Low-cost Transmitter Research Articles

High-Integration and Low-Cost Transmitter Packaging Solution for 0.2 THz SiP Application Using HTCC Technology

A high-integration and low-cost transmitter packaging solution for 0.2-THz system-in-package (SiP) application is newly presented using high-temperature co-fired ceramic (HTCC) technology. To improve 3-D integration, internal vertical air-filled interconnection waveguides buried in the HTCC package are explored and fabricated. A compact MoCu waveguide bandpass filter (BPF) is designed and integrated into the package to suppress the harmonic output of the mixer. To demonstrate the potential SiP application in the future 0.2-THz radar systems, based on the proposed solution, two 0.2-THz transmitters using frequency multipliers/mixer are designed, fabricated, and measured. All the components are buried in HTCC, and the overall size is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$36\times 14\times9.8$ </tex-math></inline-formula> mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$54\times 14.5\times9.8$ </tex-math></inline-formula> mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> , respectively. Both the transmitters show good performance, and the measured output power is better than 8 and 5 dBm, respectively.

Self-damping of the relaxation oscillations in miniature pulsed transmitter for sub-nanosecond-precision, long-distance LIDAR

Peak power is a critical factor for sub-nanosecond-pulsed transmitters utilizing laser diodes (LD) and applied to long distance LIDARs (light detection and ranging) for drones and automotive applications. Receiver speed is not anymore a limiting factor thanks to replacing linear (typically avalanche) detectors and a broad-band amplifier with a single photon avalanche detector (SPAD). Consequently the transmitters become the bottle neck in the resolution and ranging. The simplest and lowest-possible-cost transmitter consists of a switch, an LD, a storage capacitor C, and unavoidable parasitic loop inductance L. In the resulting resonant circuit, the principal problem consists of suppressing relaxation oscillations. Traditional way of oscillation damping reduce peak current and increase the pulse width. Here we show that specific transient properties of a Si avalanche switch solves the problem automatically provided the inductance is sufficiently low. This finding advances the state-of-the-art by reaching 90 W/1ns/200 kHz pulses from a miniature low-cost transmitter based on Si avalanching bipolar junction transistor (ABJT). Besides, the same self-damping effect may be realized in other switches maintaining significant residual voltage despite of fast current reduction.

High-Speed Measurement-Device-Independent Quantum Key Distribution with Integrated Silicon Photonics

Measurement-device-independent quantum key distribution (MDI-QKD) removes all detector side channels and enables secure QKD with an untrusted relay. It is suitable for building a star-type quantum access network, where the complicated and expensive measurement devices are placed in the central untrusted relay and each user requires only a low-cost transmitter, such as an integrated photonic chip. Here, we experimentally demonstrate a 1.25 GHz silicon photonic chip-based MDI-QKD system using polarization encoding. The photonic chip transmitters integrate the necessary encoding components for a standard QKD source. We implement random modulations of polarization states and decoy intensities, and demonstrate a finite-key secret rate of 31 bps over 36 dB channel loss (or 180 km standard fiber). This key rate is higher than state-of-the-art MDI-QKD experiments. The results show that silicon photonic chip-based MDI-QKD, benefiting from miniaturization, low-cost manufacture and compatibility with CMOS microelectronics, is a promising solution for future quantum secure networks.

High-Throughput Low-Power Area-Efficient Outphasing Modulator Based on Unrolled and Pipelined Radix-2 CORDIC

