In a recent Forum post here on dsprelated.com the audio signal processing subject of stereophonic amplitude-panning was discussed. And in that Forum thread the so-called "Tangent Law", the fundamental principle of stereophonic amplitude-panning, was discussed. However, none of the Forum thread participants had ever seen a derivation of the Tangent Law. This blog presents such a derivation and...
To enable interoperability amongst RF systems, the military and industry rely on standardized dimensions and types of coaxial connectors. The two major standards that define coaxial connectors for the US military are MIL-STD-348 and MIL-PRF-39012. MIL-STD-348 provides the dimensions for control of the standard interfaces, while MIL-PRF-39012 defines the, detail specifications, materials, quality conformance, qualification, and verification for coaxial connectors. As a greater number of industries and applications adopt Hi-Rel coaxial cable assemblies, both MIL-PRF-39012 and MIL-STD-348 are becoming increasingly valuable in manufacturing and sourcing coaxial cable connectors and adapters. Hi-Rel coaxial connectors are used with virtually all RF devices and assemblies that require RF transmission line interconnect, other than waveguide. This includes common assemblies, such as amplifiers, transceivers, filters, antennas, mixers, attenuators, combiners/splitters, couplers, and many other devices and components.
MIL-PRF-39012 can be compared to MIL-DTL-17 for coaxial cables, as they both involve visual, mechanical, and electrical testing in several stages to uphold quality standards. This standard also requires that manufacturing facilities and processes meet quality standards and that the parts covered by the specification can be listed on the Qualified Products List (QPL). Coaxial connectors and adapters that meet MIL-PRF-39012 are well suited to military, and non-military use for a wide range of Hi-Rel applications, including radar, RF instrumentation and test equipment, transceivers, ruggedized RF/microwave assemblies, SATCOM ground equipment, indoor/outdoor antennas, transportation, and aerospace RF/microwave assemblies.
Materials used for MIL-PRF-39012 qualified connectors are specified in referenced industrial standards, listed in the following table.MIL-PRF-39012F Materials Material Applicable Specifications Steel ASTM A484/A484M, ASTM A582/A582M Brass ASTM B16/B16M, ASTM B36/B36M, ASTM B121/B121M, ASTM B455 Phosphor bronze ASTM B139/B139M Soft copper ASTM B152/B152M Copper ASTM B88, ASTM B124/B124M Copper-Beryllium ASTM B194, ASTM B196/B196M, ASTM B197/B197M PTFE fluorocarbon ASTM D4894, ASTM D4895 FEP fluorocarbon ASTM D2116 Silicon rubber A-A-59588
A key aspect of MIL-PRF-39012 connectors is that the center pin for qualified connectors must be gold-plated to a standardized depth, adhesion quality, and finish. The gold plating on the captivated contacts ensures a minimized insertion loss and consistent electrical contact over time and exposure to the environment.
The types of connectors specified in MIL-PRF-39012 include the following:
MIL-DTL-348 specifies the United States standard interfaces for RF coaxial connectors, which are universally accepted by all US military services. Hence, these connectors are very commonly used in, and outside of military applications, even if the application doesn’t specifically require the use of this standard. The benefit is that MIL-DTL-348 brings interoperability of coaxial connectors, as well as a basis for Hi-Rel design and construction of these components.
MIL-STD-348 includes the RF connectors and adapters referenced in other MIL-SPEC documents:
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MIL-DTL-17, formerly known as MIL-C-17, is the US military specification (MIL-SPEC) that defines the standards and procedures for qualifying and verifying flexible and semi-rigid coaxial cable for Hi-Rel applications. Because of the rigorous requirements of MIL-DTL-17, many applications that require high reliability (Hi-Rel) coaxial cable may opt for, or require, MIL-DTL-17 coax. There are many requirements and aspects of MIl-DTL-17 coaxial cable, including the following:
• Design and construction
• Visual and mechanical
Hence, a coaxial cable won’t fulfill the MIL-DTL-17 specification unless it meets each category of criteria. Depending on the application, some “Hi-Rel” coaxial cables may call out only specific requirements of the MIL-DTL-17 specification. There are four key areas of inspections detailed in the specification, material, qualification, conformance, and final inspection. Failure at any of these inspections often requires discarding failed parts and/or re-inspection.
