How to identify CATV leakage causing RF interference
Cable Television (CATV) operates over a wide range of frequencies. Typically this encompasses the frequencies classified as VHF Low (54 MHz) up to the middle of UHF (800 MHz). Additionally CATV companies may use 7MHz – 49 MHz for “return” or “reverse” services. Since CATV is designed as a physically closed or shielded network, interference is normally of no concern for over-the-air signals such as those listened to by scanner or SWL enthusiasts. However if any part of the network (from the Head End all the way to the back of your TV set) is compromised, you can have what is referred to as “signal leakage”. Signal leakage, depending on its severity, can cause interference to a wide range of users, including but not limited to Aeronautics, Public Safety, Amateur Radio Operators and scanner and SWL listeners. This is because when a leak occurs, all frequencies in use by the CATV operator to distribute their signal can “leak” out, acting like a mini broadband transmitter. In extreme cases, some leaks may even interfere with Aircraft communications and/or navigation (108-136MHz and 225-400MHz). This is the area of highest concern to the FCC (47 C.F.R. §§ 76.611 - 76.617)
The FAQ below is intended to assist you in identifying possible CATV leaks causing interference to your radio reception, but may not be all-inclusive. Interference to your radio reception may be caused by any number of factors other than CATV.
Do not tamper with connections not physically attached to your residence (if in a single-family home) or any connections except those attached directly to your CATV box, video player or TV (if in a multi-unit dwelling). Above all, USE COMMON SENSE.
• How can I tell if CATV signal leakage is possibly causing interference?
Does your scanner seems to stop on frequencies with a “dead carrier”, other than known “birdie frequencies” in a particular location?
Can you can hear a distinct buzzing noise (video carrier) accompanying the audio when a known frequency is in use?
• How do I know where the leakage is coming from?
Using a handheld scanner, search the area between 108 and 136 MHz in AM mode for a warbling sound (common frequencies to check are 108.0054, 109.275, 114.0057, 115.275, 120.0060, 121.2625, 126.0063, 127.2625, 132.0066 and 133.2625). If you find this sound, it will most likely be the CATV provider’s injected audio signal used by their personnel to identify signal leaks. It can only be heard if a signal leak is present.
To identify if the leak is coming from inside your home, move towards each connection point with your handheld scanner and see if the signal and sound grow in intensity. If you seem to get the same levels from each connection around the house, try disconnecting all and reconnecting one line at a time to “survey” them individually. Remember not to let the center conductor of any active CATV cable touch any metal once you’ve disconnected it or it will become a radiator and a signal leak itself.
Check all coaxial CATV connectors to make sure they are “finger-tight” and not damaged. While most CATV connectors are hex-type to accept a standard SAE open-end wrench, I would advise against this as it wouldn’t take much force to over-tighten it and break the chassis connector it’s attached to.
Check to make sure the jacket on any of the cables hasn’t been broken by pinches or animal chewing. Check to see if you have any “cheap” jumpers in use that are smaller in diameter (less shielding) than those cables provided by your CATV company.
Are you using anything other than coaxial cable to pass the CATV signal from one room to the next or component to component? (I once found a customer using speaker cable for this purpose)
Do the CATV cables have connectors on them where they pass through non-living areas of the house, i.e. – attics, crawlspaces, laundry rooms, etc.? If so, you may need to check them if you’ve already eliminated all other connections inside the house.
Check your outside connections on the house (if you live in a multi-unit dwelling, contact your CATV provider) and make sure the connections are tight and un-damaged. Also check to make sure that any splitters do not have cracked housings.
Lastly, how is the cable attached to the outside of the structure? If staples have been used, you’ll have to check each one to insure none have perforated the cable’s jacket. If one has, contact your CATV operator to repair it.
Check to see if your drop cable (connection to the CATV system) is exposed (if buried) and if so, is there any damage to the jacket? If so, report it to your CATV provider.
If none of these steps resolve the issue, there may be a leak outside of your domicile and you should contact your local CATV provider.
• Who should I report suspected signal leaks to?
Your local CATV operator is responsible for all signal leaks emanating from their system or a subscriber connected to it, per FCC regulations.
• Does the CATV operator have to fix every leak?
Per the FCC: “During regular monitoring, any leakage source which
produces a field strength of 20 uV/m or greater at a distance of 3 meters in the aeronautical radio frequency bands shall be noted and such leakage sources shall be repaired within a reasonable period of time.”
If the CATV operator determines that the leak is caused by subscriber supplied equipment, they may ask you to replace it or have them replace it at your cost. This is usually at the discretion of the Service Person present and depends on what the piece is that is causing the leak. Be aware that TVs and other components themselves have been known to cause leaks on rare occasions.
If the CATV operator cannot access a residence where a leak has been determined to originate from, they may disconnect that residence from their network until the leak can be eliminated.