Crystal Mixer Research Articles

The limitation of the dynamic range of a spectrum analyzer due to nonlinear processes in the mixer

Theoretical formulas are obtained for estimating the relative levels of spurious “responses” of the output of a spectrum analyzer when the useful signal voltage, the heterodyne voltage, and interference simultaneously act at the input of the crystal mixer.

A multipurpose efficient tunable infrared coherent source with tuning range from 0.8 to 25 μm and peak powers in the range 50–200 kw

We have developed in the last 2 years a multipurpose efficient tunable coherent source in the near- and mid-infrared, with high level beam quality and stability requirements. This complex device makes use of a high reliability home-made YAG: Nd 3+ laser as primary power source, associated with a 1.06 μm pumped infrared dye laser (i.r. dye), a lithium niobate optical parametric oscillator (OPO), two optical mixer crystals, gallium selenide (GaSe) and cadmium selenide (CdSe) and a lithium niobate doubler. At the present time, the following wavelength ranges have been covered: 1.08–1.20 μm and 9–19 μm starting from the i.r. dye, and 1.6–3.6 μm, 0.8–1.8 μm and 2.6–25 μm starting from the OPO. According to the wavelength the peak powers extend from 50 W to 200 kW.

Wavelength-tunable optical mixing experiments between 208 nm and 259 nm

Sum-frequency generation experiments in which the second harmonics of rhodamine and coumarin dye lasers are upconverted to the 208-234 nm by mixing with 1064 nm are described. The dye lasers were pumped by the second and third harmonics of a repetitively pulsed Nd:YAG laser. Both temperature-tuned and angle-tuned phase matching techniques were used with mixer crystals of ammonium dihydrogen phosphate (ADP) and potassium dihydrogen phosphate (KDP). Tunable light from 246 nm to 259 nm also was generated by mixing the output of a coumarin laser with the 532-nm harmonic of the Nd:YAG laser. Peak powers between about 500 W and 10 kW were obtained, and both theoretical and experimental tuning curves have been determined for these processes. Limitations imposed by mode beating effects in the Nd:YAG laser and by the relatively broad linewidth of the dye lasers are discussed.

Far-infrared generation from a spin-flip laser

Far-infrared emission has been observed from an InSb spin-flip Raman laser where a mode-locked TEA CO2 laser is used as the pump source. 400 μW of power are generated in 2-nsec pulses near 100 μm. This contrasts with the usual two-crystal scheme where one crystal is used to generate the Raman Stokes signal and a second InSb crystal is used as a mixer crystal. This experimental simplification allows for a much more direct evaluation of the usefulness of the spin-flip Raman laser as a source of far-infrared radiation. It is concluded that current technology permits construction of a spin-flip Raman far-infrared spectrometer tunable over about 60–125 cm−1.

Diode Mixer Coefficients for Spurious Response Prediction

The precise prediction of spurious response levels in a superheterodyne receiver would greatly aid the receiver designer besides being necessary for the representation of a radio frequency interference environment. The power series is used to represent the nonlinear receiver mixer in order to obtain an expression for the receiver spurious response sensitivity. This sensitivity expression contains the power series coefficients and shows that the coefficient magnitudes must be known before the spurious response levels can be computed. Therefore, a method is developed to provide a solution for the power series coefficients of a typical mixer circuit configuration. In the analysis to determine the coefficients, the input voltage-output current loop equation is written for a crystal mixer equivalent circuit. This expression is expanded in a power series and then the reversion of a series technique is implemented to obtain the desired output-input expression in series form. The effects of the nonlinear element (diode) and the total circuit resistance are included in the results. Coefficient expressions are determined up to the ninth order in the manner described above and the level of each expression is computed versus the product α( IR + Iß) RT where α and IR are diode parameters, RT is the equivalent circuit resistance, and Iß, is the dc bias current. Also, the effect of diode bias upon spurious response sensitivity is considered and the results are plotted. The results show the mixer dc operating conditions which must exist in order to reduce spurious response sensitivity.

Graphical Presentation of Spurious Responses in Tunable Superheterodyne Receivers

The theory of intermodulation responses in superheterodyne receivers is briefly reviewed. The frequency bands of the responses are determined and factors affecting susceptibility levels as well as quantitative values for a typical crystal mixer input superheterodyne receiver are presented. On the basis of this groundwork, it is shown that the receiver's primary and spurious responses may be conveniently presented in graphical form. The graphical presentation can include the effects of input band-pass filters and tunable preselectors, and provides a grid upon which an electromagnetic environment may be superimposed.

