RF leak detector

• US 4,072,899 A
• Filed: 04/26/1976
• Issued: 02/07/1978
• Est. Priority Date: 04/26/1976
• Status: Expired due to Term

• Current Assignee: ComSonics, Inc.
• Original Assignee: ComSonics, Inc.
• Inventors: Shimp, Richard L.
• Primary Examiner(s): Griffin, Robert L.
• Assistant Examiner(s): Bookbinder, Marc E.
• Application Number:
  US05/680,412
• Time in Patent Office: 652 Days
• Field of Search: 325/67, 325/363, 325/31, 325/308, 325/64, 325/131, 325/466, 178/DIG. 4, 178/DIG. 13, 179/175.3 F, 324/52, 324/67, 324/72, 324/95, 324/51, 324/66, 324/72.5, 340/384 E
• US Class Current: 725/143
• CPC Class Codes: G01R 31/083 in cables, e.g. underground
• CPC Class Codes: G01R 31/1272 of cable, line or wire insulation, e.g. using partial discharge measurements locating faults in cables G01R31/083
• CPC Class Codes: H04B 3/46 Monitoring; Testing
• CPC Class Codes: H04N 7/102 Circuits therefor, e.g. noise reducers, equalisers, amplifiers H04N7/108 takes precedence

Abstract

The detector is primarily useful in detecting RF leaks due to defects in the shielding in a CATV coaxial cable distribution network. RF leaks are detected by transmitting a unique signal and using a very narrow band receiver to detect the unique signal to thereby detect small amounts of RF leakage from the CATV coaxial cable distribution network at the locations of defects in the shielding. The leakage from the CATV coaxial cable distribution network is due to defects in the shielding such as small cracks in the cable, loose fittings or other non-RF tight conditions. The detector is a three-part system including a transmitter, a remote cable powered preamp and antenna assembly, and a narrow band receiver providing an audio output. The transmitter is designed to be permanently installed at the head end location and is modulated with a unique audio tone. An RF leak is detected by moving the remote preamp and antenna assembly along the coaxial cable distribution network of the CATV system. When the remote preamp and antenna assembly picks up leakage RF energy, the unique audio tone will be detected, and the detected audio signal fed to a loud speaker or earphones. The audio tone is readily recognized by the operator.

Claims

1. A method of detecting RF leaks due to defects in the shielding of a coaxial RF communications medium comprising the steps of:

applying an RF signal, which is modulated by a unique signal, to the coaxial RF communications medium, and

detecting said unique signal with a narrow band receiver and antenna to thereby detect small amounts of RF leakage from the coaxial RF communications medium at the locations of defects in the shielding.

2. A method as recited in claim 1, wherein said unique signal is a warbling audio tone and said step of detecting includes the further step of aurally reproducing said warbling audio tone.

3. A system for detecting RF leaks due to defects in the shielding of a coaxial RF communications medium comprising:

means for applying an RF signal, which is modulated by a unique signal, to the coaxial RF communications medium,

movable antenna means for receiving any RF leakage from the coaxial RF communications system, and

receiver means connected to said movable antenna means for detecting said unique signal to thereby detect small amounts of RF leakage from the coaxial RF communications medium at the locations of defects in the RF shielding.

4. A system as recited in claim 3, wherein said unique signal is a warbling audio tone and said receiver means includes

a detector for detecting said warbling audio tone modulation on the received RF leakage, and

audio means connected to the output of said detector for aurally reproducing the detected warbling audio tone.

5. A system as recited in claim 4 wherein said receiver means further includes

a narrow bandpass IF amplifier and filter connected between said movable antenna means and said detector, and

Agc means connected to the output of said detector for controlling the gain of said IF amplifier, said AGC means being adjustable to vary the dynamic range of said receiver means.

6. An RF leak detector for CATV systems of the type having a transmitter located at a head end and a coaxial cable distribution network emanating from said head end to a plurality of subscriber'"'"'s terminals, said detector comprising:

means located at said head end for generating an RF signal which is modulated by a unique signal,

means for coupling the modulated RF signal to said distribution network,

antenna means adapted to be moved proximate to the coaxial cable distribution network for receiving any RF leakage due to defects in the shielding of the coaxial cable distribution network, and

receiver means connected to said antenna means for detecting said unique signal to thereby detect small amounts of RF leakage from the coaxial cable distribution network at locations of defects in the shielding of the coaxial cable distribution network.

7. A detector as recited in claim 6 wherein said unique signal is a warbling audio tone and said receiver means includes

a detector for detecting said warbling audio tone modulation on the received RF leakage from the sheathed cable, and

audio means connected to the output of said detector for aurally reproducing the detected warbling tone.

8. A detector as recited in claim 7 wherein said audio means is adjustable to vary the volume of the reproduced warbling audio tone and said receiver means further includes

a narrow bandpass IF amplifier and filter connected between said movable antenna means and said detector, and

Agc means connected to the output of said detector for controlling the gain of said IF amplifier, said AGC means being adjustable to vary the dynamic range of said receiver means.

9. A detector as recited in claim 8 wherein said audio means includes earphones to be worn by an operator.

10. A method of detecting RF leaks due to defects in the shielding of coaxial cables of CATV systems of the type having a transmitter located at a head end and a coaxial cable distribution network emanating from said head end to subscribers'"'"' terminals, said method comprising the steps of

generating an RF signal which is modulated by a unique warbling audio tone at the head end,

coupling the modulated RF signal into said coaxial cable distribution network,

moving an antenna along the coaxial cable distribution network to receive any leakage RF energy from the coaxial cable distribution network,

detecting said unique warbling audio tone to thereby detect small amounts of RF leakage from the coaxial cable distribution network at the locations of defects in the shielding of the coaxial cable distribution network.

11. In an RF leak detecting system for locating RF leakage due to defects in the shielding of coaxial cables in CATV systems of the type having a transmitter located at a head end and a coaxial cable distribution network emanating from said head end to a plurality of subscribers'"'"' terminals, said RF leak detecting system including an antenna adapted to be moved proximate to coaxial cable distribution network for receiving any RF leakage from the coaxial cable, distribution network, and a receiver connected to said antenna, the improvement comprising:

means located at said head end for generating an RF signal which is modulated by a unique audio signal, and

means for coupling the modulated RF signal to said coaxial cable distribution network, said receiver being tuned to said RF signal and capable of detecting and aurally producing said unique audio signal at the locations of defects in the shielding of the coaxial cable distribution network.

12. A device for use with a movable antanna for receiving RF leakage due to defects in the shielding of a coaxial RF communications medium and a receiver connected to said movable antanna, said device comprising:

means for generating an RF signal which is modulated by a unique signal, and

means for coupling the modulated RF signal to the coaxial RF communications medium, said receiver being tuned to said RF signal and capable of detecting said unique signal at the locations of defects in the shielding of the coaxial RF communications medium.