Deep Dive: T6A08
The correct answer is C: A single circuit is switched between one of two other circuits. The function of an SPDT (Single-Pole Double-Throw) switch is to switch a single circuit between one of two other circuits. An SPDT switch has one input (pole) that can be connected to either of two outputs (throws). SPDT switches have three terminals: one common terminal (pole) and two output terminals (throws). The switch connects the common terminal to one of the two output terminals. This allows you to switch a single circuit between two different paths. SPDT switches are commonly used for selecting between two antennas, switching between two power sources, or routing signals to different destinations. They're essential for circuit control and signal routing in radio equipment.
Why Other Answers Are Wrong
Option A: Incorrect. A single circuit opened or closed describes an SPST (Single-Pole Single-Throw) switch, not an SPDT. SPDT switches have two output positions, not just on/off. Option B: Incorrect. Two circuits opened or closed describes a DPST (Double-Pole Single-Throw) switch, not an SPDT. SPDT has one pole, not two. Option D: Incorrect. Two circuits each switched between one of two other circuits describes a DPDT (Double-Pole Double-Throw) switch, not an SPDT. SPDT has one pole, not two.
Exam Tip
SPDT = One input, two outputs. Remember: SPDT (Single-Pole Double-Throw) switches a single circuit between one of two other circuits - one pole, two throws.
Memory Aid
**S**PDT = **S**ingle **P**ole, **D**ouble **T**hrow (think 'SPDT = 1 pole, 2 throws')
Real-World Example
You're setting up your station with two antennas. You use an SPDT switch to select between them. The switch has one input (from your transceiver) and two outputs (one to each antenna). You can switch between the two antennas, but only one is connected at a time. This is the function of an SPDT switch.
Source & Coverage
Question Pool: 2022-2026 Question Pool
Subelement: T6A
Reference: 2022-2026 Question Pool · T6 - Electrical components
Key Concepts
Verified Content
Question from the official FCC Technician Class pool. Explanation reviewed by licensed amateur radio operators and mapped to the T6A topic.