Editor's Picks

When Do You Need a Bias Tee or DC Block?

Pasternack Blog -

Bias Tees and DC blocks are both low frequency filters designed to pass certain wanted signals and power rails while blocking other signals and limiting the performance impact on RF/microwave circuits. Bias Tees are essentially diplexers with an extremely low crossover frequency, and DC blocks are high pass filters with cutoff frequency down to audio frequencies and DC.

DC blocks are used for enhancing signal-to-noise ratio and dynamic range on some very low frequency or wideband systems, as well as block DC and audio frequencies from testing that may require isolation from such low frequency components. DC blocks are also used for signal source modulation leakage suppression, and ground loop elimination.

Bias Tees are used to allow for DC currents and/or voltages to pass to RF devices while blocking RF/microwave signals on the same line. For example, a Bias Tee may be used to enable a power supply to a transistor or amplifier circuit, which requires a DC signal and would be disturbed by the RF content on the signal and power line. There are also pulsed bias tees, which allow for minimum distortion on current, or voltage, pulses for amplifiers and devices which require intermittent signals for biasing or power.

Bias Tees and DC blocks are both very commonly used in many RF/microwave circuits which require the conveyance of DC signals along the same coaxial or microstrip signal path as RF/microwave signals. Bias tees and DC blocks may even be used together at a node where the DC power or bias voltage/current is needed, but would be disruptive if it passed further down the RF transmission line.

Bias tees are used anywhere from cell phone amplifiers to test and measurement equipment. An example of this is with powered probes which have a power hookup at the same port as the RF signal port.

DC blocks are typically only used where powered RF transmission lines, or “hot” conductors, are used. However, DC blocks may also be used to separate a circuit from a ground place and DC and audio signals, to prevent current passing or voltage developing from that circuit node to ground. An example of this is in the instance where a voltage is injected into the source of a shunt FET, which is also grounded to the grounded housing or fixture of the assembly.

The post When Do You Need a Bias Tee or DC Block? appeared first on Pasternack Blog.

Tips on Selecting a Frequency Divider or Frequency Multiplier

Pasternack Blog -

Frequency translation is the backbone of superheterodyne communications and radar circuits, as well as many other useful RF/microwave devices. There is often confusion surrounding these nonlinear devices, specifically the role of mixers, multipliers, and dividers, and how to select the best device for an application. This post aims to briefly describe the similarities and differences, and some illumination on device selection criteria.

What is a Mixer?

A mixer is a nonlinear, three-terminal device, often comprised of a diode or transistor operating in the nonlinear region. From two input signals, a mixer will produce the sum and difference of the two signals in the output. This can be used in upconversion, downconversion, as an IQ mixer, or with different performance parameters based on configuration. Mixers are commonly used in demodulation circuitry, upconverters, and downconverters, providing frequency translation before transmission, or after reception.

What is a Multiplier?

A multiplier is a nonlinear device, which generates harmonics of higher frequencies based on an input signal’s behavior. For example, a doubler is a frequency multiplier that creates a strong 2nd harmonic. Inevitably, the input signal, higher harmonics, and noise/interference will also leak and be mixed in with the output signal. Multipliers are often used in demodulation circuitry and to raise the frequency of an oscillator or signal generator source.

What is a Divider?

A frequency divider is similar to a frequency multiplier, with the exception that the output frequencies are a submultiple of the input signal frequencies. The same considerations apply to dividers, as they do to multipliers.

What should I know when choosing Multipliers or Dividers?

As part of the many use cases of multipliers and dividers, isolation, harmonic suppression, and phase noise characteristics are important factors to consider when selecting a multiplier or divider. Isolation describes how well the signals input into the multiplier or divider are prevented from leaking into the output, while harmonic suppression describes how well the multiplier or divider design prevents harmonics of the input signal from appearing at the output. Both factors are critical, as they directly impact the usability of a multiplier or divider device. Additive phase noise and noise performance of a multiplier or divider are important for signal generation and modulation circuitry that is noise, phase noise, or interference limited, as these parameters describe with the device adds to an input signal when generating the output signal.

