Model A3-R Operation And Service Manual
A3-R Manual 14 May 2002
Page 5 of 6
Model A3-R Quartz Frequency Standard
Introduction
The Model 3 quartz frequency standard is based upon a new design of oven – controlled
crystal oscillator and will give excellent service over long time periods. The unit is fed from an
internal, switched – mode power supply working at 50/60 Hz and supplied from a mains source of
between 110 V and 240 V (r.m.s.).
Front Panel
The front panel is fitted with a green “power on” light – emitting diode indicator on the right – hand
side.
Back Panel
R.F. Output
The back panel is fitted with a B.N.C. socket giving a 10 MHz reference output, a at level of
approxi10 dBm (50
Ω
). This is suitable for distributing around laboratories, workbenches
etc through a distribution amplifier.
Very Long – Term Frequency Adjustments
On leaving the factory the unit will have been adjusted against a hydrogen maser frequency
standard, to within one part in 10
11
.
However, it is appreciated that quartz crystal oscillators will tend to drift (upwards) in
frequency over long time periods, due to crystal ageing. Should the customer consider that the drift
eventually renders the unit in need of correction, the following should be carried out:
EITHER Return the unit to Quartzlock for re – adjustment against the hydrogen maser there
OR If a high accuracy frequency standard is locally available, remove the six lid –
retaining screws and locate the blue, 10 kR, 20 turn potentiometer, next to the OCXO unit.
Very carefully adjust this potentiometer until the frequency is within acceptable limits. A
comparison frequency standard, whose accuracy is better than one part in 10E-12, is recommended
for this adjustment.
Internal Switched-Mode Power Supply
WARNING: Risk of electrical shock or burns
Capacitors store hazardous energy
Do not touch the power supply until after 5 minutes after disconnecting the mains
Pin Connections
1.
AC(L)
Input terminal live
2.
AC(N)
Input terminal neutral
3.
FG
Field Ground (Protective Earth)
4.
+ Vout
Output terminal VCC
5.
- Vout
Output terminal GND
6.
Vadj.
Output voltage adjustment potentiometer
