Block diagram of the -band spectrometer with Automatic Frequency Control for biological studies in vivo and in vitro.
(Left) Dielectric Resonator-Oscillator based on an bipolar transistor, , (Motorola 3046-type) in a Clapp configuration with a serial resonant circuit in its base. is a single-turn coil that also provides coupling with the dielectric resonator disk, , (Trans-Tech Products 4500 Series Temperature Stable Dielectric Resonator, 30.8 mm diameter, 13.8 mm height) for stabilizing the frequency of oscillation. is a movable dielectric tuning disk, 30.8 mm diameter, 5.0 mm height, driven by an ultrafine-pitch (0.5 mm/turn) screw. is a one-half turn loop providing power output. , , , , , , , . Components marked by asterisks were optimized at assembly time to provide the best performance. (Right) Varactor diode-based system that provides modulation of the output frequency; , .
Diagram of the external-loop type resonator with a circuit allowing maintaining a constant -factor during measurements. This is achieved by intentionally lowering the maximum attainable -factor by coupling in a variable resistance implemented by means of a photoresistor illuminated by an externally controlled light-emitting diode (LED). (Inset) Dependence of the factor for the empty resonator on LED current.
Schematic diagram of a whole-body -band resonator. The whole-body type of resonator has an internal diameter of 30 mm and can accommodate a small mouse. Its construction is based on the bridge-gap concept.
Schematic view of the cross section of the 415 Gauss permanent magnet. 1, Base steel plate; 2, Support column; 3, Ferrite mosaic; 4, Magnet pole; 5, Scan coil.
Schematic diagram of the magnetic modulation unit. Frequency from a 1 MHz clock is divided 40-fold to yield 25 kHz. A four-quadrant selector allows coarse phase adjustment in 90° intervals. The resultant square wave is integrated giving a symmetric sawtooth, which is further converted to a sine wave using an AD639 trigonometric function converter. Following fine phase adjustment the modulation amplitude is set and the modulation current is delivered to the coils via a power amplifier.
4.5 micromole/liter solution of Tempone in 0.9% saline (top, 9 scan average; bottom, single scan). Microwave power 30 mW, receiver gain 10 000, modulation amplitude 0.2 Gauss, scan range 40 Gauss, scan time 20 s, time constant 100 ms.
Parameters of the -band frequency generator.
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