1414 Mc/sec Jupiter observations

view Abstract Citations (3) References (7) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS 1414 Mc/sec Jupiter observations Miller, A. C. ; Griffin, J. Abstract Jupiter was observed at a frequency of 1414 Mc/sec on 28 nights from 10 September to 17 December 1963 using a crystal mixer receiver with a linearly polarized rotating feed horn installed in NRL's 84-ft radio telescope. Rotating feed measurements gave, for 244 rotations, an average equivalent blackbody tempera- ture of 2590 + (s.e.) and a fractional polarization of 0.23+0.03 (s.e.) at an average position angle of 61?0+2?0 (s.e.) for the maximum intensity. The average of 241 drift curves taken with the E plane of the feed horn oriented at the position angle of the Jovian optical equator gave a temperature of 3250+ (s.e.). Observed equatorial and polar fluxes of 5.5 and 3.4X 10-2 W cps-', normalized to 5 a.u., agree within +0.2 flux units with previous NRL measurements made near 1400 Mc/sec. The temperatures and fluxes are based on an assumed value for Virgo A of 198 X 10-20 (mks). Publication: The Astronomical Journal Pub Date: October 1966 DOI: 10.1086/110181 Bibcode: 1966AJ.....71..744M full text sources ADS |

The backward-wave converter, an electronically swept receiver

The backward-wave converter is a hybrid device that combines the essential elements of an electronically swept receiver front end in a single vacuum envelope. The device directly converts an RF signal to an IF signal with the mixing processes taking place in an electron beam. The tuning is completely electronic, and octave frequency coverage has been achieved. Compared to the conventional crystal mixer system the device provides a number of advantages such as 1) elimination of crystal burnout, 2) isolation of local oscillator power from the antenna, 3) preselection and 4) voltage tunability at high rates of speed over a large frequency range. A theoretical analysis that compares satisfactorily with experimental data has been developed.

Image-frequency effects in a microwave crystal mixer

An investigation of the properties of an image-reflection microwave mixer is described. Experimental results are presented which show an improvement in conversion loss and noise figure over the image-absorption mixer. In general, the optimum image termination is an open circuit. The output of the mixer at image frequency is investigated and the condition for zero image output is established. It is shown that image output is strongly dependent on i.f. load. When operated in the region of low image output the mixer is insensitive to image termination, and the increase in noise factor is small. Measurements show that reciprocity holds for the CV2154 mixer. In general, good agreement is obtained between theoretical and experimental results.

Image power in a microwave crystal mixer

An investigation of the output of a microwave crystal mixer at image frequency is described. A curve is presented showing the dependence of image output on i.f. termination. This curve indicates an operating region where mixer performance is insensitive to image termination.

Intermodulation analysis of crystal mixer

An expression for the amplitude of the intermodulation products and harmonics produced in a crystal mixer is derived using the coefficients of the power series expansion of the device. Using this expression and an exponential approximation of the current through a diode [i = i 0 (eαv- 1)], the amplitude of intermodulation produced in a crystal mixer is found to be 2i 0 eαV0R 0 I s (αV 1 )I b (αV 2 ). I n (x) is an nth order modified Bessel function of the first kind. The quantities s and b are the signal harmonic and the oscillator harmonic, R 0 is the output resistance, and V 0 , V 1 , and V 2 are the bias, signal, and oscillator voltages, respectively. The quantities i 0 , α, R 0 , and V 2 are found from the dc E-I diode characteristics, the mixer bias current, and the loss in the desired signal. Experimental tests on a mixer operating from 450 Mc to 850 Mc show that the signal input power necessary to produce a given intermodulation output power can be predicted within 6 db.

Superheterodyne radiometers for short millimetre wavelengths

Millimetre-wave radiometers suitable for making temperature measurements on plasmas are discussed. After a brief review of radiometer theory, special attention is paid to the design of the low-frequency radiometer circuits, the performance of mixer and harmonic-mixer crystals at short millimetre wavelengths, the local-oscillator power needed and the suppression of local-oscillator noise and spurious signals.An early 140-Gc/s radiometer, with second-harmonic mixing and an overall noise factor of 25dB, is mentioned, and a detailed description is then given of a recent 140Gc/s radiometer which contains: a fundamental local oscillator, VX3352 mixer crystals and a 408Mc/s i.f. amplifier commencing with an Adler tube. An overall noise factor of 19dB has been achieved with this equipment and its performance is fully discussed. Some typical recordings of the 2mm radiation from an argon noise tube and Zeta are included.Various ways of obtaining improved radiometer performance at millimetre wavelengths are mentioned. The appendixes are devoted to radiometer theory and an analysis of the halfwave commutator detector.

