Abstract: The ionospheric delay of a GPS signal transmitted by a first satellite having an obliquity is measured autonomously and substantially in real-time by receiving a code range, a carrier phase range and a satellite elevation angle for each of at least two satellites. For each of the at least two satellites, a code-phase divergence between the code range and the carrier phase range is calculated, an obliquity is calculated from the satellite elevation angle and time derivatives of the code-phase divergence and of the obliquity are calculated. A zenith delay is calculated from the obliquities, the time-derivatives of the obliquities and the time-derivatives of the code-phase divergences of the at least two satellites. The ionospheric delay is calculated by multiplying the obliquity of the first satellite and the zenith delay.

Abstract: An oven assembly for a crystal resonator and oscillator utilizes a thermally symmetrical design to provide a high thermal gain. The oven assembly includes an encasement that forms a hermetically sealed oven chamber that is substantially cylindrical. Concentric with the oven chamber is an annular oven mass that functions as a heat reservoir for the crystal resonator that is contained within the oven mass. The cylindrical oven chamber and the concentric annular oven mass provide two levels of circular symmetry that help achieve a thermally isotropic oscillator environment. Wide-area uniform heat transfer promotes high thermal gain and minimizes thermal gradients. Another factor is the geometry and circuitry for temperature monitoring. Temperature sensors are equidistantly spaced from each other and are equidistant from the center of the oven chamber. Signals from the various thermistors are averaged to provide a more accurate temperature determination for regulating the heaters.

Abstract: The local clocks within each node of a loosely distributed network system may be synchronized and syntonized by any of the nodes in the network. Each of the nodes contains a time packet detector (TPD) that detects and recognizes timing data packets and produces a recognition signal. This signal may be used to cause an action in the detecting node, in particular the node may contain a time service block (TSB) containing a local clock that may be used to record the time of the recognition signal. The recorded times may be used as the basis for correcting the local clocks of the nodes in the system. Transfer devices such as gateways, bridges, and routers may include TSBs and TPDs to allow for correction for the transit time of time packets through the transfer device. The TPD is normally connected within the media access device at the point of final encoding for transmission or recovery of the clock and data for receiving where the time jitter will be at a minimum.

Abstract: A remote receiver for laser interferometer systems is split into two parts connected by a fiber optic link. The front-end of the receiver, located near the remote interferometer optics, houses only the optical components for focusing and mixing the laser beam, and transmits the beam through an optical fiber cable. The back-end of the receiver, located remotely, houses the electronic components for detecting and measuring the frequency difference to produce the signal for the measurement electronics.

Abstract: A circuit for reducing low frequency noise in a direct current biased superconducting quantum interference device. A squarewave bias signal having no dc component is used to bias the two junctions of the dc SQUID. At the same time, the magnetic flux in the SQUID is modulated to heterodyne the input signals up to some convenient frequency where they may be amplified without concern for drift. Final demodulation automatically adjusts for the fact that the relative phase is reversed each time the squarewave bias changes polarity states.

Abstract: A flux locked loop, employing a squid in connection with the production of the locked-loop error signal, includes circuitry which renders the locked loop more immune to disturbance inputs such as a ground-loop noise and interference transients and which facilitates a scale factor adjustment of a sub-carrier drive signal for the squid. To minimize ground-loop noise disturbance effects, a portion of the circuitry in the feedback path of the locked loop includes a voltage-responsive converter circuit arrangement providing a current-drive feedback signal for coupling to the squid. To minimize interference transient disturbance effects, a portion of the circuitry in the forward path of the locked loop includes a circuit arrangement having a non-linear transfer characteristic defining opposed substantial attenuation regions separated by a generally linear gain region.