In this article, a high-throughput, high-accuracy, area-efficient, and energy-efficient digital outphasing modulator (OPM) is proposed for millimeter-wave transmitters. This digital OPM is entirely based on the fixed-point unrolled and pipelined radix-2 COordinate Rotation Digital Computer (CORDIC) algorithm, which is suitable for outphasing transmitters based on both IQ and phase modulation architectures. The outphasing angle is calculated by a mixture of single-CORDIC and double-CORDIC algorithm, which significantly reduces the critical path delay. Due to architectural advantages, its error performance, sampling rate, power efficiency, and area efficiency are improved. According to FPGA implementation measurements, this architecture enables a 12-bit OPM to achieve error vector magnitude (EVM) of 0.062% and peak sampling rate of 0.74 GSample/s. According to the postlayout spice-level simulation in 65-nm CMOS, a high-throughput version can work at a peak data rate of 1.85 GSample/s at 1-V supply. A low-power version reduces the area consumption to only 0.088 mm2, consuming 28.1 pJ/Sample at 0.78 GSample/s at 0.8-V supply. The proposed high-throughput OPM with the minimized area is expected to further open up an application area of energy-efficient low-cost millimeter-wave transmitters.

Monitoring Forest Phenology and Leaf Area Index with the Autonomous, Low-Cost Transmittance Sensor PASTiS-57

Land Surface Phenology (LSP) and Leaf Area Index (LAI) are important variables that describe the photosynthetically active phase and capacity of vegetation. Both are derived on the global scale from optical satellite sensors and require robust validation based on in situ sensors at high temporal resolution. This study assesses the PAI Autonomous System from Transmittance Sensors at 57° (PASTiS-57) instrument as a low-cost transmittance sensor for simultaneous monitoring of LSP and LAI in forest ecosystems. In a field experiment, spring leaf flush and autumn senescence in a Dutch beech forest were observed with PASTiS-57 and illumination independent, multi-temporal Terrestrial Laser Scanning (TLS) measurements in five plots. Both time series agreed to less than a day in Start Of Season (SOS) and End Of Season (EOS). LAI magnitude was strongly correlated with a Pearson correlation coefficient of 0.98. PASTiS-57 summer and winter LAI were on average 0.41 m2m−2 and 1.43 m2m−2 lower than TLS. This can be explained by previously reported overestimation of TLS. Additionally, PASTiS-57 was implemented in the Discrete Anisotropic Radiative Transfer (DART) Radiative Transfer Model (RTM) model for sensitivity analysis. This confirmed the robustness of the retrieval with respect to non-structural canopy properties and illumination conditions. Generally, PASTiS-57 fulfilled the CEOS LPV requirement of 20% accuracy in LAI for a wide range of biochemical and illumination conditions for turbid medium canopies. However, canopy non-randomness in discrete tree models led to strong biases. Overall, PASTiS-57 demonstrated the potential of autonomous devices for monitoring of phenology and LAI at daily temporal resolution as required for validation of satellite products that can be derived from ESA Copernicus’ optical missions, Sentinel-2 and -3.

112 Gbit/s transmitter optical subassembly based on hybrid integrated directly modulated lasers

Based on the hybrid integration technology, an ultra-compact and low cost transmitter optical subassembly module is proposed. Four directly modulated lasers are combined with a coarse wavelength division multiplexer operated at the O-band. The bandwidth for all channels is measured to be approximately 3 GHz. The 112 Gb/s transmission is experimentally demonstrated for a 10 km standard single mode fiber (SSMF), in which an optical isolator is used for avoiding the back-reflected and scattered light to improve the bit error rate (BER) performance. A low BER and clear eye opening are achieved for 10 km transmission.

TWDM-PON Burst Mode Lasers With Reduced Thermal Frequency Shift

For emerging TWDM-PON systems, based on burst-mode operation over WDM channels, a main challenge is the laser self-heating during bursts. This effect creates a drift of the emission frequency, leading to degraded transmission performances, and perturbation of adjacent channels. We explain an accurate method for characterization of wavelength drift during bursts at a bit time level, and use this method along the paper to characterize frequency drifts in burst-mode operation. First, we present an optimized directly modulated laser design for reduced self-heating, compatible for 100 GHz-spaced systems. Then, we propose a new solution based on counter-heating of the laser with a side heater, enabling to reduce self-heating induced frequency drift. This counter-heating scheme is applied to a standard laser, demonstrating a stringent reduction of frequency drift, and making it compatible for 100-GHz-spaced TWDM-PON transmissions. This simple method opens the way for simple low-cost transmitters in dense and high power TWDM-PON systems.

