MOGlabs DLC202, Manual, Page: 61 / 82

C.5 Shielding 51
Ref -26 dBm Att 5 dB
*
TG -30 dBm
Center 250 kHz Span 500 kHz 50 kHz/
*
*
RBW 1 kHz
VBW 30 kHz
SWT 2.5 s
-120
-110
-100
-90
-80
-70
-60
-50
-40
-30
1
Marker 1 [T1 ]
-41.37 dBm
250.000000000 kHz
Figure C.3: Coil response acquired using a spectrum analyser with track-
ing generator. The response shows a strong resonance near 250 kHz.
C.5 Shielding
Large magnetic fields oscillating at 250 kHz can readily cause prob-
lematic electromagnetic interference (EMI). Induction in the laser
head or the cable to the laser head can easily produce substantial
diode current modulation. The coil (and vapour cell) should be lo-
cated far from the laser and from the controller, or shielded with soft
iron or a high permeability alloy such as mu-metal or Conetic. We
find that a tube made from thin (0.25 mm) sheet mu-metal, about 50%
longer than the cell and coil, is adequate.