As part of these inspections, there are several electrical and mechanical tests that must be performed. Some of these tests are only performed on qualifying batches of coaxial cable, while some tests are performed on each batch of coax to ensure conformance. These tests include:
• Dimensional measurements
• Dielectric withstand voltage
• Shield construction
• Characteristic impedance
• Conductor adhesion
Moreover, there are destructive tests performed on sample parts during conformance testing. These tests include:
• Capacitance stability
• Aging stability
• Stress crack resistance
• Outer conductor integrity
• Dimensional stability
• Heat distortion
• Tensile strength and elongation
• Physicals (aged)
Lastly, each coaxial cable is subject to a final inspection, which differs in requirements between semi-rigid cable and flexible cable:
• Semirigid Cable
> Voltage withstanding
• All other Cables
> Spark test
> Voltage withstanding
> Insulation resistance
> Out-of-roundness of jacket measurements
The exact parameters and methods of these tests are detailed in MIL-DTL-17, and/or are further detailed in referenced military and industrial specifications. These tests must also be performed in a qualified facility and the cables tested for qualification and conformance must be produced in the same was as production cables.
Many of the specifications within MIL-DTL-17 are referred to as “RG”, though RG coaxial cables have become a generalized industry term, and not a standardized set of cable specifications. For example, MIL-DTL-17 thoroughly describes maximum attenuation over a range of frequencies, along with precise physical properties, such as conductor plating thickness, and there are no such specifications defining RG coaxial cables. Moreover, a MIL-DTL-17 coaxial cable supplier should have their product on the Qualified Products List (QPL), which isn’t case for readily available RG coax.Resources
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Standardization and quality control surrounding solder and soldering practices for military electronics has been around for decades. Initially, the United States military used MIL-STD-454, MIL-S-45743, DOD-STD-2000, and MIL-STD-2000 to define soldering practices before merging with industry standards, such as IPC J-STD-001 and IPC J-STD-006. These standards attempt to ensure that the end results of a soldering operation produce a reliable connection that can be inspected and ensured to meet minimum standards of performance. This concept is essential for critical use cases like coaxial cable assemblies for Hi-Rel applications, and is part of creating MIL-DTL-17 assemblies .
If improper solders or soldering practices are used, instead of forming a mechanically and electrically strong bond, a bond may form with a variety of contaminates, undesirable intermetallic compounds, and other defects. These defects can compromise the integrity of the solder joint, reduce the reliable lifetime, increase insertion loss, and lead to hard-to-diagnose failures. Many of the defects that are caused by improper solder and soldering practices may not be visible to the eye initially, and may require trained technicians familiar with the standards and soldering to deduce the problem. Hence, the requirements for Hi-Rel coaxial cable assemblies often require further inspection and testing that ensures mechanical and electrical performance.
IPC J-STD-001 [2 ,3]
J-STD-001 is an industry standard guideline with details of practices and requirements for the manufacture of soldered connection for electrical and electronic assemblies. The practices and requirements laid out in J-STD-001 are divided into three classes based on the nature of their final use.
• CLASS 1 General Electronic Products
Includes products suitable for applications where the major requirement is function of the completed assembly.
•CLASS 2 Dedicated Service Electronic Products
Includes products where continued performance and extended life is required, and for which uninterrupted service is desired but not critical. Typically the end-use environment would not cause failures.
•CLASS 3 High Performance Electronic Products
Includes products where continued high performance or performance-on-demand is critical, equipment downtime cannot be tolerated, end-use environment may be uncommonly harsh, and the equipment must function when required, such as life support or other critical systems.
In the case of Hi-Rel coaxial cable assemblies, these coax assemblies are usually considered Class 3, which faces the most stringent requirements involving inspections and testing. Two other documents, IPC-HDBK-001 and PIC-A-610, are often considered companions to J-STD-001 and help to elaborate and clarify certain aspects of the standard. Within the standard, there are descriptions of soldering practices for a variety of electronics and assemblies, though only the general sections and sections on wire and cable apply to coaxial cable assemblies. The relevant sections describe preparation, suitable environments, process, and specific cases associated with wires and cables, such as allowable strand damage, insulation damage considerations, tinning wire, and etc.
IPC J-STD-006 [2,4]
J-STD-006 defines the requirements for solder (alloys) for electronic applications. Though not related to performance, J-STD-006 is intended to help ensure solder alloy quality, and further describes the methods of inspection and testing to that end. Where J-STD-006 discusses solder alloys, J-STD-004 covers soldering fluxes, and J-STD-005 discusses soldering pastes. Using J-STD-006 solder alloys and following associated industry standard practices for handling and use (J-STD-001), can aid in producing a reliable product that also provides quality assurance to customers.References
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The Internet of Things (IoT) is a predicted eventually when a vast number of everyday objects are augmented with internet connectivity and accessory capabilities. They keystone to these IoT device features is the ability for sensors, controllers, actuators, and displays to communicate through the common platform of the internet. As hardline internet, such as through Ethernet or fiber optic, isn’t viable for many applications and environments, a more flexible alternative is to use wireless communication methods between an IoT device and a wireless hub.