Visible-Light Multi-Gb/s Transmission Based on Resonant Cavity LED With Optical Energy Feed

Multi-Gb/s visible-light communication is demonstrated using a commercial off-the-shelf resonant-cavity light emitting diode (LED), which is originally rated for 150 Mb/s. By applying analog frequency response equalization and multi-carrier modulation schemes, a transmission capacity of up to 4.3 Gb/s is obtained over a single wavelength in a close-proximity scenario. Nyquist-shaped multi-band modulation and orthogonal-frequency-division multiplexing are applied with high spectral sub-carrier efficiencies of up to 8 b/symbol. The transmission rate is experimentally investigated as a function of the loss budget and further related to link reach based on free-space measurements under clear weather conditions. Analog signal transmission is also validated using real-time signal (de-)modulation with a high-definition video payload. We further demonstrate that on/off keying in combination with simpler baseband modulation can be facilitated for data rates of up to 750 Mb/s. This proves that commercially available LEDs can serve as a versatile low-cost transmitter. Finally, the joint transmission of energy and data has been validated. A power feed with an irradiance of 240 W/m2 is experimentally shown to enable a remotely supplied optical burst receiver for periodic access to Gb/s data rates.

Bidirectional optical subassembly-shaped 20 - Gbit / s compact single-mode four-channel wavelength-division multiplexing optical modules for optical multimedia interfaces

Low-cost single-mode four-channel optical transmitter and receiver modules using the wavelength-division multiplexing (WDM) method have been developed for long-reach fiber optic applications. The single-mode four-channel WDM optical transmitter and receiver modules consist of two dual-wavelength optical transmitter and receiver submodules, respectively. The integration of two channels in a glass-sealed transistor outline-can package is an effective way to reduce cost and size and to extend the number of channels. The clear eye diagrams with more than about 6 dB of the extinction ratio and the minimum receiver sensitivity of lower than −16 dBm at a bit error rate of 10−12 have been obtained for the transmitter and receiver modules, respectively, at 5 Gbps/channel. The 4K ultrahigh definition contents have been transmitted over a 1-km-long single-mode fiber using a pair of proposed four-channel transmitter optical subassembly and receiver optical subassembly.

Binary Continuous Phase Modulations Robust to a Modulation Index Mismatch

We consider binary continuous phase modulation (CPM) signals used in some recent low-cost and low-power consumption telecommunications standard. When these signals are generated through a low-cost transmitter, the real modulation index can end up being quite different from the nominal value employed at the receiver and a significant performance degradation is observed, unless proper techniques for the estimation and compensation are employed. For this reason, we design new binary schemes with a much higher robustness. They are based on the concatenation of a suitable precoder with binary input and a ternary CPM format. The result is a family of CPM formats whose phase state is constrained to follow a specific evolution. Two of these precoders are considered. We will discuss many aspects related to these schemes, such as the power spectral density, the spectral efficiency, simplified detection, the minimum distance, and the uncoded performance. The adopted precoders do not change the recursive nature of CPM schemes. So these schemes are still suited for serial concatenation, through a pseudo-random interleaver, with an outer channel encoder.

Robust Detection of Binary CPMs With Unknown Modulation Index

We consider soft-output detection of a binary continuous phase modulation (CPM) generated through a low-cost transmitter, thus characterized by a significant modulation index uncertainty, and sent over a channel affected by phase noise. The proposed detector is designed by adopting a simplified representation of a binary CPM signal with the principal component of its Laurent decomposition and is obtained by using the framework based on factor graphs and the sum-product algorithm. It does not require an explicit estimation of the modulation index nor of the channel phase and is very robust to large uncertainties of the nominal value of the modulation index. Being soft-output in nature, this detector can be employed for iterative detection/decoding of practical coded schemes based on a serial concatenation, possibly through a pseudo-random interleaver, of an outer encoder and a CPM modulation format.

