted, or insufficient satellites in view) the unit will remain in this mode until the problem is cleared.
Following initialization of the internal GPS engine, the fault LED will extinguish, but the Lock LED will continue to flash (unless the unit contains an internal Rubidium atomic clock, in which case the Lock LED will immediately illuminate). This indicates that the unit has moved on to the next phase of initialization, which is to lock the internal oscillator to the incoming GPS signal, using the Phase Lock Loop "fast" mode. Dependent upon oscillator type, and how many "in range" samples have been preset, and also how many GPS satellites are in view (the unit will not take measurements while there are insufficient satellites to provide a good incoming GPS signal) this can take a varying amount of time.
This is a normal mode of operation when the unit goes into the "holdover" mode. Holdover is caused by loss of a reliable input signal, usually due to insufficient viewable satellites (or if the Ext In 1 mode is selected, loss of input 1PPS signal), or possibly a problem with the antenna cable. The unit will continue to provide a good output, with an accuracy dependent upon the type of internal oscillator fitted and the length of time the unit remains in holdover. Once view of satellites is restored, the unit will revert to normal operation. The green Lock LED will not illuminate until the unit has taken sufficient good samples to recover the phase lock loop.
There are several modes of operation of the time display, either on the front panel display (if fitted) or the remote time commands, with he exception of the NTP protocol that is always transmitted as UTC (Universal Time Coordinated, the international time standard).
The modes of time output display are;
GPS time display is simply UTC with a difference of the number of leap seconds since 24:00:00 on January 5, 1980 (the commencement of GPS time), which in 2006 are currently 14 leap seconds. Therefore GPS time will be ahead of UTC time by 14 seconds.
Local time is dependent upon the unit time settings. To display a correct local time, the local time offset from UTC must be entered (menu command A07). The local time offset is the time zone difference between local time and GPS. For US Eastern Time the value to be entered is –50 (which represents –5 hours behind UTC). The next parameter is daylight savings time (menu commands A08 and A09). Currently this is only implemented for the USA and the UK. For other locations, the time offset must be adjusted accordingly, dependent on the time of year.
If the IRIG B time code output is being used from the rear of th unit, the time output will be the same as the time display settings.
In order to provide accurate time, the unit must first be set to, or acquire, accurate position. For first ime initialization, this is usually done by using the "survey' mode (menu command A05) so that the unit automatically acquires accurate position during initialization. Survey mode requires a minimum of 4 satellites in view to complete the initialization. After first time initialization, position will be remembered and the unit can be set to 'fixed' position mode which will enable a faster initialization as only one satellite needs to be tracked to set accurate time.
If the unit is then moved it is necessary to re-survey the position, as at a minimum there will be an inaccuracy in the time signal, and in the worst case, where the unit is moved many kilometers, the unit will not be able to locate the expected satellites and will not complete the GPS lock initialization.
The normal default mode for the unit has GPS selected as the source for the 1PPS input (menu command A15). In this mode there are three phases of initialization;
During this phase, the unit is setting the internal ports, establishing the Ethernet port and serial port communications and several other set up functions to set the basic functionality of the unit.
The Power and Fault LED's will be ON and the Lock LED will be off during this phase.
During this second phase initialization the internal GPS engine will acquire satellites and establish an accurate position needed for accurate time. This phase can take a variable amount of time dependent upon satellite visibility.
During this phase the Power and Fault LED's will be ON, ad the Lock LED will be flashing.
Once the internal GPS engine has acquired satellites and locked, the unit will move onto the third stage of initialization, which is to lock the unit 1PPS output to the incoming GPS 1PPS signal. Depending on the type of oscillator fitted (TCXO or OCXO) this can again take a variable amount of time. If the unit has a Rubidium internal oscillator this phase is not required.
During this phase, the Lock LED will be flashing, the Power LED will be ON, and the Fault LED will be off.
If the unit is to be used with an External 1PPS signal (e.g. a cesium standard) as the reference instead of GPS, it is necessary to set the unit into the Ext In 1 position instead of GPS (menu command A15).
Once the mode has been set to Ext In 1 (menu command A15), it is then necessary to reset the unit by removing and then reconnecting the AC input power. The unit will then skip unnecessary initialization stages.