User Manual
16
UM-20 Low-cost Oven-controlled Crystal Oscillator (OCXO) Assembly
Use in XL Microwave Model 3xxx
Installation
As a test, we decided to install the assembled OCXO module with
OCXO131-40 S/N 2140-624 into an XL Microwave Model 3030
frequency counter.
Both the upper and lower covers of a Model 3xxx must be
removed in order to access the screws that hold the oscillator
assembly in place. Four 4-40 x 3/16” flathead screws hold the
OCXO assembly in place, and
J1
is connected to a single
connector labeled 10 MHz BUFFER on a nearby PCB.
Figure 6: OCXO PCB assembly installed in Model 3xxx
Frequency Tuning
It turns out that the initial values of 15k
Ω
for
R6
and
R8
restricted
the VCO trim range too much
on this particular unit
to be able to
reach 10.000000MHz. Replacing
R6
and
R8
with zero-Ohm
resistors yielded a
V_TRIM
(
TP3
) of 2.73Vdc to reach
10.000000MHz.
With zero-Ohm
R6
and
R8
, the trim range of the VCO (stated by
IsoTemp to be up to 0.9ppm or 9Hz over the full range) required a
full ±2.5V of
V_TRIM
at the VCO input with
R7
= 1k
Ω
. To reach a
multi-turn trimpot for
setting V_TRIM
22AWG 0.100” pitch
harness connector to
Model 3xxx 10MHz
oscillator stage
Содержание UM-20
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