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eHam Forums => RFI / EMI => Topic started by: NG0Z on July 16, 2014, 09:04:53 AM



Title: RFI from neighbor's disconnected cable service box
Post by: NG0Z on July 16, 2014, 09:04:53 AM
With an MFJ-856 noise detector, I have pinpointed severe neighborhood broadband RFI to my neighbor's gray plastic Comcast cable box on the outside of his house. He is not a Comcast subscriber, so I am assuming it was disconnected improperly.

Any tips or advice on fixing this myself? Comcast is not very responsive and I can't imagine this is very complicated.

73

NG0Z


Title: RE: RFI from neighbor's disconnected cable service box
Post by: KF7CG on July 16, 2014, 09:35:32 AM
If a radio club in your area has an RFI comittee, get their help in talking to the neighbor. Don't do anything with the box as both Comcast, the neighbor, and autorities may take a dim view of that.

While your neighbor maynot use Comcast for TV, he may be using Comcast High Speed Internet. If he is totally off Comcast, you might want to help him find the power supply for the Comcast box and unplug it. If the Comcast box is plugged in it can of course cause you interference and as a selling point to him to help you, it is costing him money for electricity.

KF7CG


Title: RE: RFI from neighbor's disconnected cable service box
Post by: NG0Z on July 16, 2014, 09:38:00 AM
The neighbor is aware and cooperative. Good question on the high-speed internet. I will check. Thank you for the reply.


Title: RE: RFI from neighbor's disconnected cable service box
Post by: W5WSS on July 16, 2014, 11:15:07 AM
I think the noise is legitimate. It could be that the coaxial service line or more than one may be disconnected leaving the F series female connectors UN terminated and inherently causing RFI.

The Tech may not have had any terminators during a service call etc.

Getting them to come out and do it?

Who knows.

I debated this very issue with a ham whom employed as a Cable service tech adamantly strictly denied the possibility of RFI from UN terminated output connectors of their system there was never any closure to the debate.

73


Title: RE: RFI from neighbor's disconnected cable service box
Post by: NK7Z on July 16, 2014, 01:13:07 PM
With an MFJ-856 noise detector, I have pinpointed severe neighborhood broadband RFI to my neighbor's gray plastic Comcast cable box on the outside of his house. He is not a Comcast subscriber, so I am assuming it was disconnected improperly.

Any tips or advice on fixing this myself? Comcast is not very responsive and I can't imagine this is very complicated.

73

NG0Z
Just contact the local office of Comcast.  Ask to speak to a local RF engineer, (don't take no for an answer), and explain the problem to him/her.  If Comcast fails to correct the problem, (and I am betting they will correct it post haste), drop the word(s) "Incidental Radiator","cable leakage", and "RFI", into the discussion you are having with them.  

Remember, always be nice, always take notes, and always assume it will go South.  If Comcast does not respond, you have simple, speedy legal recourse, that is free via the FCC.  

Take notes!  Note who you spoke to, what you said, the time, the date, what they said, what happened, and what they said would happen...  If they become sticky go to: http://www.fcc.gov/guides/cable-signal-leakage (http://www.fcc.gov/guides/cable-signal-leakage) and ask Comcast to help you fill the form out.

Nine times out of ten things will go simple, you tell them, they fix it...  Only rarely do things go South, but it is YOUR JOB to be kind to them, and not to arrive being contentious...  You MUST treat them well at all times.  Else you loose the position of strength you have now.

I have a series of RFI location and fix articles up at: http://nk7z.net/rfi-now/ (http://nk7z.net/rfi-now/), the link to Part II, is within Part I.


Title: RE: RFI from neighbor's disconnected cable service box
Post by: NG0Z on July 16, 2014, 01:36:44 PM
Thanks Dave - very helpful

73 de NG0Z


Title: RE: RFI from neighbor's disconnected cable service box
Post by: NK7Z on July 16, 2014, 01:42:43 PM
Thanks Dave - very helpful

73 de NG0Z
Right now, you are in the drivers seat of this bus...  :)  A good place to be!


Title: RE: RFI from neighbor's disconnected cable service box
Post by: W1BR on July 17, 2014, 08:32:28 AM
I'm kind of surprised that an unterminated F connector can spray RF over a wide area, and such a wide frequency range.  I've seen unterminated RF fitting cause problems in lab environments when measurements are many dB down on spectrum analyzers, etc.

If this is broadband RF radiation across the HF spectrum, I'd be looking for a common mode radiation source... such as a length of 75 cable with a poor shield connection at the pole.

I'd suggest having the provider disconnect the cable at the pole drop to be safe.

Pete k1zjh


Title: RE: RFI from neighbor's disconnected cable service box
Post by: K1CJS on July 19, 2014, 07:11:09 AM
Comcast really doesn't care--and the FCC will side with them most of the time.  I remember a few years ago when Comcast had a leaky drop point near a VHF repeater.  The repeater was hanging because of the leaky signals out of the Comcast system--and it took an act of God to get them out there to fix it.


