|For applications requiring a large dynamic range at relatively high
signal frequencies, we offer SQUID readouts with ac-flux modulation frequencies
between 1 MHz and 25 MHz. The standard model is our readout SQE 4
M. It is an ac-flux modulated dc SQUID electronics with a modulation
frequency of 4 MHz, which we also employ in our NDE systems. The
preamplifier has a noise temperature of less than 15 K (typically 10 K
for a source impedance of 20 ohms). The bias current for the SQUID,
the preamplifier gain, the modulation amplitude and the phase between modulation
and internal lock-in reference can be adjusted. Eight different feedback
resistors can be selected. With a good niobium SQUID, a dynamic range
of up to ten flux quanta can be achieved at frequencies above 100 kHz.
The SQUID readout can be controlled by our control box SQC-1. The
SQUD readout measures 165 mm by 110 mm by 40 mm.