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Author Topic: Cable causing 2 meter intyerference?  (Read 4810 times)
N6HBJ
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« on: December 08, 2012, 07:10:07 PM »

I have Cable TV/Internet

Lately I have a bunch of dead carriers all over the two meter band and my internet is super slow. Could this be a cable internet problem/leak causing both issues?

Mike
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WX7G
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« Reply #1 on: December 09, 2012, 12:49:13 PM »

Disconnect the cable where it enters the house. Shut off the router.
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K0JEG
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« Reply #2 on: December 09, 2012, 12:53:25 PM »

Cable ch 18 is centered at 147MHz. If your cable company is using ch 18 for an analog signal you should see a video carrier at 145.25Mhz and hear a wideband FM audio carrier at 149.75. However, many cable companies have been converting their analog video channels to digital in order to offer more services using MPEG 2 compression. In that case ch 18 may be a QAM carrier, which uses a mix of phase and amplitude to send a datastream to a receiver that can demodulate and decode the signal into digital data (and ultimately a picture). These signals resemble wideband white noise due to their nature (they are sometimes referred to as a "haystack" because of how they look on a spectrum analyzer). QAM signals shouldn't necessarily produce a discernible signal on an analog receiver, just an increase in white noise.

If you are able to see or hear an FM carrier, it would indicate that there's a leak in the cable nearby. It might be in your house, it might be on the street, or even in your neighbors' house. If you're able to pick it up it's likely close by, because even with an ideal radiator it's only a few dB of signal output, and most leaks are far from ideal (although I've had a few that traveled for blocks when the lashing wire on overhead lines touched the center conductor on a cracked hardline).

If signal can get out, noise can get in, so it could be possible that your modem might be suffering from ingress. I doubt they use ch 18 for the cablemodem downstream carrier, basically because we know there's ham radio and other land mobile stations in that part of the spectrum (along with some other reasons not relevant). Usually you can check your modem settings by opening a web browser and going to http://192.168.100.1/ and checking for a "signal" or "status" page that should tell you what frequency is in use for both upstream and downstream, along with a signal quality measure called MER (should be better than 30dB for error free communication). But ingress is usually very broadband in nature and because of the proximity of powerlines and transformers it doesn't take much to trash the cable signal. So if you are seeing problems with your modem it woudn't hurt to call and see if someone can come out and check to make sure things are OK. Don't try to explain leaks or ingress to the folks at the call center, they most likely won't understand, but feel free to discuss with the tech who comes out to investigate. They should have leakage detection equipment on their truck that can help narrow down any problems.

Good luck.
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WX7G
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« Reply #3 on: December 10, 2012, 05:10:14 AM »

Are we getting ahead of ourselves here? It first must be determined if the cable is the source of noise.
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K0JEG
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« Reply #4 on: December 10, 2012, 06:10:39 AM »

Are we getting ahead of ourselves here? It first must be determined if the cable is the source of noise.

Well, if he has a general coverage receiver and can tune it to 149.75MHz he has a good chance of hearing ch18's sound. That would tell him there's a leak in the area. Depending on where that leak is, it might be huge or might be minor. Most HTs will tune outside the ham bands these days, so it wouldn't be very hard to check.

Maybe I did jump the gun, but if you're not getting the level of service you're paying for, call the company and get a service call scheduled. There's no excuse for slow speeds from your ISP these days, Internet service is a mature industry (I've been doing this since the mid 1990s, nearly 20 years {wow that makes me feel old!}) and there's a ton of lessons learned and knowledge built up over the years.
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N6HBJ
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« Reply #5 on: December 10, 2012, 11:55:22 PM »

K0JEG
You're a pretty cool dude. I asked a simple question. If it was possible that cable could be causing the interference based on my slow internet and new development of carriers over the 2 meter band. And you answered basically that it was and in great detail.
As a matter of fact I have a carrier at 145.251 as well as multiple other places. You haven't "jumped" any gun, but merely gave some possibilities to determine whether one cable channel was the culprit. Thank you. BTW I live in a condo - 1200 units. So disconnecting the cable from all the neighbors is not a possibility. Anyway, you answered my question - yes - and I'm having the cable tech come out tomorrow to fix my slow internet and hopefully determine if they have a leak. Not sure what the other guy's problem is. He doesn't seem very happy.
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WX7G
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« Reply #6 on: December 11, 2012, 05:00:08 AM »

N6HBJ, we are both trying to offer you sound technical assistance. Please don't comment on us personally, it serves no useful purpose.

 WX7G, NARTE Certified EMC Engineer
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WX7G
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« Reply #7 on: December 11, 2012, 03:34:54 PM »

Here's how I view troubleshooting the "dead carrier" issue:


If it's merely a curiosity and doesn't bother communication no work is needed.

If it bothers communication your solution is confined to the walls of your apartment.

Power the radio from a battery and shut off all of the AC circuit breakers to your apartment.

Disconnect the TV cable.

If the carriers are still there you are finished. There is nothing you can do.

If the carries are gone start isolating them to the source. Reconnect the cable TV cable and test. Switch ON the circuit breakers room by room and test.

Note that knowledge about any potential noise source is not part of this troubleshooting procedure.
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K1CJS
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« Reply #8 on: December 12, 2012, 05:23:17 AM »

It's extremely possible that the cable company equipment could be causing interference.  All it takes is a loose connection or an open port on a cable access point.  I remember one incident where the cable company leakage kept a ham repeater keyed up.  The input was 144.55, a little away from a carrier frequency of one cable channel.  Turns out that a bad leak at a connection block was the problem--but what a job to get the cable company to fix it!
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K1CJS
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« Reply #9 on: December 19, 2012, 04:42:37 AM »

Another point--once the cable feed comes into any apartment, if the person who connects up the TV set and anything else that hooks into that cable feed isn't too knowledgeable, they may use the cable that comes with the VCR or other item to connect it.  Most of those cables aren't 100 percent shielded like the cable that the cable company or builder installs.  They have a shield that has gaps in it--and that unshielded cable leaks the signal like a fire hydrant spews water when opened.

Even the cables supplied with the self install kits that some cable companies put out aren't fully shielded.  The white co-ax that comes with Comcast install kits is a good example.  I too had a similar problem--which all but disappeared when I changed out all those junky cables with quality RG6 and new F connectors.
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W5LZ
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« Reply #10 on: December 23, 2012, 08:20:34 PM »

Could your cable TV be causing interference on 2 meters?  Yes, it certainly can.  It used to be VERY common here, you could listen to HBO almost anywhere in town on your 2 meter radio.  It's better now.  It deals with the cable company's system, how they do the installations and maintain their lines.  I'm sure your company isn't as 'bad' as ours was... maybe.
As suggested, you want to make sure the cable company is at fault before telling them about their interference problem.  They get a lot of that sort of thingy and tend to ignore it unless you really make a PITA out of yourself.  Smiley
 - Paul
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KF7CG
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« Reply #11 on: January 07, 2013, 10:32:00 AM »

The HD revolution on the air eliminated some of the cable companies reason to chase leaks. Back in the analog days a cable ready tv and a fair antenna would net a homeowner all the cable channels for free.

Just point antenna at a leak and enjoy. You are not making an illegal connection just enjoying off the air reception.

KF7CG
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