Title: RE: RFI from neighbor's disconnected cable service box
Post by: N0YXB on July 19, 2014, 09:14:59 AM
I'm kind of surprised that an unterminated F connector can spray RF over a wide area, and such a wide frequency range.  I've seen unterminated RF fitting cause problems in lab environments when measurements are many dB down on spectrum analyzers, etc.

If this is broadband RF radiation across the HF spectrum, I'd be looking for a common mode radiation source... such as a length of 75 cable with a poor shield connection at the pole.

I'd suggest having the provider disconnect the cable at the pole drop to be safe.

Pete k1zjh

I recently attended an excellent Rohde and Schwartz webinar and was surprised to learn CATV leakage from unterminated connectors and other cable faults are a common source of interference with 700 MHz LTE systems.  


Title: RE: RFI from neighbor's disconnected cable service box
Post by: AA4PB on July 19, 2014, 10:59:17 AM
Unused coax should have a 75 Ohm terminator on the end. Otherwise the mismatch at the end will cause a very high SWR on the cable and perhaps common mode radiation from the shield.


Title: RE: RFI from neighbor's disconnected cable service box
Post by: K0JEG on July 20, 2014, 11:04:41 AM
The response from Comcast could be to get someone right on it, or not to do anything, depending on what kind of mood the local folks are in that day. If the neighbor has a satellite system it could be that the installer used the in-house coax by just cutting off the line outside of the Comcast box. Depending on how sharp his diagonal cutters were it might have crushed the shield up against the center conductor. Or it could be as simple as tightening up the F connectors and terminators on the ground block.

Here's where it gets interesting. Since Comcast has eliminated their analog and clear QAM service, they have begun to implement "hot drop," meaning instead of physically disconnecting a drop from the hardline when a customer disconnects, they deauthorize equipment. However, since most of the noise and ingress problems come from house and drop wiring, they should be disconnecting and replacing bad drops. Depending on what the local system's priorities are it could go either way. The local office should be willing to respond, especially if you tell them you traced it down to a specific house. If not, you should fill out FCC form 2000E (https://esupport.fcc.gov/ccmsforms/form2000.action?form_type=2000E) with as much detail as possible.


Title: RE: RFI from neighbor's disconnected cable service box
Post by: W5WSS on July 23, 2014, 01:29:40 PM
PSST you did not hear this from me!

 IF? you do not get the issue resolved perhaps you can gain access to the exposed coaxial cables? Make a 75 ohm termination. Use an F-56 connector and o-ring and a 75 ohm resistor slide the resistor inside through the center connector crimp the resistor lead by sliding it underneath the o-ring and wedged to the connector body make sure the other resistor lead is long enough to press into the f series to a f series barrel splice screw both together.

I made millions of them for an MATV service company to terminate FDP 75 ohm tap offs at the end of a series of service outlets.

73

I know just saying.  But the termination is that easy to construct.


Title: RE: RFI from neighbor's disconnected cable service box
Post by: W8AAZ on July 23, 2014, 05:04:55 PM
Why not just put a short across the sunofagun!  That ought to maybe take care of it.  Maybe if it actually causes a problem, it would get someone out to deal with it, finally.


Title: RE: RFI from neighbor's disconnected cable service box
Post by: K1CJS on July 24, 2014, 06:11:12 AM
Terminating with a resistor across the center and the shield could still allow RFI.  Best to simply cap the end using a threaded F connector and a steel cap made for cable TV termination purposes.


Title: RE: RFI from neighbor's disconnected cable service box
Post by: KK5DR on July 26, 2014, 07:13:38 PM
Don't say I told you to do this, and I'll deny I posted it here. ( I'll say my account was hacked).
If you can seek over to the cable box armed with a hand full of F-type male 75 ohm TV cable terminators. You can put them on the end of each and every cable connector you can find in that box. That should reduce or eliminate your noise source.


Title: RE: RFI from neighbor's disconnected cable service box
Post by: K4PIH on August 07, 2014, 06:57:31 AM
I remember reading some time ago that leaky cable TV connections accounted for over 50% of RFI problems in the US. It was so bad that the FAA did random detection around airports and found that the leaky connections did cause issues with aircraft systems and terminal communications.

I lived in Vegas for a year and never had to subscribe to cable TV. The terminal box was in-grould on the line between me and the house next door. They suscribed and when the tech hooked them up, he left all the other connections unterminated. There was enough signal radiated and contained in the in-ground bos that my unconnected 75 ohm CATC acted like an antenna. Sure I didn't get all the channels, needed a converter box to get that, but I was able to get enough to watch.

In my area (Northern Virginia) the cable companies can;t keep up with the growth so the sub out the installs to any one with a ladder and a pair of pliers. We get some pretty bad interference from the cable drops.