User Manual
UM-20 Low-cost Oven-controlled Crystal Oscillator (OCXO) Assembly
17
V_TRIM
of 2.76Vdc required
R6
and
R8
values of under 5k
Ω
; 1k
Ω
resistors were eventually fitted.
R6
&
R8
Values
V_TRIM
Range
Notes
0
Ω
±
2.50V
Entire range yields changes in output frequency of
± 6.27Hz, or around 0.6ppm (within specs).
OCXO131-44 S/N 2140-618 output was
9,999,993.55Hz @
V_TRIM
= 0.00Vdc, and
10,000,006.87Hz @
V_TRIM
= 5.00Vdc.
1k
Ω
±
0.83V
S/Ns
1946-88, 2302-1000, 2140-624 & 4231-0013
were trimmed with these values.
2k
Ω
±
0.50V
5k
Ω
±
0.23V
10k
Ω
±
0.12V
15k
Ω
± 0.08V
S/N 2140-618 was trimmed with these values.
Table 5: OCXO131-40 frequency tuning range as a
function of
R6
&
R8
Realistically, the choice for
R6
&
R8
boils down to 0
Ω
(guaranteeing the greatest possible frequency tuning range) or 1k
Ω
(giving a tuning sensitivity that’s 3x greater that that of the 0
Ω
configuration, but with less frequency tuning). Values greater than
2k
Ω
for
R6
and
R8
are likely to prevent trimming to
10.000000MHz, unless the initial
V_TRIM
is within roughly
100mV of 2.5V.
Note
Different values for
R6
and
R8
could be used on a case-by-
case basis to optimize the trim range for a given OCXO131-40.
In-place Tuning
The lower cover of the Model 3xxx must be removed in order to
trim the installed OCXO assembly to 10.000000MHz. This
requires that the Model 3xxx be upside-down when adjusting the
OCXO frequency.
8
8
A carefully positioned hole could be drilled in the lower cover of the Model 3xxx,
to gain access to the PCB assembly’s trimpot without removing the lower
cover.
Summary of Contents for UM-20
Page 28: ...W J o on O O O m 5 0 u G O O O O O Omwmww 3 O f 0 016679 Lager 1 TOP ...
Page 29: ...016676 Lager 1 2121 ...
Page 31: ...016676 Bottom Soldermask ...
Page 81: ......
Page 82: ......