The amount of signal power needed to drive the multiplier or divider, or necessary signal input power for proper operation, may also be a factor to consider, as some multipliers and dividers require substantial input powers. Many test and measurement grade precision signal generators, and arbitrary waveform generators, may not produce the necessary signal strength to drive a multiplier or divider. Hence, an amplifier, which as its own distortion, noise, and phase noise, may be required.

The post Tips on Selecting a Frequency Divider or Frequency Multiplier appeared first on Pasternack Blog.

Directional Coupler Do’s and Don’ts

Pasternack Blog -

Directional couplers are extremely useful passive RF components capable of extracting a small portion of the energy from the main transmission path, and redirecting it to one, or more, coupled ports. As isolation from the coupled ports to the main transmission path is desirable, directional couplers typically have high isolation among the ports. There are two main types of directional couplers, a standard directional coupler with a single coupled port and a terminated port, and a bi-directional coupler with a forward and reverse coupled port. Variations of bi-directional couplers exist, called forward coupler and reverse coupler, which impact which of the coupled ports is coupled to the forward or reverse port.

It is important to note that the amount of coupling offered by a directional coupler directly impacts the theoretical minimum of the insertion loss of the main transmission path. The less coupled the ports, the lower the insertion loss. It is common for the coupled port to be rated at a lower power level than the main transmission path, and if the main transmission path power minus the couple strength exceeds the coupled ports power handling ability, failures can occur. Generally, a 3-port directional coupler with a precision internally matched termination will allow for higher directivity than a 4-port directional coupler with an external termination.

Another factor to consider is the type of termination at the terminated port of a directional coupler. If the termination is set to the intrinsic impedance of the transmission line, often 50 ohms, then the energy in that terminated port should be absorbed with minimum reflections. However, if the terminated port is a short, open, or a mismatch to the characteristic impedance of the transmission line, then the power at that port will be reflected back to the main transmission path. Moreover, if the terminated port power exceeds the power limits of the terminator, failures can occur. This could be especially bad if a matched terminated port fails becomes a reflective load, leading to damaging power levels on the main transmission path.

Directional couplers are commonly used in test and measurement applications. An example of this, is to use a bi-directional coupler, or perform multiple tests with a directional coupler, and measure the incident and reflected power through a transmission line. This will provide a measure of the VSWR, minus the losses associated with the coupler itself. Signal sampling, injection, and power flow monitoring, are other example applications, where a user must also account for the losses associated with the directional coupler for optimum accuracy.

Depending on the quality of the directional coupler, the isolation between the ports may also need to be considered when conducting accurate measurements. There is often some leakage between the ports, not associated with the intended coupling. This quantity is often referred to as isolation, which is a measure of how well the coupler design prevents leakage. The directivity of a directional coupler is a ratio of the isolation to the coupling factor, which is a common figure of merit for couplers.

As with most RF/microwave components, the exact measure of the parameters of a device are not absolutely consistent over frequency. The specified coupling factor, insertion loss, directivity, isolation, and etc. are usually all factors of frequency. This may need to be considered, along with any manufacturing tolerances, when conducting sensitive measurements. Directional couplers also have a bandwidth in which they operate, and there are design tradeoffs among the mentioned parameters, so the best coupler design ultimately depends upon the application.

There are some directional couplers which enable DC current to pass through. Many do not, as the ports are at DC ground. For those that do pass DC current, it is important to keep the current below the rated limit, as the resistive losses could cause heating, or affect the performance of the termination. Also, grounding all ports of a dual-directional coupler, or bi-directional coupler, is necessary to meet specified performance. The quality of the grounding and connection load is also important match with the port impedance of the directional coupler.

Hybrid couplers, either 90 degree or 180 degree hybrids, are also commonly referred to as “couplers”. These components intrinsically operate differently than directional couplers, though they often look similar in physical design. However, these devices provide a power splitting, 3dB split, between the output and coupled port, and could cause damage if confused for a directional coupler with much lower coupling factor.

The post Directional Coupler Do’s and Don’ts appeared first on Pasternack Blog.