Superheterodyne Radiometers for Use at 70 Gc and 140 Gc

In this paper four different millimeter wave equipments, which have been made for plasma diagnostic work, are described. They are: 1) A straightforward 70-Gc superheterodyne radiometer with an over-all noise factor of 13 db; 2) An early 140-Gc radiometer, with second harmonic mixing, which has an over-all noise factor of about 25 db; 3) A later and more sensitive 140-Gc radiometer which contains a fundamental local oscillator, VX 3352 mixer crystals and a 408-Mc IF amplifier commencing with an Adler tube; 4) A very simple 140-Gc transmission measuring equipment containing a 1-watt source and a crystal video receiver which has a tangential sensitivity of ---42 dbm. The last part of this paper discusses the minimum temperature changes which can be detected, at short millimeter wavelengths, with various types of superheterodyne radiometers, the Golay cell, the barretter, the crystal video radiometer, the 1.5/spl deg/K carbon bolometer and the 1.5/spl deg/K InSb photoconductive detector. The performances expected from straight traveling-wave tube radiometers and traveling-wave masers at short millimeter wavelengths are also considered. The Appendices are devoted to mixer crystal performance in the millimeter and submillimeter regions, a theory of second harmonic mixing and the voltage sensitivity of a forward biased detector crystal.

The backward wave converter

This paper describes the development of a backward wave converter which is a hybrid device that combines the essential elements of an electronically swept receiver in a single vacuum envelope. Early work at ITTL was undertaken on the development of an electronically swept receiver which used a backward wave amplifier, a backward wave oscillator and a crystal mixer. Near the end of this development, work was reported by Gray of the University of California on the possibility of combining these three functions in a single vacuum envelope. Encouraged by the success in tracking the two backward wave tubes to provide a constant I-F in the receiver development, we undertook the development of a backward wave converter, as the device was called, for the frequency range of 500 to 1000 Mc. This device provides a number of advantages when compared to the conventional crystal mixer, such as, (1.) Elimination of crystal burnout, (2.) Isolation of L. O. power from the antenna, (3.) Preselection, (4.) Voltage tunability at high rates over a large frequency range. These early backward wave converters, which could be swept at rates up to 1 kc over an octave band, had a preselection bandwith of 10 mc, a dynamic range of greater than 70 db and an I-F output at 60 inc. Noise figures, when the tube was adjusted for octave tuning operation, ranged between 13 and 19 db. Much better noise figures than this (6-8 db) could be obtained at spot frequencies by optimizing the voltage profile between cathode and helix. Limitations of length required the use of higher beam current (6-10 mA) than is desirable for good low noise performance. Thus if these limitations are removed a considerable improvement can be expected. A range of converters are now being developed extending to the 12 Gc region. Results on these later tubes will be given. Possibilities and expectations of extending this technique to the mm wave region will also be reviewed.

A hall-effect microwave mixer

The paper describes the theory and performance of a new microwave mixer based on the fact that the Hall electric field produced at any point in a semiconductor is dependent on the vector product of the current density and the magnetic field applied at that point. This mixer stage behaves differently from the more conventional forms in that the output contains only components of the local-oscillator and signal frequencies.Two designs of Hall-effect mixer were developed, and their conversion properties were experimentally investigated at about 10Gc/s. The best value achieved for the conversion loss was 57 dB with a local oscillator power of 10W and using a semiconducting film of indium antimonide having a Hall mobility of 0.173m/s per V/m. It should be possible to improve the efficiency of this mixer by using higher-mobility films and higher power for the local oscillator, and by operating the device at low temperatures.Besides being a linear device, the Hall-effect mixer has a power-handling capacity which is much larger than that of the ordinary crystal mixer. Moreover, the technique used offers a useful method for measuring the Hall mobilities of carriers in semiconductors at microwave frequencies.New information is also given about a technique for the preparation of evaporated indium-antimonide films which proved to have a Hall mobility as high as one-fifth of the material in bulk.

