The tools below have been implemented in Mathcad 8 Pro, available from Mathsoft, Inc. The html or pdf versions can be viewed, but interaction with the worksheet is not possible. For that, download the mathcad worksheet form, but then you will need Mathcad 8 to view or use the file. Please note that neither NRAO or I guarantee the correctness of these worksheets, although to the best of my knowledge they give results consistant with those of the underlying papers or data.
Calculation of conducted heat loads through metal or other materials is often necessary in the design of cryogenic receivers. Two mathcad worksheets are provided for assistance in this work:
In the January 1956 Proceedings of the IRE, R. W. Klopfenstein presented equations which can be used to design transmission line tapers. "...the Dolph-Tchebycheff taper is optimum in the sense that it has minimum reflection coefficient magnitude in the passband for a specified length of taper". One drawback of the Klopenstein taper is that an impedance discontinuity or step occurs at the ends of the taper. The Klopfenstein worksheet may be viewed in html format, or downloaded in Mathcad Worksheet format (zipped).
In the November 1972 Transactions of the MTT, R. P. Hecken modified the Klopfenstein methodology to eliminate the impedance discontinuities. This "near-optimum" taper is only slightly longer than the Klopfenstein taper. The Hecken worksheet may be viewed in html format, or downloaded in Mathcad Worksheet format (zipped).
Many NRAO receivers, including those on the VLBA and those built for the GBT, use a Teledyne-Hastings DV-6 thermocouple gauge tube for vacuum sensors. A "sensor card", designed by S. Weinreb, drives these tubes and produces a voltage output for display and input to monitoring computers. The voltage is a non-linear function of the pressure, and it is sometimes desirable to convert the voltage reading to a value in units of pressure. The worksheet used to produce a mathematical fit to the DV6 vacuum sensor output may be viewed in html format, or downloaded in Mathcad Worksheet format (zipped).
The Tchebyschev filter response is the most common model used in microwave filters. The worksheet Tcheby.mcd uses analytical equations to calculate ideal filter responses as a function of passband ripple and number of poles. Equations for mapping lowpass prototypes to bandpass responses are also given. The worksheet may be viewed in html format. The worksheet TchebyQuarterStub.mcd is an extension, providing synthesis equations for a distributed filter topology using series and shunt quarter-wave stubs. The worksheet may be viewed in html format. Both worksheets may be downloaded in Mathcad Worksheet format (zipped).