Let’s be Open with a Load of Info about Coaxial Calibration Kits

Pasternack Blog -

Coaxial calibration kits (Cal-kits), or vector network analyzer (VNA) coaxial calibration kits, are indispensable tools for ensuring that a VNA is providing the most accurate measurements possible. Without regularly calibrating a VNA with quality termination components, the conditions in which a device under test (DUT) is testing will also be included in the test data. If these conditions are well known, then the data can be refined with additional processing. However, any unknown factors will still corrupt the data.

Hence, cal-kits are essential for removing the test cables, connectors, adapters, and other persistent influences from the valuable S-parameter, and other VNA, data taken at the point of calibration. Also, there are some cases where it may be beneficial to several high quality terminations for calibrating a DUT’s performance.

Commonly included in a coaxial calibration kit are precision shorts, opens, loads, and a thru adapter. These well-machined components are very different from typical terminations and standard adapters. The quality, impedance accuracy, and frequency performance of calibration kit terminations are generally vastly superior to standard terminations.

The shorts in a calibration kit “short” the energy emitted from the generators in a VNA, while an open appears as an unterminated transmission line end without allowing coupling and radiation to the external environment. The load in a calibration kit is chosen to match the transmission line and port impedance of the VNA and DUT. Lastly, the thru is a simple adapter that connects the two ports of a calibration kit, designed to be as close to an ideal transmission line as possible, hence invisible.

Cal-kits come in a variety of standard coaxial connector sizes, with N-type being among the most common. Many millimeter-wave applications are also driving the use of much higher frequency calibration kits, such as 3.5mm cal-kits, which often perform to 26.5 GHz. To account for the diversity of DUTs and coaxial cables, precision adapter kits are also very valuable accessories to calibration kits. A particularly helpful adapter may be a male/plug and female/jack adapter, which can be used to adapt the gender of the calibration component to connector and DUT ports with different genders than the native cal-kit component. It is important for these adapters to be of high quality, or any performance degradations will reduce the effectiveness of a quality calibration kit.

Moreover, leveraging precision adapters, though expensive, is usually a more cost effective solution for handling the wear and tear of use, than subjecting the cal-kit components to repeated mate/demate cycles. Other useful accessories include precision coaxial test cables. There are many varieties of these cables, whose value comes from their ability to appear “invisible” to the test setup. Lastly, torque wrenches, which are often included in a calibration kit, allow for a user to make consistent matings between coaxial connectors, thus enhancing consistency and repeatability.

Fortunately, coaxial calibration kits often come with attractive cases, which are both durable and offer sport padded organization slots for holding the valuable calibration components and accessories. Along with the cases, dust caps for each end of the calibration kit components prevent ingress from dust, other particulates, and water from settling inside the coaxial connector of the components. Many technicians will use dust-free air sprayers or electronics grade alcohol cleaning kits to further ensure a contamination free connection. These cleanliness efforts may also extend the lifespan of a calibration kit by preventing marring of the inner surfaces of a connector by hard particles grinding inside the connectors during mating.

The post Let’s be Open with a Load of Info about Coaxial Calibration Kits appeared first on Pasternack Blog.

The Difference between RF Amplifier Types

Pasternack Blog -

At first look, there are many different types of RF amplifiers, and it could be overwhelming to go from the specs you need to narrowing down what RF amplifier type is the best fit. Most RF amplifier types came about from the specification requirements of common transceiver, receiver, transmitter, radar, and modulation circuits and system-level typologies. The following is a brief overview of the purpose of these amplifiers, with insights into the applications they may be a good fit for.

Broadband Amplifiers

Broadband amplifiers, or wideband amplifiers, are designed to offer moderate gain over a wide bandwidth, while maintaining a low noise figure. These types of amplifiers are often used within receiver circuitry at the front-end of the antenna, when low noise amplifiers aren’t required, and within a receiver where additional gain is needed and noise is a concern.

Gain Block Amplifiers

Gain block amplifiers, or gain blocks, are similar to broadband amplifiers, with the exception that they typically aren’t designed for as low of a noise figure and have greater gain than broadband amplifiers. Gain block amplifiers are used in IF, RF, and microwave transmitter applications, and may include models with narrow bandwidths or wide bandwidths. This typically depends on the types of applications they are designed for.