The ability to operate without a physical wired internet tether is extremely desirable for many applications. Some examples included patient monitoring for medical applications, wireless beacons in metropolitan store fronts or retail spaces, and with industrial applications interfacing between a large number of coordinating machines. As the diversity of wireless IoT devices is extensive, so are the wireless standards/protocols and methods of wireless communications used with these emerging devices. This blog will provide a brief overview of wireless standards commonly used, or considered, for IoT applications.
Wireless Standards Used In IoT Applications
Low-Power Wide Area (LPWA) Networks
• Long-Range (LoRa)
Medium/Short Range IoT Wireless Network Technology
• Zigbee/IEEE 802.15.4
• 4G LTE
• 5G Sub-6 GHz
• 5G Millimeter-wave *future applications
The majority of today’s common wireless standards used with IoT applications are at 2.4 GHz, where the ISM band that facilitates Bluetooth, Zigbee, Thread, WiFi, and other standards. Virtually all wireless IoT applications use frequencies below 6 GHz, some of the highest operating frequencies for IoT being 5 GHz WiFi and high-band cellular. However, future development of IEEE 802.11ah, 802.11af, or other TV White Space (TVWS) frequencies may allow for wireless IoT applications in non-cellular bands between 400 MHz and over 700 MHz (United States). The low frequencies of TVWS open up doors for low-power and still comparatively long range communication.
There are many considerations for choosing a particular standard over another. Each standard differs somewhat in the infrastructure, design resources, vendors, module size, difficulty of certification, and licensing cost. Moreover, the various wireless standards also operate on a wide range of frequencies, use different and sometimes unique modulation methods and protocols, have a wide range of maximum output power restrictions, power efficiencies, effective ranges, networking types, interference concerns, and complexity of design/installation.
Also, each country or region regulates radio frequencies in unlike ways, though there are some common wireless standards shared between some countries and regions. Hence, some wireless IoT devices operate in unlicensed bands, where others are licensed and require additional costs to operate in those bands and may be further restricted in location and operation by licensing agreements. Some wireless standards/protocols themselves are proprietary, and the hardware for the devices must be purchased from a licensed distributor, or IP licensing may be required. There are also wireless standards used for IoT that are open standards, such as LoRa and Thread, and are developed as an effort by many industry partners, experts, and associations.
After a wireless standard is selected an IoT OEM then needs to select devices that are certified in that standard, or build their own compliant devices. These devices are often communication chips, or microcontrollers/microprocessors (MCUs/MPUs) with integrated communication features. To implement a wireless standard, an OEM then needs to design such a device into a circuit along with the associated RF components, antenna, and interconnect that are compliant with the standard. Additional certification and compliance is often necessary to meet countries emission and susceptibility of electromagnetic interference (EMI), known as electromagnetic compliance (EMC).
Specifications of Common Wireless Standards Used in IoT Applications
In last week’s post we defined and explored the different types of tunable resonators that are available. This week we take a look at more resonator types and discuss the pros and cons of each.
Quartz crystals are used as high-quality electromechanical resonators due to their piezoelectric properties, that is, their ability to generate an electric charge in response to a mechanical stress. When a piezoelectric material is placed under mechanical stress, the positive and negative charge centers shift resulting in an external electrical field and, when reversed, an outer electrical field either stretches or compresses the piezoelectric material. In a quartz crystal resonator, this process begins with a thin slice of quartz cut to specific dimensions and is then placed between two electrodes. The cut determines the resonator physical and electrical parameters and is classified by the cut from the original crystal. For example, the AT crystal cut is used for electronic instruments where oscillators are required to run in the range 500 kHz to around 300 MHz. The BT cut is another example, similar to the AT cut, that provides repeatable characteristics with a frequency constant 2.536 MHz/mm. While the temperature stability characteristics are not as good as the AT cut, it can be used for higher frequency operation due to its higher frequency constant.
Although less accurate than quartz crystals, ceramic resonators are an alternative to the more costly crystal resonators. Like crystal resonators, ceramic resonators use the piezoelectric properties in the material, such as lead zirconium titanate (PZT). In this design, metal electrodes placed on the top and bottom of the ceramic substrate, a voltage is applied, and the substrate vibrates between the electrodes are energized, thus yielding a resonant frequency determined by the thickness of the material.
