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This material, coming into use for various application, has significant potential. The exam cites use in MMICs, Monolithic Microwave Integrated Circuits at the highest frequencies. If you want to read more, this material used in High-electron-mobility transistor (HEMT), aka heterostructure FET (HFET), aka modulation-doped FET (MODFET). Other applications are in power control circuitry for electric vehicles, and a range of high intensity LEDs. The aforementioned high electron mobility is in fact an "important" property to make it useful at UHF and beyond.
MMICs are Monolithic Microwave Integrated Circuits, which operate as signal and power amplifiers across a set bandwidth, with consistent gain. They typically have have 50 ohms input and output impedance.
Power is typically applied to the output, via a resistor or inductor. The inductor conducts DC power, while preventing RF or microwave energy going to the power supply.
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| Image and diagram indicating the use of a MMIC, by WikiMedia user: Appaloosa. |
Similar devices, such as the MAR-6, can be used in TV masthead amplifiers.
A preamplifier is useful in weak signal stations, especially when placed as close to the antenna feed-point as practical. This is especially relevant for EME (moonbouce) statsions. However, adding a preamplifier to a receive signal chain always adds a small amount of noise.
It is the decibel ralationship of the the input and output signal-to-noise ratios.
You can see the maths at: Wikipedia: Noise figure. Many EME pages have information on preamplifiers and signal and noise levels, etc.
The examiner uses a perhaps slightly optimistic 0.5 dB figure.
Several hundred euro buys a 0.68 dB NF unit, the previous
Dual In-line Packages are often used to house intergrated circuits. They are termed DIP, or occasionally, DIL. They have a row of leads, usually spaced at 0.1" or 2.54 mm down each side. Plastic is most common, although ceramic material can be used, which is better for dissipating heat.
They are most usually mounted by inserting the pins through a printed ciruit board, and soldering them in place. Socketing is an alternative.
While there are FM broadcast band receiver ICs in these packages, at UHF, the length of the pin, and the internal conductor leading to the silicon die becomes too long.
Opto-couplers are also mounted in these packages, as are arrays of resistors or Darlington transistors.
The width is 0.3" in lower pin counts, 0.6" in high counts (40 pins for the Z80 and 8080, fewer for many EPROMS), and 0.9" wide 64 pin monsters for the 68000 processor. 0.3" wide 24 and 28 pin items are termed "SkinnyDIP". CDIP or CerDIP may be used to specify Ceramic DIP, be they white or dark grey. PDIP specifies plastic, black except for white opto-couplers / opto-isolaters.
ShrinkPDIP have a 0.07 in or 1.778 mm lead pitch.
Resistor arrays are often in fawn or blue packages, or occasionally white. Small relays and switches are also available in DIP sizes.
Almost all modern commercial electronics is built using surface mount components. In many case the components are significantly smaller, and lower in profile, than through-hole ones. Track and lead lengths can be much shorter than on through-hole boards, making the useful frequency extend into the UHF range.
To further extend the frequency range into the microwave region, microstrip boards have tracks with tuned widths, above a ground plane, to ensure the correct impedance.
These are the same thing. The dual names are because they can couple an electrical signal between two circuit sections, while electrically isolating them. They can be used in low voltage equipment controlling mains powered circuits, or between mains powered equipment and telecommunications equipment, to remove the risk of dangerous voltages appearing on the 'phone line, where they could harm technicians and line workers.
Common types consist of a LED, often and infra-red one, which illuminates a photodiode or phototransistor. Current into the LED results in a small voltage or the conduction of the phototransistor on the output side.
While various materials are used for solar cells, Silicon is used on standard panels you might use for a field day or emergency activation.
When light strikes the material electrons are forced to move, creating current. Each cell only generates 0.5 volts (or slightly more, at 0.55 volts), so many need to be places in series to generate useful voltages. Open circuit voltage is often significantly above the voltage of the battery to be charged.
These have moved from an expensive way to generate power, used in things like remote microwave repeater stations to the cheapest way to generate power, and rapid to market. While a nuke plant may take 50 years from proposal to first syncronisation to the grid (yes, Hinkley Point C was proposed in 1981, and with a lot of luck may come online in 2031), grid scale solar fields can be online within a year or so, and provided shade and often improved grass for sheep grazing on otherwise marginal land.
