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Week 1 TechNet 09-11-2019
#1
We had eight check-ins:
KC1KQH, John in Cheshire
W1YSM, Ed in Wallingford
NZ1J, Dave in Northford
KC1NF, Nancy in Northford
WA1JKR, John in Southington
KC1HWX, Victor in Wallingford
N1YLN, Ed in Waterbury
N1GNV, John in Meriden
Net Control was K1RCT, Rob in Meriden

The Subject was power supplies and the licensing topic (from the 2019-2022 General Pool) was power supplies. The script was as follows.

The Technical Topic of the Week is Power Supplies.
This week’s topic supplied by K1VDF, John Blevins.

There are many types of Supplies in-use but primarily only two types of power supplies commonly used by Radio Amateurs.
Linear Supplies and Switching Supplies.

First; Linear:
A linear regulated supply is a transformer based power supply with a transistor regulator. A typical linear regulator is designed to output a fixed voltage for a wide range of input voltages and it simply drops any excess input voltage to allow a maximum output voltage to the load. These supplies are typically heavy in weight due to the transformer converting AC line voltage to a smaller voltage which becomes rectified into a DC Voltage. If the input voltage gets too low, the transistor circuit will lose regulation, meaning that it will fail to keep the voltage steady. Linear regulated power supplies are rather inefficient but they are typically very clean with very little noise or ripple current. Also, to get rid of all that heat they have to use large heat sinks which make them large, heavy, and expensive. Linear power supplies are probably the most common of supplies.

Second; Switching:
A switching supply realizes the advantages of linear regulated designs which are reliable & clean with a small, efficient, and cheaper package. Switching power supplies rectify the incoming AC power line voltage into DC, re-convert it into high-frequency square-wave, step that AC voltage up or down by using a lightweight transformer, then rectify the transformer’s AC output into DC and filter the final output. Voltage regulation is achieved by altering the “duty cycle” of the DC-to-AC inversion on the transformer’s primary side. They are lighter because of a smaller transformer core. Switchers have another big advantage over the other designs: they can be made so totally independent of the input voltage that it can work on any electric power system in the world; these are called “universal” power supplies.

The downside of switchers is that they are more complex & tend to generate a lot of high-frequency AC “noise” on the power line. Many low-quality switchers also have significant ripple voltage on their outputs.
Expensive switchers are ripple-free and have noise nearly as low as for some a linear types & tend to be as expensive as linear supplies. The reason to use an expensive switcher instead of a good linear is if you need universal power system compatibility, a smaller footprint or higher efficiency.

License Exam Questions concerning Power Supplies.
(Correct answers are in CAPITALS).

“Exam Question ID number: G7A08” (C)
“Which of the following is an advantage of a switchmode power supply as compared to a linear power supply?
• A.
• B.
• C. HIGH-FREQUENCY OPERATION ALLOWS THE USE OF SMALLER COMPONENTS
• D.
<The following Exam Questions for reference only>

G7A04 (A)
What is an advantage of a half-wave rectifier in a power supply?
• A. ONLY ONE DIODE IS REQUIRED
• B. The ripple frequency is twice that of a full-wave rectifier
• C. More current can be drawn from the half-wave rectifier
• D. The output voltage is two times the peak output voltage of the transformer

G7A01 (B)
What useful feature does a power supply bleeder resistor provide?
• A. It acts as a fuse for excess voltage
• B. IT ENSURES THAT THE FILTER CAPACITORS ARE DISCHARGED WHEN POWER IS REMOVED
• C. It removes shock hazards from the induction coils
• D. It eliminates ground loop current

G7A02 (D)
Which of the following components are used in a power supply filter network?
• A. Diodes
• B. Transformers and transducers
• C. Quartz crystals
• D. CAPACITORS AND INDUCTORS

G7A05 (B)
What portion of the AC cycle is converted to DC by a half-wave rectifier?
• A. 90 degrees
• B. 180 DEGREES
• C. 270 degrees
• D. 360 degrees

G7A06 (D)
What portion of the AC cycle is converted to DC by a full-wave rectifier?
• A. 90 degrees
• B. 180 degrees
• C. 270 degrees
• D. 360 DEGREES

G7A07 (A)
What is the output waveform of an unfiltered full-wave rectifier connected to a resistive load?
• A. A SERIES OF DC PULSES AT TWICE THE FREQUENCY OF THE AC INPUT
• B. A series of DC pulses at the same frequency as the AC input
• C. A sine wave at half the frequency of the AC input
• D. A steady DC voltage
K1RCT - Rob
W1NRG Station Activities Manager
Home Email

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#2
I listened into the first TechNet. Here are my comments.

The upfront query allows anyone with imminent needs to be recognized. The net controller can decide whether to allow for discussion, arrange for interested parties to contact each other after the net, or add a subject to a future net.

Encouraging to see two KC1’s in attendance along with experienced members having strong technical background present to help as needed.

Having one subject (power supplies) enables in-depth discussion that is very educational, especially in that it relates to license examination questions.
Reply
#3
Thanks for the feedback, John. It is most appreciated.
K1RCT - Rob
W1NRG Station Activities Manager
Home Email

Reply
#4
Net Control: N1ZN
Topic: VHF & UHF Operation

Check ins: K1LHO, W1YSM, K1LYP, K1RCT, W1NNZ, N1GNV, KC1KQH, KB1TJD, W1POP, KB1FYL

Discussion Highlights:
- Bands: 6 Meters, 2 Meters, 70cm - side band as opposed to FM
- Calling Frequencies: 50.125, 144.200, 432.100 MHz
- Antennas: Beams and verticals
- Propagation: F-Layer Skip and Sporadic E
- Grid Squares: 4 Digit (example: FN31) and 6 Digit (FN31nk)
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