160-GHz to 1-THz Multi-Color Active Imaging With a Lens-Coupled SiGe HBT Chip-Set

This paper presents the concept and implementation of an active all-electronic terahertz multi-color imager with the functionality demonstrated in the frequency range of 160 GHz–1 THz. The proposed terahertz system is realized in the form of two independent highly integrated low-cost transmitter (Tx) and receiver (Rx) modules. Each module consists of a single silicon die with a silicon lens-coupled ultra-wideband on-chip antenna and is assembled onto a low-cost FR-4 printed circuit board using traditional wire-bonding. The chip-set is implemented in a ${\hbox{0.25}}~\mu{\hbox {m}}$ SiGe HBT BiCMOS process with $f_{T}/f_{\max}$ of 280/435 GHz. The main Tx path is composed of an antenna-coupled harmonic generator and is driven by a $\times $ 9 multiplier chain fed from an external reference signal centered around 17–18 GHz. Four identical Tx paths are spatially combined on a single chip to increase the output power. The Rx chip shows a 2 $\times$ 2 arrangement of identical antenna-coupled broadband sub-harmonic mixers driven by a single $\times $ 9 multiplier chain; similar to that from the Tx circuit. The system operates simultaneously at six harmonics being multiple numbers of 165 GHz. The signal-to-noise ratio in transmission-mode active imaging with a 1-Hz resolution bandwidth is 90 dB for 165-GHz band, 115 dB for 330- and 495-GHz bands, 95 dB for 660- and 820-GHz bands, and 70 dB for 990-GHz band.

WDM–TDM NG-PON Power Budget Extension by Utilizing SOA in the Remote Node

Today, even in access networks, data traffic is enormously increasing, a trend that causes existing passive optical network (PON) infrastructures to become bottlenecks in a tele- and data-communication infrastructure, which is aimed to be both broadband and seamless. Thus, two major objectives are considered for next-generation PONs (NG-PONs), i.e., first, bandwidth increase, and second, reach extension to reduce deployment costs. Here, we describe a new reach extension scheme that at the same time allows increasing the number of subscribers in the network. The amplification technique is based on a bidirectional semiconductor optical amplifier (SOA). It is shown that the extender configuration not only meets the bandwidth and budget requirements for NG-PONs but also remarkably improves them. Differential (quadrature) phase-shift keying (D(Q)PSK) signals are investigated in this paper. Hybrid wavelength-division multiplexing/time-division multiplexing (WDM/TDM) transmission up to 120-Gb/s downstream and 40-Gb/s upstream are experimentally demonstrated. The access budget of 33.4 dB is achieved at 10 Gb/s on every WDM channel in case of DPSK enabling a splitting ratio of 1:512 per wavelength. Furthermore, optical power budget of 40 dB is obtained when DQPSK is used, where a splitting ratio of 1024 per wavelength can be supported. Additionally, a cost-efficient chirped managed directly modulated laser scheme is proposed for DPSK signal generation in U.S. scenario enabling a high-power budget performance low-cost transmitter configuration, which appears suitable for NG-PON application. The proposed technique also alleviates nonlinear impairments [specifically, cross-phase modulation (XPM)], which appear in dense WDM transmission.

Building better microbatteries: from fundamental research to manufacturing

The Endangered Species Act requires actions that improve the passage and survival rates for migrating salmonoids and other fish species that sustain injury and mortality when passing through hydroelectric dams. To develop a low-cost revolutionary acoustic transmitter that may be injected instead of surgically implanted into the fish, one major challenge that needs to be addressed is the micro-battery power source. This work focuses on the design and fabrication of micro-batteries for injectable fish tags. High pulse current and required service life have both been achieved as well as doubling the gravimetric energy density of the battery. The newly designed micro-batteries have intrinsically low impedance, leading to significantly improved electrochemical performances at low temperatures as compared with commercial SR416 batteries. Successful field trial by using the micro-battery powered transmitters injected into fish has been demonstrated, providing an exemplary model of transferring fundamental research into practical devices with controlled qualities.

