Page 7
8.0 OPTIONS
The rear-panel of the ES-185U provides access to all "Optional" inputs and outputs via various connectors (BNC
and DB-9). Please refer to section 9 for more details.
ANT: A high performance antenna for challenging EMI environments is provided with this option. Nineteen
feet of cable is supplied with the antenna. An N-Connector (jack style) is supplied on the antenna. The
cable is supplied with a mating N-Connector and a TNC to connect to the ES-185U.
Clear: When this option is specified, the ES-185U is supplied with a clear anodized front panel.
DC: The ES-185U can be ordered from the factory to operate exclusively from a DC source. Two versions
of this option are available, 12 VDC and 28 VDC. The range for the 12 VDC is +10 VDC to +16 VDC
and the range of the 28 VDC is +20 to +34 VDC. The DC voltage applied to the unit is via the Locking
DC Power Plug. Note: When the DC Option is specified, the unit is NOT operable from AC. Also, at
time of order, either 12 or 28 must be specified.
HR: Option "HR" provides a user programmable relay contact closure. Refer to section 5.3 for information
on setting the times of up to four programmable relay closures. The reed relay is rated at 10 watts
maximum resistive load (500 mA switching current) and is intended for control applications only. The
relay contacts are accessible on the DB-9 connector (see section 9 for pin designations).
J: The standard ES-185U is intended to operate from 117 VAC 50/60 Hz. If 220 VAC operation is
required, Option "J" must be specified.
K: Option "K" provides a 1 KHz square wave, a 10 MHz sine wave and a phase coherent 1 PPS output.
The 1 PPS output has a 50% duty cycle and replaces the standard 50% duty cycle 1 PPS output. The
1 KHz and 10 MHz outputs are accessible on BNC connectors. The 10 MHz sine wave is 4 Vpp into
50 ohms. Potentiometer R6 allows the output level of the sine wave to be adjusted by +/- 0.5 volts.
The 1 KHz square wave is 5 Vpp. A front panel 10 MHz Lock LED is provided. This LED lights solid to
indicate that the unit has “locked” to GPS and the outputs are within specifications. The 1 PPS output
is phase coherent when the 10 MHz Lock LED lights solid. The LED blinks if GPS “lock” has been
obtained, but the outputs are out of specifications. If “lock” has not been obtained, the LED does not
light.
The Option “K” system functions independently from the rest of the clock, although it receives its input
from the same GPS receiver as the clock system. When first powered up, the receiver searches for
satellites. When it locks on to at least one, the GPS Lock LED indicates a locked condition by lighting
solidly. The 10 MHz Lock LED begins flashing after a delay of about 40 seconds. The flashing of this
LED indicates that the GPS receiver is locked and that the 10 MHz system is in the process of
adjusting the frequency of the 10 MHz output. This process may take up to 1 hour. During this time the
frequency, if measured, may indicate 100 – 200 Hz off. This is normal during the locking process.
While the 10 MHz Lock LED is flashing, the output should not be used as a reference. When this LED
lights solidly, the output is within tolerance.
The ES-110M12 PCB generates the Option “K” outputs – 10 MHz & 1 KHz. The PCB receives 1 Hz
and satellite data from the GPS receiver on the main PCB. +12v & +5v power is also supplied to the
110M12 board. The system consists of a TCXO (temperature-compensated crystal oscillator), counter
chain, phase detector, loop filter and supervisory microcontroller (Z2). The 20 MHz oscillator is divided
by the counter chain (Z7-Z12 & part of Z5) down to 1 Hz. The phase-detector chip (Z4) receives this
signal and the 1 Hz signal from the GPS receiver. Z4 produces an output which is fed to the loop filter,
consisting of analog switch Z3, resistors R15 - R17, capacitors C22 - C23 and op-amp Z17. The
analog switch allows the microcontroller to control the time constant of the filter and also disable the
loop during periods of non-reception of satellites. The filtered control voltage is fed to the frequency
control input of the TCXO. This functions as a phase locked loop, controlling the frequency and phase
of the oscillator from the GPS reference 1 Hz. The satellite data from the GPS is fed to the
microcontroller UART input, allowing the system to know if the receiver is locked to satellites. The
microcontroller also monitors an output from the phase detector chip to determine the amount of
phase difference between the GPS and the internally divided 1Hz. If it is greater than approximately 40
milliseconds, the microcontroller “gear shifts” the counter chain fast or slow to bring the relative phase
to under 40 mS. This procedure is performed during initial lock-on, or if reception of satellites is lost for
a significant time and enough drift occurs. After rough phase adjustment is performed, the oscillator
frequency remains either fast or slow by about 100-200 Hz until the local 1 Hz arrives in phase with
the GPS 1 Hz. This typically takes up to 1 hour. During this time, the 10 MHz Lock LED flashes. The
frequency then stabilizes at the center frequency of 20 MHz (it is divided by 2 for the output). After