While panels for Ham use likely only output tens of volts when open circuit, rooftop ones can output hundreds, especially when in a series string - they may be "just DC", but they could be lethal if mishandled. That said, industry standard connectors are touchproof in male and female form.
Remote repeaters use panels, but perhaps your club can get a grant to make your city based repeater grid independent, also saving on or removing power charges. MMPT charge controllers are typically used in such cases.
The University of New South Wales in Sydney, Australia is one of the global leaders in solar, including ones under 10 cm in diameter which work by having light concentrated on them using many large mirrors.
The US's research agency is the National Renewable Energy Laboratory, which was established as the Solar Energy Research Institute under the Solar Energy Research, Development and Demonstration Act of 1974, passed under Gerald Ford.
Even if developments mean CdTe becomes more common, the answer will remain Silicon on the paper for the remainder of this exam period.
Photoconductive materials, exhibit a considerable reduction in resistance when illuminated, (otherwise termed an increase in conductivity). It appears the examiner is interested in photodiodes, or perhaps photostransisters, as they are indicate that photoconductive devices are most commonly made using a crystalline semiconductor. The type of semiconductor used determines the spectrum detected.
An alternative material used in light dependent resistors (LDRs) is CdS, which only appears in a spoiler on a PV question.
These are the actual questions from the Extra licence exam pool, as published by the NCVEC.
E6E01
Why is gallium arsenide (GaAs) useful for semiconductor devices operating at UHF and higher frequencies?
A. Higher noise figures
B. Higher electron mobility
C. Lower junction voltage drop
D. Lower transconductance
GaAs material has higher electron mobility, answer B.
E6E02
Which of the following device packages is a through-hole type?
A. DIP
B. PLCC
C. BGA
D. SOT
DIP stands for Dual-In-Line Package (also called DIL), these have been used for ICs, resistor arrays, and Darlington arrays for many decades, and are through-hole components, answer A.
The remainder are surface-mount.
E6E03
Which of the following materials supports the highest frequency of operation when used in MMICs?
A. Silicon
B. Silicon nitride
C. Silicon dioxide
D. Gallium nitride
This is the relatively new material, Gallium Nitride, GaN, answer D.
E6E04
Which is the most common input and output impedance of MMICs?
A. 50 ohms
B. 300 ohms
C. 450 ohms
D. 75 ohms
The standard RF communications system impedance is 50 ohms, and this applies to MMICs, answer A.
E6E05
Which of the following noise figure values is typical of a low-noise UHF preamplifier?
A. 0.5 dB
B. -10 dB
C. 44 dBm
D. -20 dBm
0.5 dB, answer A.
Interestingly this has improved over the figure supplied 4 years earlier.
E6E06
What characteristics of the MMIC make it a popular choice for VHF through microwave circuits?
A. The ability to retrieve information from a single signal even in the presence of other strong signals
B. Extremely high Q factor and high stability over a wide temperature range
C. Nearly infinite gain, very high input impedance, and very low output impedance
D. Controlled gain, low noise figure, and constant input and output impedance over the specified frequency range
Unlike simple RF transistors, MMICs simplify RF device design by having controlled gain, a low noise figure, and constant input and output impedance over the design frequency range, answer D.
E6E07
What type of transmission line is used for connections to MMICs?
A. Miniature coax
B. Circular waveguide
C. Parallel wire
D. Microstrip
Microwave circuit boards, including those using MMICs, use microstrip construction, answer D.
E6E08
How is power supplied to the most common type of MMIC?
A. Through a capacitor and RF choke connected to the amplifier input lead
B. MMICs require no operating bias
C. Through a resistor and/or RF choke connected to the amplifier output lead
D. Directly to the bias voltage (Vcc) lead
Power is supplied via a resistor and/or RF choke, connected to the amplifier output lead, answer C.
E6E09
Which of the following component package types have the least parasitic effects at frequencies above the HF range?
A. TO-220
B. Axial lead
C. Radial lead
D. Surface mount
Surface mount is most suitable for VHF and UHF circuits, answer D.
E6E10
What advantage does surface-mount technology offer at RF compared to using through-hole components?
A. Smaller circuit area
B. Shorter circuit board traces
C. Components have less parasitic inductance and capacitance
D. All these choices are correct
Surface mount uses components without leads, soldered directly to the PCB, reduces parasitic inductance and capacitance, answer D.
E6E11
What is a characteristic of DIP packaging used for integrated circuits?