Log Amplifiers

A log amplifier is an amplifier that exhibits a gain curve where the output voltage is a multiple of the natural log of the input voltage. This type of amplifier is specifically used in applications that require this behavior.

Variable Gain Amplifiers

Variable gain amplifiers are a type of amplifier with a controllable, and sometimes programmable, gain. This can be done through the use of variable gain circuits, or variable attenuators and a fixed gain amplifier, depending on the application. Also known as linear-to-logarithmic converters, these amplifiers are often used as part of a closed-loop control circuit to maintain a consistent signal power level of the main signal path.

Low Noise Amplifiers

Low noise amplifiers leverage any portion of a transmitter or receiver design where a low power signal needs to be amplified to a working power level without introducing significant noise or phase noise. This could be at the output of an oscillator, strengthening a signal to drive a mixer, or at the input of an antenna to increase a signal’s power enough to be easily processing by demodulation and digitization circuitry.

Coaxial and Waveguide Power Amplifiers

Power amplifiers are the workhorse amplifiers in the RF front-end of transmitters, which convert the small power signals from communications and radar equipment to high powered transmissions sent to an antenna. The goal of a power amplifier is to increase the gain of a signal to a high power level, without reducing the quality of the signal. As this is typically a hard design challenge with many tradeoffs, certain power amplifiers may be optimized for parameters that best fit the pulsed radar, CW radar, digital communications, or other application for which they are required.

Power amplifiers must also contend with handling various types of loads, some of which could cause damaging reflections. Hence, power amplifier designs commonly include protective circuitry. Power amplifiers could leverage coaxial connectors, or even waveguide connectors if the power level is high enough or the frequency of operation is high enough.

Learn more, here {https://blog.pasternack.com/active-components/rf-amplifiers-active-components/rf-amplifier-packaging-thermal-dynamics/}

And here {https://blog.pasternack.com/rf-amplifiers/rf-amplifier-power-gain-considerations/}

Linear Amplifiers

A linear amplifier is typically a type of RF power amplifier, which is specifically designed to provide highly linear performance, with the input and output maintaining a proportional linear relationship. Hence, linear amplifiers are designed to optimize linearity over other design considerations, especially under a wide range of load conditions. Linear amplifiers are most often used in transmitters and test equipment where high linear power is required.

Bi-directional Amplifiers

Bi-directional amplifiers are a combination of both a transmitter and a receiver, designed for the purpose of acting as an intermediate node receiving a weak signal and amplifying that signal for retransmission and capture at an electrically distant location. Bi-directional amplifiers are often used to extend communications networks to remote locations without having to install additional infrastructure. This could be for covering larger overland areas, or used with coaxial transmission lines to extend a signal or communication system longer distances underground or within facilities. Bi-directional amplifiers usually require good performance low-noise amplifiers and power amplifiers. With models that handle high throughput digital communications, the necessary demodulation and modulation circuitry may be included in a bi-directional amplifier to completely recreate and retransmit a signal to ensure the highest fidelity at the destination.

Learn more, here {https://blog.pasternack.com/uncategorized/constraints-considerations-bi-directional-amplifiers/}

And here {https://blog.pasternack.com/active-components/rf-amplifiers-active-components/bi-directional-amplifiers-just-facts/}

Hi-Rel Amplifiers

Hi-Rel amplifiers are a class of amplifiers that meet, or exceed, a high reliability standard or expectation, typically for automotive, aerospace, space, or military/defense applications. These amplifiers are often more resilient than their standard counterparts, and have ratings that include the likely lifespan of the amplifier under a variety of operational conditions.

Learn more, here {https://blog.pasternack.com/uncategorized/whats-hype-high-reliability-hi-rel/}

 

The post The Difference between RF Amplifier Types appeared first on Pasternack Blog.

How to Accessorize Your Coaxial Cable and Connector

Pasternack Blog -

In the case of test and measurement, cable and connector installations, and coaxial assemblies, there is substantial design effort and thought dedicated to selecting the optimal coaxial cables and connectors for the project. These factors include electrical properties, mechanical properties, infrastructure logistics, pricing, environmental ratings, and standards and qualifications.

