|Our model SQE-RF-3G is an ac-flux modulated rf SQUID readout circuit
with a modulation frequency of 400 kHz. Other rf and modulation
frequencies are available on request. The electronics features a
low-noise preamplifier with a noise temperature of about 80K at 3GHz.
Due to the ac-flux modulation, drift and low-frequency excess noise caused
by temperature fluctuations are supressed. The SQUID readout measures
160 mm by 85 mm by 35 mm. As it is small and light, it can be placed
close to the SQUID.
This SQUID readout is ideally suited for measurements at lower signal
frequencies, such as noise thermometry, gravity-wave or geophysical experiments,
or biomagnetic measurements.
The SQUID readout circuit is controlled by our control box SQC-1, which
can be placed several meters away from the readout. This control
box is used to set the rf SQUID frequency and rf power to the SQUID, the
flux-modulation amplitude, the phase shift between modulation and internal
lock-in reference, and the feedback resistor. The actual parameters
are displayed on a illuminated LCD display and can be changed manually,
or by a personal computer via the serial port. A personal computer,
however, is not required to operate the SQUID readout. The internal
microcontroller of the control box can be switched off when performing
extremely sensitive measurements. The parameters for 20 different
SQUIDs can be stored internally, and can be recalled when the same device
is being used the next time. The box can either be battery operated
(at any dc voltage between 18 and 24 volts) or supplied from a mains-operated
power supply. The current consumption is about 250 mA (display on),
or 200 mA (display off). The SQUID readout is supplied with power
from the control box. The SQUID readout can also be supplied with
a built-in rechargable battery allowing for a measuring time of 4 to 8
hours (in a larger box, see the picture of our SQE-DC-BR-400k below).