High Way Vehicle Speed Control &amp; Automatic Breaking System

Every year, we find more and more road accidents due to increased traffic on the roads, and if you see the statistics, you will find that the causalities are more every year than that of 1970 Indo -Pak war. Experts say, increased motorist population, long working hours and stressful life are the major reasons for the rise in road accidents. The factors are beyond one's control, but if we could alert the driver on the highway, could save many precious lives. We haven't presented a very complex solution for this; neither claimed to be expert traffic controllers. Usually fixing some sort of transmitter system on the highways which can detect the speed of the vehicle and convey to the driver that he is not in the permitted speed limit in a particular area is quite common and expensive. As a simple solution, we have pre installed low cost transmitters on required locations to convey the speed limit information, even further, if the automatic breaking system could be actuated on over speed is a decent approach. We have designed and developed a prototype system of a transmitter and receiver modules. Receiver(s) is (are) kept in the vehicle(s) and transmitter(s) are set up on the road side. As it is a prototype, we have not used any speed sensing devices, instead four switches are used as alternative. The four switches represents or assumes various speed limits say limit 80 switch, limit40 switch, limit20 switch and no horn area. Whenever these switches are pressed, they will transmit the corresponding alert message to the driver so that the driver can handle the situation sensibly. Receiver section has a 2x16 LCD, which will display the alert message, and there exists microcontroller to receive the data and activate the relay circuitry to give a buzzer and to control the speed of the dc motor which acts as a prototype for automatic braking and vehicle speed reduction mechanism.

Experimental evaluation and improvement methods for low cost transmitters in long reach PONs

An extensive experimental research of an optical access network behaviour has been realized, in the framework of studying distance enhancement of long reach passive optical networks (PONs), while maintaining low cost and high performance. The network system has been implemented with low cost transmitters – operated at low driving voltage, without the use of electrical amplification, at 10Gb/s – and with colourless optical network units (ONUs) as receivers. Although studied for variable lengths, error-free transmission (target bit-error rate at 10−9) over 100km reach has been achieved in several ways. The performance of extended PONs, when low cost transmitters operated at low driving voltage are utilized, is improved by the application of optical dispersion compensation and electronic equalization techniques. The chirp of the transmitter has been shown to have an important effect on the behaviour of the system because of the dispersion phenomenon. It is observed however, that the combined use of optical dispersion compensation and electronic equalization gives a reduction of 5–10dB of the required optical signal to noise ratio (OSNR) for an error-free transmission. Moreover, it significantly reduces the heterogeneity of the system performance for several distances, yielding a predictable behaviour, while at the same time permits the use of handy, inexpensive and integrated transmitters.

Radio Frequency Tomography for Tunnel Detection

Radio frequency (RF) tomography is proposed to detect underground voids, such as tunnels or caches, over relatively wide areas of regard. The RF tomography approach requires a set of low-cost transmitters and receivers arbitrarily deployed on the surface of the ground or slightly buried. Using the principles of inverse scattering and diffraction tomography, a simplified theory for below-ground imaging is developed. In this paper, the principles and motivations in support of RF tomography are introduced. Furthermore, several inversion schemes based on arbitrarily deployed sensors are devised. Then, limitations to performance and system considerations are discussed. Finally, the effectiveness of RF tomography is demonstrated by presenting images reconstructed via the processing of synthetic data.

