Online ISSN
1350-911X
Print ISSN
0013-5194
Electronics Letters
Volume 16, Issue 25-26, 4 December 1980
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Volume 16, Issue 25
4 December 1980
Improved orbit utilisation by interferometric sidelobe suppression
- Author(s): M.J.S. van Ommeren ; M.H.A.J. Herben ; J. Arnbak
- Source: Electronics Letters, Volume 16, Issue 25, p. 937 –938
- DOI: 10.1049/el:19800667
- Type: Article
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p.
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–938
(2)
Auxiliary defocused feeds with weak excitation can be used to cancel or reduce specific near-angle sidelobes of double reflector antennas. Existing earth terminals may be upgraded in this way to provide improved isolation between interfering satellites when the tight station-keeping tolerances agreed at WARC-79 come into force.
Compact directional v.h.f. antennas
- Author(s): H.M. Buettner
- Source: Electronics Letters, Volume 16, Issue 25, p. 938 –939
- DOI: 10.1049/el:19800668
- Type: Article
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The prototype of a compact directional antenna for geophysical diagnostics from a borehole has been constructed and tested. The prototype consists of a wire monopole antenna placed next to a ferrite cylinder which loads the antenna thereby changing its characteristics. At its resonant frequency of 230 MHz, the ferrite-loaded antenna has an input resistance of 19 Ω, and is physically shorter by a factor of 2.57 when compared to an unloaded monopole resonant at 230 MHz. The antenna radiation pattern is directional with a front/back ratio of 8.5 dB, and a−3 dB beamwidth of 146° at 249.6 MHz.
Symmetric separate confinement heterostructure lasers with low threshold and narrow beam divergence by m.b.e.
- Author(s): W.T. Tsang
- Source: Electronics Letters, Volume 16, Issue 25, p. 939 –941
- DOI: 10.1049/el:19800669
- Type: Article
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By optimising the layer structure in a symmetric separate confinement heterostructure laser, and by using molecular beam epitaxy to grow the very thin active layer (~500 Å) needed, very low current threshold densities of ~600 Å/cm2 without reflectance mirror coatings and very stable narrow beam divergence of θ⟂~30° and θ∥~4° were reproducibly obtained.
Rotation detection by optical fibre laser gyro with easily introduced phase-difference bias
- Author(s): K. Hotate ; Y. Yoshida ; M. Higashiguchi ; N. Niwa
- Source: Electronics Letters, Volume 16, Issue 25, p. 941 –942
- DOI: 10.1049/el:19800670
- Type: Article
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–942
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An optical system for easy introduction of phase-difference bias to optimise the sensitivity of the optical fibre laser gyro is proposed. The preliminary test set-up has been constructed and tested. A detectable limit of rotation of 8.7×10−4 rad/s has been achieved.
Low-threshold high-To constricted double heterojunction AlGaAs diode lasers
- Author(s): D. Botez and J.C. Connolly
- Source: Electronics Letters, Volume 16, Issue 25, p. 942 –944
- DOI: 10.1049/el:19800671
- Type: Article
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–944
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Constricted double heterojunction (c.d.h.) diode lasers of relatively low c.w. thresholds (28–40 mA) are obtained by growing structures that maximise the amount of current flow into the lasing spot. These values are obtained while still using standard 10 μm wide oxide-defined stripe contacts. Over the 20–70°C temperature interval, we find threshold current temperature coefficients as high as 320°C and a virtually constant external differential quantum efficiency.
New technique for channel synchronisation in time division multiplexing
- Author(s): K. Dagakis ; C. Mantakas ; G. Papadopoulos
- Source: Electronics Letters, Volume 16, Issue 25, p. 944 –945
- DOI: 10.1049/el:19800672
- Type: Article
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A channel synchronisation technique is described for t.d.m. systems carrying voice or teletype signals. According to this method, no extra sync signal is transmitted and synchronisation is extracted from the information signal. Furthermore, some encryption of the signal is achieved in this way. Tests had quite satisfactory results.
Reflection coefficient optimisation at feed of parabolic antenna fitted with vertex plate
- Author(s): H. Cory and Y. Leviatan
- Source: Electronics Letters, Volume 16, Issue 25, p. 945 –947
- DOI: 10.1049/el:19800673
- Type: Article
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An expression giving the reflection coefficient at the feed of a parabolic antenna fitted with a vertex plate is minimised. The parameters open to optimisation are the vertex plate radius and its distance from the centre of the antenna. Graphs of the reflection coefficient as a function of frequency for some optimisation frequencies are given and compared with the corresponding graphs obtained from another method and from the case where the vertex plate is missing.
Further results on relationship between system delay and transmission rate in time encoded speech-type systems
- Author(s): L.F. Turner ; E. Frangoulis ; A. Alcaim
- Source: Electronics Letters, Volume 16, Issue 25, p. 947 –948
- DOI: 10.1049/el:19800674
- Type: Article
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–948
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Explicit expressions are derived for the limiting delay in time encoded speech-type systems operating at data transmission rates higher than the average rate at which information is produced by the variable-rate source.
