MOGlabs DLC202, Manual, Page: 59 / 82

C.3 Impedance matching 49
The
MOG
labs
DLC
operates at ω = 250 kHz. For a cell of length
8 cm, 0.4 mm wire, and 20 mA, we find L
Wheeler
≈ 650 µ H, and
ε
m
ax
= 20 V, and the maximum slew rate is 32 V /µ s.
The
MOG
labs
DLC
does not have that direct output capability. Re-
ducing n helps: inductance, and thus ε and dV /dt fall with n
2
while
the frequency modulation depth falls with n . Thus a coil of about 40
turns (500 m
− 1
) and current amplitude of 150 mA should result in a
modulation depth of 1.3 MHz. However, we prefer to use a two-coil
impedance matching arrangement to increase the modulation depth
at smaller currents.
C.3 Impedance matching
The
DLC
can drive up to ± 0 . 5 A and ± 8 V, with a slew rate of 6 V /µ s.
This can be impedance-matched to a high current coil using a trans-
former, or quite effectively by directly winding a primary on the main
Zeeman coil, as shown in the photo above.
For the main Zeeman coil, 0.4 mm to 0.6 mm diameter wire wound
around the vapour cell, about 120 to 200 turns, works well. The coil
is “balanced” for the standard modulation frequency of
ω = 250 kHz
using a capacitor. The coil is excited inductively by a primary, about
five to ten turns, connected directly to the
DLC
modulator output (see
figure). The cell, coils, and balancing capacitor can be conveniently
mounted on a
PCB , as shown in the image above, available from
MOG
labs.
L
C C
Figure C.2: Circuit diagram for Zeeman coil and excitation coil. Typically
the primary is 5 to 10 turns, and the secondary 120 to 200 turns.
The capacitor should be chosen such that the capacitive impedance