Cable Splitter

[A/A Fuel GTX]

Is it necessary to cap off unused ports on a cable splitter?

 

[LarryFine]

I deally, they should be terminated with 75 ohm resistors, which terminator caps have soldered in them, to minimize image ghosting.

However, the signal loss is still there. It's best to use a splitter with the number of ports you have supplying tuners, and no extras.

 

[hbiss]

The term is not "cap off" it's terminate. Terminators for CATV have 75 ohm resistors in them. The answer to your question is yes, all unused ports need to be terminated. Not only that, all unused jacks need a terminator also.

-Hal

 

[curt swartz]

Back in the antenna days I would frequently see terminators on unused ports but I have never seen a CATV provider install one.

 

[480sparky]

Just about every electonics store sells 75ohm terminations.

 

[A/A Fuel GTX]

OK, so with CATV or Satellite, what is the result if the ports are not terminated?

 

[jumper]

It has to do with a phenomena called reflective wave. When the cable is not terminated or terminated with a load that is unequal to the cables impedence, part of the signal (power) is reflected back to the source and causes problems.

You can read more about it here

http://www.allaboutcircuits.com/vol_2/chpt_14/4.html

What is interesting is that TDR technology uses reflected waves to find shorts, opens, and distances in cables.

 

[shepelec]

You also need to keep in mind, CATV is an RF product. So by using cheap "Walmart" cable or improper terminations you can cause signal degragation, bleed over and allow outside RF signals into the system.

This is how CB and HAM radio interfere with CATV quality.

 

[K8MHZ]

You also need to keep in mind, CATV is an RF product. So by using cheap "Walmart" cable or improper terminations you can cause signal degragation, bleed over and allow outside RF signals into the system.

This is how CB and HAM radio interfere with CATV quality.

Yeah, but it's the responsibility of the CATV accept all interference.

It is also the responsibility of the CATV device in question NOT to interfere with amateur radio. I know, I have worked with our cable company to locate the source of RFI coming from a cheap amp someone installed in their home. The FCC will fine people for not making the required corrections if they are interfering with radio communications. They even fine power companies for having arcing insulators that interfere with amateur radio communications.

 

[shepelec]

Yeah, but it's the responsibility of the CATV accept all interference.

It is also the responsibility of the CATV device in question NOT to interfere with amateur radio. I know, I have worked with our cable company to locate the source of RFI coming from a cheap amp someone installed in their home. The FCC will fine people for not making the required corrections if they are interfering with radio communications. They even fine power companies for having arcing insulators that interfere with amateur radio communications.

Maybe I like listening to the soap opera audio in the 150Mhz band.:grin:

 

[hbiss]

Yeah, but it's the responsibility of the CATV accept all interference.

Not sure what you meant by that but I'll assume you have the right idea. Per the FCC cable systems are responsible for all leakage from their system and that includes that coming from within your or your customer's house where you did your handi-work. It's not so much to protect amateur radio, the concern is to protect critical and essential services like
aeronautical and emergency frequencies that operate over the air on the same frequencies the cable companies use that are supposed to be "sealed" within their cables.

Another concern is the opposite of leakage which is ingress. Ingress is where external over the air signals get into the cable system. Where there is leakage there will always be ingress through the same "hole" so they kind of go hand in hand. The most serious consequence of ingress is the disruption of entire areas of subscribers. Because the cable system is 2-way, signals go both downstream to the subscribers and upstream from the subscribers equipment back to the head end. A foreign signal in the return can degrade internet speed and the operation of set top boxes to completely shutting down an entire area if the return optical transmitter that converts the coax to fiber is overloaded with a high signal level.

Cable company people are always looking for leakage. Most have trucks with detector systems installed that report back to the office as the trucks go about their daily travels. When a problem is isolated to a building or house a tech will be dispatched to visit the premises to correct the problem. If admittance is not granted the service will be disconnected at the pole or pedestal until such time that it can be corrected.

-Hal