A. Extremely low stray capacitance (dielectrically isolated package)
B. Extremely high resistance between pins (doubly insulated package)
C. Two chips in each package (dual in package)
D. Two rows of connecting pins on opposite sides of package (dual in-line package)
These have 2 rows of pins, one down each side of the package, answer D.
E6E12
Why are DIP through-hole package ICs not typically used at UHF and higher frequencies?
A. Excessive dielectric loss
B. Epoxy coating is conductive above 300 MHz
C. Excessive lead length
D. Unsuitable for combining analog and digital signals
The lead length, and the internal lead frame connections are excessively long at UHF and up, answer C.
E6F01
What absorbs the energy from light falling on a photovoltaic cell?
A. Protons
B. Photons
C. Electrons
D. Holes
Light striking the photovoltaic material strikes the electrons, causing current flow, answer C.
E6F02
What happens to photoconductive material when light shines on it?
A. Resistance decreases
B. Resistance increases
C. Reflectivity increases
D. Reflectivity decreases
Resistance decreases when the material is illuminated, answer A.
E6F03
What is the most common configuration of an optoisolator or optocoupler?
A. A lens and a photomultiplier
B. A frequency modulated helium-neon laser
C. An amplitude modulated helium-neon laser
D. An LED and a phototransistor
This couples data or other information between circuits while providing electrical isolation. These typically consist of an LED and a phototransistor, answer D.
The others are just plain silly.
E6F04
What is the photovoltaic effect?
A. The conversion of voltage to current when exposed to light
B. The conversion of light to electrical energy
C. An optical computing device in which light is coupled between devices by fiber optics
D. The effect that causes a phototransistor’s beta to decrease when exposed to light
This is the conversion of light energy to electrical energy, answer B.
E6F05
Which of the following describes an optical shaft encoder?
A. A device which detects rotation of a control by interrupting a light source with a patterned wheel
B. A device which measures the strength of a beam of light using analog to digital conversion
C. A digital encryption device often used to encrypt spacecraft control signals
D. A device for generating RTTY signals by means of a rotating light source
These detect rotation by having a patterned disc interrupt an optical path answer A.
While they can be used for sensing in industrial applications, in Amateur Radio they are used for the tuning knob on transceivers. They were also used ball-based PC mice.
E6F06
Which of these materials is affected the most by photoconductivity?
A. A crystalline semiconductor
B. An ordinary metal
C. A heavy metal
D. A liquid semiconductor
This is a crystalline semiconductor, answer A.
E6F07
What is a solid-state relay?
A. A relay using transistors to drive the relay coil
B. A device that uses semiconductors to implement the functions of an electromechanical relay
C. A mechanical relay that latches in the on or off state each time it is pulsed
D. A semiconductor switch that uses a monostable multivibrator circuit
An SSR uses an optocoupler (LED controlling a phototransistor or photodiode) connected to a high current semiconductor to emulate a regular relay, answer B.
E6F08
Why are optoisolators often used in conjunction with solid state-circuits when switching 120 VAC?
A. Optoisolators provide a low-impedance link between a control circuit and a power circuit
B. Optoisolators provide impedance matching between the control circuit and power circuit
C. Optoisolators provide an electrical isolation between a control circuit and the circuit being switched
D. Optoisolators eliminate the effects of reflected light in the control circuit
These provide good electrical isolation between the low voltage circuit, and the mains voltage circuit, answer C.
E6F09
What is the efficiency of a photovoltaic cell?
A. The output RF power divided by the input DC power
B. The output in lumens divided by the input power in watts
C. The open-circuit voltage divided by the short-circuit current under full illumination
D. The relative fraction of light that is converted to current
This is the fraction (percentage) of light energy converted to electrical energy (current), answer D
E6F10 (B)
What is the most common type of photovoltaic cell used for electrical power generation?
A. Selenium
B. Silicon
C. Cadmium Sulfide
D. Indium arsenide
Ordinary roof-top solar panels are silicon, answer B.
E6F11
What is the approximate open-circuit voltage produced by a fully-illuminated silicon photovoltaic cell?
A. 0.5 volts
B. 0.7 volts
C. 1.1 volts
D. 1.5 volts
These generate half a volt per cell, answer A, so many are placed in series to generate a useful voltage.
On to: Practical Circuits 1 - Digital circuits & Amplifiers
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Written by Julian Sortland, VK2YJS & AG6LE, August 2025.
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