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G6B

CIRCUIT COMPONENTS

- Analog and digital integrated circuits (ICs); microwave ICs (MMICs); display devices; RF connectors; ferrite cores

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G6B011 of 11

What determines the performance of a ferrite core at different frequencies?

Why Ferrite is a ceramic made by sintering iron oxide with other metal oxides such as nickel, zinc or manganese, and the exact recipe, called the mix, sets the material's permeability and loss characteristics versus frequency. A high permeability manganese-zinc mix (like mix 31 or 75) works well at low HF for common-mode chokes, while lower permeability nickel-zinc mixes (like 43 or 61) are chosen for upper HF and VHF. Choosing the wrong mix can make a choke nearly useless or cause it to overheat, so catalogs list a recommended frequency range for each mix number.
Watch out Physical dimensions such as thickness or the diameter ratio affect how much inductance a given core produces and how much power it can handle, but they do not change the frequency range where the material is effective.
Ferrite mix number = frequency range. Low mix numbers like 31 for low HF, 43/61 for higher bands.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
G6B022 of 11

What is meant by the term MMIC?

Why MMIC stands for Monolithic Microwave Integrated Circuit. "Monolithic" means the whole amplifier, including its matching and bias networks, is fabricated on a single chip of semiconductor material (often gallium arsenide), and "microwave" reflects that these devices are built to work at UHF and microwave frequencies. A typical MMIC is a small gain block with 50 ohm input and output impedances, so it needs only a DC bias resistor and blocking capacitors to become a working amplifier stage.
Watch out Choices built around "multi-mode" or "mode modulated" borrow radio operating terminology that has nothing to do with chip construction; MMIC describes how and where the device is made, not what modulation it handles.
MMIC = Monolithic Microwave IC: one chunk of chip, microwave gain block, 50 ohms in and out.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
G6B033 of 11

Which of the following is an advantage of CMOS integrated circuits compared to TTL integrated circuits?

Why CMOS logic uses complementary pairs of P-channel and N-channel MOSFETs, so in either steady logic state one transistor is off and essentially no current flows from supply to ground. Current is drawn mainly during switching transitions to charge and discharge capacitance. TTL uses bipolar transistors with resistive paths that draw steady current whether or not the output is changing, so CMOS is dramatically more power efficient, which also means less heat and longer battery life.
Watch out High power handling is not it: CMOS logic gates are small-signal digital devices, and the choices about RF amplification and power supply regulation describe entirely different analog part families, not a logic family comparison.
CMOS = Complementary MOS = Conserves Milliwatts. Only burns power when it switches.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
G6B044 of 11

What is a typical upper frequency limit for low SWR operation of 50-ohm BNC connectors?

Why BNC is a small bayonet-lock coaxial connector with a controlled 50-ohm geometry, so it holds a good match well up into the microwave region. The pool's figure for low SWR operation of the 50-ohm BNC is about 4 GHz. Above that, the connector's internal dimensions start to allow moded behavior and the match degrades, so precision types like SMA or N are used instead.
Watch out The 500 MHz figure is the common practical ceiling quoted for the UHF (PL-259/SO-239) connector, which is not a constant-impedance design; 40 GHz belongs to tiny precision connectors such as 2.92 mm.
BNC = 4 GHz, UHF/PL-259 = a few hundred MHz. Small bayonet, big bandwidth.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
G6B055 of 11

What is an advantage of using a ferrite core toroidal inductor?

Why A toroid with a ferrite core wins on three counts at once. The high permeability of ferrite multiplies the inductance, so you get many millihenries from relatively few turns compared with an air-core coil. Ferrite is made in many mixes, each with a permeability and loss characteristic tailored to a particular frequency range, so you can pick a mix for HF, VHF or EMI suppression. And because the core is a closed magnetic loop, nearly all the flux stays inside it, which means little stray coupling to nearby parts and little pickup from them.
Watch out Each single-item choice is true on its own, so picking just one leaves out two equally valid advantages; the pool wants the combined answer.
Toroid = more L, chosen mix, contained field. Three benefits, so 'all of these'.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
G6B066 of 11

What kind of device is an integrated circuit operational amplifier?