Approximation Algorithms for Minimum Energy Transmission Scheduling in Rate and Duty-Cycle Constrained Wireless Networks

We consider a constrained energy optimization called minimum energy scheduling problem (MESP) for a wireless network of <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> users transmitting over <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</i> time slots, where the constraints arise because of interference between wireless nodes that limits their transmission rates along with load and duty-cycle (on-off) restrictions. Since traditional optimization methods using Lagrange multipliers do not work well and are computationally expensive given the nonconvex constraints, we consider approximation schemes for finding the optimal (minimum energy) transmission schedule by discretizing power levels over the interference channel. First, we show the toughness of approximating MESP for an arbitrary number of users <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> even with a fixed <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</i> . For any <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</i> > 0, we demonstrate that there does not exist any ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</i> , <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</i> )-bicriteria approximation for this MESP, unless <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P</i> = <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">NP</i> . Conversely, we show that there exist good approximations for MESP with given <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> users transmitting over an arbitrary number of <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</i> time slots by developing fully polynomial (1,1+¿) approximation schemes (FPAS). For any ¿ > 0, we develop an algorithm for computing the optimal number of discrete power levels per time slot ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">O</i> (1/¿)), and use this to design a (1, 1+¿)-FPAS that consumes no more energy than the optimal while violating each rate constraint by at most a 1+¿-factor. For wireless networks with low-cost transmitters, where nodes are restricted to transmitting at a fixed power over active time slots, we develop a two-factor approximation for finding the optimal fixed transmission power value <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">opt</sub> that results in the minimum energy schedule.

Integrated sub-harmonically pumped up-converter antenna for spatial power combining

A Ka-band sub-harmonically pumped up-converter antenna employing the substrate integrated waveguide (SIW) technique is proposed and used to realise a low-cost transmitter together with spatial power combining architecture in this paper. A single Ka-band sub-harmonically pumped up-converter using SIW band-pass filter is developed, exhibiting a conversion loss of about 7 dB. Based on the designed up-converter and SIW feeding antipodal linearly tapered slot antenna (SIW-ALTSA), the integrated up-converter antenna is designed and fabricated. Measured results of equivalent isotropic radiated power (EIRP) and radiation patterns are given. Finally, a 2 2 up-converter antenna array is designed and fabricated. Measured result shows the array has a power combining efficiency of above 90 and IM3 EIRP of 16 dBm. In close-range point-to-point communication and radar systems, the demonstrated millimetre-wave sub-harmonically pumped up-converter antenna array can be considered as a transmitter because of its low cost, high dynamic range and high linearity.

A Precision, Low-Cost GPS-Based Transmitter Synchronization Scheme for Improved AM Reception

This paper describes a highly accurate carrier-frequency synchronization scheme for actively, automatically locking multiple, remotely located AM broadcast transmitters to a common frequency/timing reference source such as GPS. The extremely tight frequency lock (to ~1 part in 109 or better) permits the effective elimination of audible and even sub-audible beats between the local (desired) station's carrier signal and the distant stations' carriers, usually received via skywave propagation during the evening and nighttime hours. These carrier-beat components cause annoying modulations of the desired station's audio at the receiver and concurrent distortion of the audio modulation from the distant station(s) and often cause listeners to ldquotune outrdquo due to the low reception quality. Significant reduction or elimination of the beats and related effects will greatly enlarge the effective (interference-limited) listening area of the desired station (from 4 to 10 times as indicated in our tests) and simultaneously reduce the corresponding interference of the local transmitter to the distant stations as well. In addition, AM stereo (CQUAM) reception will be particularly improved by minimizing the phase shifts induced by co-channel interfering signals; hybrid digital (HD) signals will also benefit via reduction in beats from analog signals. The automatic frequency-control hardware described is inexpensive ($1000-$2000), requires no periodic recalibration, has essentially zero long-term drift, and could employ alternate wide-area frequency references of suitable accuracy, including broadcasts from WWVB, LORAN-C, and equivalent sources. The basic configuration of the GPS-disciplined oscillator which solves this problem is extremely simple. The main oscillator is a conventional high-stability quartz-crystal type. To counter long- term drifts, the oscillator is slightly adjusted to track a high-precision source of standard frequency obtained from a specialized GPS receiver (or other source), usually at 10.000 MHz. This very stable local reference frequency is then used as a clock for a standard digitally implemented frequency synthesizer, which is programmed to generate the specific carrier frequency desired. The stability of the disciplining source, typically ~1 part in 109 to 1011, is thus transferred to the final AM transmitter carrier output frequency.