DC Power Injection on Telephone Lines
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Solution Overview
Problem
Existing systems for carrying power over active telephone lines face limitations in power capacity and interference issues, particularly with AC power transmission, and require complex filtering circuits, while DC power transmission is restricted to low power levels.
Innovation Solution
The system separates AC and DC signals in the subscriber loop, allowing a DC signal of any voltage level to be imposed on the wiring independently of the PBX/CO's DC characteristics, using AC Pass/DC Stop and DC Pass/AC Stop devices, and includes an off-hook detection mechanism to maintain telephone functionality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If AC power is transmitted over telephone lines, then power delivery capability is improved, but signal interference increases and complex filtering circuits are required
Solution Approach 1:
The patent segments the power transmission into different frequency components by separating AC and DC signals. The AC power signal is frequency-modulated to a high frequency carrier wave, allowing it to coexist with voice signals in the low frequency range. This segmentation of frequency spectrum resolves the contradiction by enabling power delivery while maintaining signal integrity through frequency division multiplexing.
Solution Approach 2:
The patent introduces an intermediary frequency-modulation process that converts direct AC power signals into high-frequency modulated signals. This intermediary transformation allows the power signal to be transmitted without directly interfering with voice communications, as the modulation process embeds the power signal within a carrier frequency that can be selectively filtered and extracted at the receiving end.
2Object-generated harmful factors
If DC power is transmitted over active telephone lines, then signal interference is reduced, but power capacity is limited to low power levels
Solution Approach 1:
The patent changes the parameter of DC power transmission by superimposing it with an AC carrier signal through frequency modulation. This transforms the transmission mode from direct DC to modulated AC, enabling higher power levels to be transmitted while maintaining the advantage of reduced interference. The power capacity is enhanced by utilizing the modulated signal's ability to carry higher energy without directly interfering with voice bands.
Solution Approach 2:
The patent creates a composite signal structure by combining DC power with an AC carrier wave through frequency modulation. This composite signal contains both the power delivery component (DC) and the transmission medium component (AC carrier), allowing the system to achieve high power capacity while maintaining signal integrity and minimizing interference through the separate frequency domains.
3Adaptability or versatility
If DC signal is imposed on telephone wiring, then independence from PBX/CO DC characteristics is achieved, but telephone off-hook detection functionality is lost
Solution Approach 1:
The patent segments the signal transmission by separating the DC power signal from the AC voice signal paths using AC Pass/DC Stop and DC Pass/AC Stop devices. This segmentation allows independent DC signal imposition on the wiring while preserving the AC voice signal path that carries off-hook detection tones to the PBX/CO, thus maintaining telephone functionality while achieving DC independence.
Solution Approach 2:
The patent introduces intermediary filtering devices (AC Pass/DC Stop and DC Pass/AC Stop) that mediate between the DC power signal and the AC voice signal. These intermediaries allow the DC signal to be imposed independently on the wiring while simultaneously passing AC signals unchanged to the PBX/CO, thereby preserving off-hook detection functionality while achieving DC signal independence.
Data Source
AI summary
A telephone unit device connectable in series between a telephone set and a wire pair coupled to a telephone service and carrying DC power and an AC telephone signal. The device includes: a first connector connectable to the wire pair; a second connector connectable to the telephone set; means connected between the first and second connectors for passing substantially without change the AC telephone signal between the wire pair and the telephone set; and means connected between the first and second connectors for receiving DC power only from the wire pair and converting the DC power to a level suitable for proper telephone operation of the telephone set connected thereto.