However, there is more to a coaxial assembly and installation than just the cables and connectors. These handy RF tools must be installed with hardware and components that ensure good RF operation and electrical isolation. Additionally, maintenance is also a common occurrence, and there are tools that are necessary to perform field and factory repairs to these system. This post will briefly walk through several coaxial cable and connector accessories and assembly/repair tools that are frequently used to ensure proper device and system operation over the lifetime of the project.

EMI/RFI Gaskets

Though the shielding of a coaxial cable assembly provides a high isolation against invasive signals from the surrounding environment, the connections between the bulkhead connector and housing aren’t always as well shielded. Hence, EMI/RFI gaskets can be used to ensure a complete seal of the bulkhead connector and the metallic housing of a coaxial assembly, which can provide a higher level of isolation of the overall assembly.

Depending on the type of connector format, both ring and flat gaskets are available. For example, with SMA gaskets, flat 4 hole flange connector gaskets are common, as well as ring gaskets.

Nuts & Bolts

Many bulkhead, or flange, coaxial connectors require nuts and bolts to connect to an assembly. Often, knowing the exact type, size, and threading of the screw is necessary to properly connect the flange to a housing. Material composition for these screws is sometimes very important, as certain environmental factors can cause galvanic corrosion, or other deterioration effects, which may eventually reduce device/system performance or cause failures. Fasteners are a common failure mode for complex assemblies and systems.

Brackets and Other Hardware

The mechanical stresses that inline coaxial components undergo can be significant. Typical coaxial cables and connectors are design for a certain level of acceptable stress, but any break in the line for an inline component can concentrate those stresses in that point of non-continuity. Hence, brackets, ties, and other supporting structures are often valuable to ensure consistent placement and reduces stresses at those critical junctions.

Dust Caps With/Without Chains

Be it indoors or outdoors, dust and particulate debris can be an issue with any coaxial system. Any particles inside a coaxial connector or line can reduce the RF performance and even lead to sparking and failure at high power levels. With the nature of RF energy, even coaxial ports of an assembly that go unused need to be properly terminated to avoid interaction with the outside environment and environmental or interference ingress.

Coaxial connector dust caps were specifically designed to provide an additional level of environmental protection compared to standard terminations. Also, many of these dust caps can provide shorting or non-shorting terminations, depending on the electrical requirements of a specific port. Moreover, some dust caps are available with security chains to prevent loss and damage of the cap if a port requires frequent access.

The post How to Accessorize Your Coaxial Cable and Connector appeared first on Pasternack Blog.

Online DSP Classes: Why Such a High Dropout Rate?

Rick Lyon's Blog on DSPRelated -

Last year the IEEE Signal Processing Magazine published a lengthy article describing three university-sponsored online digital signal processing (DSP) courses [1]. The article detailed all the effort the professors expended in creating those courses and the courses' perceived values to students. 

However, one fact that struck me as important, but not thoroughly addressed in the...

Platform interference

The EMC Blog -

Every manufacturer seemingly wishes to add some form of wireless capability into new and existing mobile, household, industrial, scientific, and medical product. This trend toward the “Internet of Things” is in full swing and with it comes problems with EMI. That is, EMI from the product itself, that interferes with sensitive telephone, GPS/GNSS, and Wi-Fi/Bluetooth receivers. This is called “platform interference” and it’s a big problem for manufacturers.

Review: Tekbox LISNs

The EMC Blog -

Tekbox Digital Solutions recently introduced LISN models for both line-operated and DC-operated equipment. I’ll be reviewing their model TBLC08 (line-powered 50uH LISN) and model TBOH01 (DC 5uH LISN).

Review: Tekbox Near-Field Probes

The EMC Blog -

A set of near-field probes is an essential tool for troubleshooting EMI issues. Tekbox Digital Solutions has recently introduced a kit containing a set of three H-field, one E-field probe, and either a 20 or 40 dB gain broadband preamplifier. All this is included in a laser-engraved wooden box - a very nice touch. The probes may also be ordered without the preamplifier. I had a chance to try them out and compare with some similar probes.

Pages

Subscribe to www.rfmentor.net aggregator - Editor's Picks