SAW and BAW Resonators
Much like crystal resonators, surface acoustic wave (SAW) resonators are components in oscillators found in higher-frequency applications. A SAW is made of an interdigital transducer with two grating reflectors that are placed on a piezoelectric material by a photolithographic process. This photolithographic process uses light to transfer a geometric pattern from a light-sensitive chemical photoresist, or resist, onto the substrate. The reflectors then form a resonant cavity that is coupled to the external circuit by the transducer. Applications include automotive remote-keyless-entry (RKE) devices, security systems, and garage door openers. Similarly, BAW resonators leverage bulk acoustic waves instead of surface acoustic waves to generate a resonant effect.
Yttrium iron garnet (YIG) resonators are used as components in the design of oscillators and filters. A YIG is a synthetic form of garnet with magnetic properties that exhibits a very high Q and low phase noise oscillations capable of achieving multi-octave bandwidths. In the sphere configuration, a single crystal of synthetic yttrium iron garnet acts as a resonator with the garnet mounted on a ceramic rod with a pair of small loops around the sphere couple fields where the loops are half-turns and positioned at right-angles to prevent direct EM coupling. One advantage of the YIG is that the garnet can be tuned over a wide frequency range by varying the strength of the magnetic field, anywhere from 3 GHz up to 50 GHz. YIG filters are usually made of several coupled stages where each stage is designed with a sphere and a pair of loops.
The post What are Tunable Resonators, and What do They Have to do With Filters and Oscillators? Part 2 appeared first on Pasternack Blog.
This blog briefly describes a remarkable integration algorithm, called "Romberg integration." The algorithm is used in the field of numerical analysis but it's not so well-known in the world of DSP.To show the power of Romberg integration, and to convince you to continue reading, consider the notion of estimating the area under the continuous x(t) = sin(t) curve based on the five...
Below is a little microprocessor history. Perhaps some of the ol' timers here will recognize a few of these integrated circuits. I have a special place in my heart for the Intel 8080 chip.
Image copied, without permission, from the now defunct Creative Computing magazine, Vol. 11, No. 6, June 1985.
A tunable resonator is a device used either to generate RF frequencies or select specific frequencies from a signal. It exhibits resonance in that it naturally oscillates at frequencies known as resonant frequencies. These oscillations can be either electromagnetic or mechanical. Tunable resonators are used in a wide range of radio devices, specifically tunable radios, test equipment, and frequency agile radar.
Types of Resonators
Resonators are key to the performance of oscillators and filters. The types of common resonators include transmission line and coaxial resonators, dielectric, crystal, ceramic, surface acoustic wave (SAW), bulk acoustic wave (BAW), and yttrium iron garnet (YIG).
Inductor/Capacitor (LC) Tank Circuit Resonator Example
Using a simple crystal radio as an example, the inductor/capacitor (LC) oscillator acts as the tuner for the radio. When radio signals are received that match the resonant frequency of the LC resonator circuit, they pass through with relatively low resistance. However, frequencies outside of the resonant frequency of the LC circuit are heavily attenuated. In this example, either the capacitor or the inductor in the resonator is adjustable so that when the tuner knob on the radio is turned, a variable element is adjusted which changes the resonant frequency of the resonator. Most RF and microwave filters are made up of one or more coupled resonators; the quality factor, or Q factor, of the resonator will determine the selectivity the filter can achieve.
Transmission Line Resonators and Coaxial Resonators
Transmission lines are structures that allow broadband transmission of electromagnetic waves at radio or microwave frequencies. Due to the nature of transmission lines, a section of transmission line can be selected to resonate at a particular frequency, and in essence, function as a tuned LC circuit with a very high Q factor. Planar transmission line resonators are used in coplanar, stripline, and microstrip transmission lines, can be compact in size, and are used in microwave circuitry. Coaxial resonators are used in voltage-controlled oscillators (VCOs), coaxial-resonator oscillators (CROs), and filter components. These resonators are used as components in oscillators, bandpass/bandstop filters, and electromagnetic-interference (EMI) filtering.
A dielectric resonator is a piece of nonconductive material, usually ceramic, designed to function as a resonator in the microwave and millimeter wave bands. The EM waves are confined inside the resonator by the rapid change in permittivity at the surface and bounce back and forth between the sides. At the resonant frequencies, the EM energy forms standing waves in the resonator, oscillating with large amplitudes. This resonant frequency is determined by the physical dimensions of the resonator and the dielectric constant of the material. Dielectric resonators can replace resonant cavities in components, such as filters and oscillators, and have a high εr value that provides an advantage in compact design. This type of resonator confines the EM fields which allows for only a small amount of loss while providing a high Q factor to be achieved. The main use for this type of resonator is in millimeter-wave electronic oscillators to control the frequency of the radio waves or as bandpass filters and antennas.
The post What are Tunable Resonators, and What do They Have to do With Filters and Oscillators? Part 1 appeared first on Pasternack Blog.