Why An operational amplifier is a high-gain DC-coupled amplifier that works with continuously varying voltages, amplifying, summing, integrating or filtering signals whose values can take any level within the supply rails. That continuous, non-quantized behavior is the definition of an analog device, in contrast to circuits that only recognize discrete high and low logic states.
Watch out Calling it digital confuses it with logic gates and counters, which respond only to two voltage states; MMIC refers specifically to a monolithic microwave IC used at RF/microwave frequencies, not a general purpose op-amp.
Op-amp = smooth, continuous voltages = analog. Gates and logic = only 1s and 0s = digital.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
G6B077 of 11

Which of the following describes a type N connector?

Why The type N is a threaded, constant-impedance coaxial connector with a gasket seal, so it keeps water out and maintains a controlled 50-ohm (or 75-ohm) geometry well up into the microwave region, commonly rated useful to about 10 GHz. That combination of weather sealing and low loss at high frequency is why it is the standard choice for outdoor antenna and microwave feedline connections, where a UHF/PL-259 connector would be too lossy and too leaky.
Watch out The small bayonet-style connector described in one choice is the BNC, which twists on with a quarter turn and is typically used up to a few GHz at low power; the PL-259 answer is wrong because type N is a completely different design, not a plated variant of it.
N for Neill, and think 'N = Nice and Number 10': weatherproof, good to 10 GHz.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
G6B088 of 11

How is an LED biased when emitting light?

Why An LED is a diode, so current only flows when the anode is positive relative to the cathode, which is forward bias. Electrons and holes recombine across the junction and release energy as photons, so light output is proportional to forward current. Typical LEDs drop roughly 1.5 to 3 volts depending on color, so a series resistor is used to set the current, commonly 10 to 20 mA.
Watch out Reverse bias blocks current in an ordinary diode and produces no light; that condition belongs to Zener diodes, which are deliberately run in reverse breakdown as voltage references, not as light sources.
LED = Light Emitting Diode: light only when current flows forward, just like any conducting diode.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
G6B109 of 11

How does a ferrite bead or core reduce common-mode RF current on the shield of a coaxial cable?

Why A ferrite bead slipped over the coax acts as a common-mode choke: the ferrite's high permeability raises the inductance, and its lossy nature adds resistance, so the outside of the shield sees a large series impedance at RF. Since the current on the outer surface of the shield has to push through that impedance, it drops (I = V/Z). The desired signal inside the coax is differential (equal and opposite currents on center conductor and shield interior), its fields cancel inside the cable, so the ferrite has no effect on it.
Watch out The cancellation idea is tempting because chokes and cancellation both suppress noise, but a ferrite is a passive lossy inductor, not a device that generates an out-of-phase current; and nothing converts common mode into differential mode. Expelling magnetic fields describes a superconductor, not ferrite, which concentrates flux.
Ferrite = choke, not canceller. It adds impedance in series with the shield's outside surface.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
G6B1110 of 11

What is an SMA connector?

Why SMA stands for SubMiniature version A, a small screw-on (threaded) coaxial connector with a 50 ohm impedance. Because the threaded coupling keeps a precise, tight connection and the connector is physically small, it maintains good performance well into the microwave region, commonly specified to 18 GHz. You will find SMA connectors on handheld transceiver antennas, test cables, and GHz-range modules and MMIC boards.
Watch out The letters are not an acronym for a signaling scheme, so 'serial multiple access' is invented; and SMA threads on rather than pushing on, and it is a low-power RF connector, not a high-voltage one.
SMA = SubMiniature A: small, screws on, good for several GHz.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
G6B1211 of 11

Which of these connector types is commonly used for low frequency or dc signal connections to a transceiver?

Why RCA phono jacks are the standard on the back panel of transceivers for audio in/out, keying lines, PTT, ALC, and other low frequency or DC control connections. They are cheap and easy to terminate but have no controlled impedance and poor shielding, so they are not used for RF feedline work. The three other choices are all coaxial RF connectors designed to maintain a 50 ohm impedance.
Watch out PL-259 (the UHF connector) is the common HF antenna connector and BNC is used for VHF/UHF and test gear, but both are RF connectors, not audio or control connections; Type N is good well into the microwave range.
RCA = stereo/audio style plug on the back panel: audio, keying, ALC. The other three are coax RF.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
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