Diode laser sensor
- Author(s): A. Dandridge ; R.O. Miles ; T.G. Giallorenzi
- Source: Electronics Letters, Volume 16, Issue 25, p. 948 –949
- DOI: 10.1049/el:19800675
- Type: Article
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–949
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A new sensor capable of detecting sinusoidal displacements as small as ∼9 ×10−5 nm has been constructed. The sensor, employing phase modulation of light fed back into the laser cavity by an external reflector, has been successfully tested as an acoustic sensor.
Soft decision decoding with unknown source distribution
- Author(s): M. Wolfenson and V.C. da Rocha
- Source: Electronics Letters, Volume 16, Issue 25, p. 949 –950
- DOI: 10.1049/el:19800676
- Type: Article
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–950
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A soft decision approach is given for decoding the output of a noisy binary communication system with an unknown source probability distribution and a memoryless channel. The novelty of our procedure is the use of probabilistic conditional confidence coefficients as a measure of reliability, leading to a conditional maximum likelihood decoding rule.
All-pole filter with predistorted attenuation characteristic
- Author(s): D. Rabrenović and V. Jovanović
- Source: Electronics Letters, Volume 16, Issue 25, p. 950 –952
- DOI: 10.1049/el:19800677
- Type: Article
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–952
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A simple predistortion technique is presented to decrease the effect of losses in polynomial filters. The technique is based on a special class of filtering functions with monotonically decreasing passband attenuation response. With lossy elements this type of function provides a substantially flat passband attenuation characteristic.
Measurement of s.a.w. device stripe/period ratio using optical diffraction
- Author(s): C.W. Chapman and G.W. Judd
- Source: Electronics Letters, Volume 16, Issue 25, p. 952 –953
- DOI: 10.1049/el:19800678
- Type: Article
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–953
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The stripe/period ratio of periodic s.a.w. device masks has been determined by measuring the intensity of the diffraction maxima obtained when a laser beam is transmitted through the mask. Correlation of measured data with theoretical results is excellent. The technique can also be used to measure the stripe/period ratio on actual s.a.w. devices.
New direction-of-motion Doppler detector
- Author(s): M.J. Lazarus ; F.R. Pantoja ; M. Somekh ; S. Novak ; S. Margison
- Source: Electronics Letters, Volume 16, Issue 25, p. 953 –954
- DOI: 10.1049/el:19800679
- Type: Article
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–954
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A new phenomenon has been observed with self-oscillating mixers which permits discrimination between approaching and receding homodyne radar targets. The detected Doppler low frequency signal shows nonsinusoidal asymmetry which allows signal processing circuitry to give gated display outputs for positive or negative Doppler shift of the microwaves. The phenomenon has been observed with GaAs and InP Gunn devices, and with silicon Impatt devices, thus demonstrating its general nature. The effect has been shown with both c.w.1.2 and pulsed3 self-oscillating mixers, and confirmed at 15, 33, 66 and 75 GHz.
Comment: Polarisation characteristics in long length v.a.d. single-mode fibres
- Author(s): M. Monerie ; L. Jeunhomme ; C. Vassallo
- Source: Electronics Letters, Volume 16, Issue 25, p. 954 –955
- DOI: 10.1049/el:19800680
- Type: Article
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–955
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An assumption stated in a previous letter, concerning states of polarisation of a single-mode fibre, is criticised. Experimental proof is required to support the assumption.
Reply: Polarisation characteristics in long length v.a.d. single-mode fibres
- Author(s): K. Okamoto ; Y. Sasaki ; T. Miya ; M. Kawachi ; T. Edahiro
- Source: Electronics Letters, Volume 16, Issue 25, page: 955 –955
- DOI: 10.1049/el:19800681
- Type: Article
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Efficient laser-diode-single-mode-fibre coupling using two confocal lenses
- Author(s): M. Saruwatari and T. Sugie
- Source: Electronics Letters, Volume 16, Issue 25, p. 955 –956
- DOI: 10.1049/el:19800682
- Type: Article
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–956
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A new method for coupling a laser diode to a single-mode fibre is described. It uses a spherical ruby lens and a g.r.i.n. rod lens, which are positioned nearly under confocal conditions. A high coupling efficiency of more than −3 dB has been realised, and stringent alignment tolerances required for conventional coupling circuits have been overcome.
Novel p.s.k. tanlock loop
- Author(s): A.H. Makarious and P.G. Farrell
- Source: Electronics Letters, Volume 16, Issue 25, p. 957 –958
- DOI: 10.1049/el:19800683
- Type: Article
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p.
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–958
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A new loop for coherent demodulation of suppressed carrier phase-shift-keyed (p.s.k.) signals is presented. The p.s.k. tanlock loop (p.s.k.-t.l.l.) has a wider tracking range and faster phase acquisition than the Costas or squaring loops usually used for p.s.k. suppressed carrier tracking, but it has a greater tendency to false lock.
Current sensing with metal-coated multimode optical fibres
- Author(s): G.L. Tangonan ; D.I. Persechini ; R.J. Morrison ; J.A. Wysocki
- Source: Electronics Letters, Volume 16, Issue 25, p. 958 –959
- DOI: 10.1049/el:19800684
- Type: Article
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p.
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–959
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A multimode fibre has been used to detect electrical currents. The optical fibre which serves as the sensor is coated with a thick Al metal jacket. Electromotive forces on a wire in a magnetic field are used to induce differential phase shifts between the fibre modes. Good linearity has been observed in the 5 to 2000 mA current range.
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