Measurement of the Conversion Conductance of Esaki Mixer Diodes (Correspondence)

In order to compare the theoretically predicted and the experimentally observed behavior of frequency converters using Esaki diodes, it is necessary to evaluate various mixer parameters, in particular, the conductance elements of the conversion matrix. It is well known, these conductance elements are certain Fourier coefficients of the periodic series representing the incremental time-varying diode conductance. This conductance is produced by the large local oscillator (LO) voltage acting on the non-linear diode. Although one can determine these element values using a numerical Fourier analysis, this approach is both time-consuming and laborious. As an alternative, we suggest an experimental technique originally proposed by Dicke over ten years ago for use with conventional (positive-conductance) crystal mixer diodes. Since this method is quite easy to apply in that it only involves several low-frequency bridge measurements and one standing-wave measurement, and since, apparently, it is not well known, we shall risk repetition by describing a simplified version of it which we have modified to apply to Esaki diodes.

A Note on the Optimum Source Conductance of Crystal Mixers

This paper describes an accurate and convenient technique for measuring the match of a crystal mixer. Use is made of the fact that with a proper RF drive level, the fundamental conductance of a mixer crystal may be made equal to the optimum source conductance of the crystal for mixer operation, The required drive level depends on certain crystal parameters and on the image frequency termination of the mixer. Design curves are given which simplify the determination of the proper RF drive level for a wide range of crystal parameters and their condition of image frequency termination.

A STUDY OF CENTAURUS A AT 31 CENTIMETERS

covered, and shortly after its discovery it was identified with the peculiar galaxy NGC 5128. Interferometry by Mills1 showed that there was a central source of dimensions 6' X 3', and Bolton, Westfold, Stanley, and Slee2 found that there was an associated extended source of dimensions of the order of 2°. The extended object was also observed at 400 Mc/s by McGee, Slee, and Stanley, with a pencil-beam antenna,3 and by Piddington and Trent at 600 Mc/s.4 The latter investigators suggested that the extension might form a bridge between NGC 5128 and our own galaxy. The true extent of this object has only really become apparent since the studies by Sheridan5 with the 85 Mc/s Mills cross (beam width 50') and by Shain6 with the 19.7 Mc/s Mills cross (beam width 1?4). These observations show an elongated object nearly 10° in length lying almost along a line of constant right ascension. The present study was carried out with a 90-foot equatorially mounted radio telescope at a frequency of 960 Mc/s. At this wavelength the beam width is about 50 minutes of arc. The receiver used had a conventional crystal mixer with an excess noise temperature of about 300° K. No image rejection was employed ; thus the signal was received in two bands at 930 and 990 Mc/s, each 10 Mc/s wide. The receiver input was switched at 400 cycles per second with a diode switch between the main horn feed pointed at the reflector and a reference horn directed away from the reflector. The 400 cycles per second difference signal was recorded. The observations consisted of a series of drift curves taken with the telescope fixed on a particular declination. Due to the low altitude of this object, only three observations (at different hour angles), each lasting about 40 minutes, were made on each night. One of these was for calibration purposes at declination 42°40'. The maximum signal received from the direction of the central source corresponded to an antenna temperature of 50° K, but the

Radar crystal valves

A brief historical survey is made of the use of semiconductor devices as frequency changers or mixers in radar applications, with particular reference to factors that led to the design and performance of the types CV2154-5 silicon mixer crystals. The factors that led to the choice of a coaxial construction and the part played by the insulator and its effect on admittance is discussed. A mixer crystal incorporating a germanium wafer and titanium whisker is described. This crystal has a noise factor better by 2 dB than the silicon and tungsten combination of the types CV2154-5.The necessity for positive bias, its effects on r.f. admittance and noise factor and methods of obtaining the bias when required are considered. The superior bandwidth and small spread in admittance between samples is attributed to the choice of material for the insulator. Burn-out performance is discussed and measurement of this parameter indicated.Finally, it is shown that, contrary to general belief, the behaviour of germanium mixer crystals as a function of temperature is not significantly different from silicon devices, at least over the temperature range −80 to + 100°C.

The germanium microwave crystal rectifier

The characteristics of the commercial germanium microwave mixer crystal are reviewed. The conventional theory for these devices is discussed and criticized on the grounds that minority carrier storage phenomena are completely ignored. A model which includes this effect is proposed, and conversion loss calculations which include the effect of spreading resistance are presented for a highly idealized version of this model. Some possible explanations for the dc characteristics and for the success of the conventional fabrication techniques are offered.