Why is my cable line picking up FM radio? - AVS Forum
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post #1 of 12 Old 07-09-2012, 06:11 AM - Thread Starter
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My Comcast cable line coming in off the street is picking up FM radio stations very clearly. I live in an old home in the city of Pittsburgh, so there are several things here I think "could" be happening. Let me run down my setup.

Cable line from street-->APC UPS-->three way cable splitter-->

split 1) cable modem
split 2) cable card tuner
split 3) qam/atsc/fm tuner

I noticed a tiny spark and received a very small shock when I connected the line from the UPS to the splitter. The UPS is plugged (temporarily) into a two prong outlet with an adapter until I can replace the outlet when I'm on vacation next week. I'd like to test tonight if the FM still comes through without the UPS in the chain (I think I tried it and it did but I want to confirm).

I actually really like the fact I am getting the FM stations because it allows me to get both QAM stations and FM radio.

There are problems though. A few cable card channels are not coming in at all (or do very sporadically) and many of the clear qam ones are pixelated messes.

I am under the belief that QAM frequencies overlap to some extent with FM ones. Could the fact that the FM transmissions are getting into the cable line causing the problems with some channels? What is the more likely culprit - the FM getting in through the cable or though the electrical wiring?


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post #2 of 12 Old 07-09-2012, 07:51 AM
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Quote:
Originally Posted by pittsoccer33 View Post

My Comcast cable line coming in off the street is picking up FM radio stations very clearly. I live in an old home in the city of Pittsburgh, so there are several things here I think "could" be happening. Let me run down my setup.
Cable line from street-->APC UPS-->three way cable splitter-->
split 1) cable modem
split 2) cable card tuner
split 3) qam/atsc/fm tuner
I noticed a tiny spark and received a very small shock when I connected the line from the UPS to the splitter. The UPS is plugged (temporarily) into a two prong outlet with an adapter until I can replace the outlet when I'm on vacation next week. I'd like to test tonight if the FM still comes through without the UPS in the chain (I think I tried it and it did but I want to confirm).
I actually really like the fact I am getting the FM stations because it allows me to get both QAM stations and FM radio.
There are problems though. A few cable card channels are not coming in at all (or do very sporadically) and many of the clear qam ones are pixelated messes.
I am under the belief that QAM frequencies overlap to some extent with FM ones. Could the fact that the FM transmissions are getting into the cable line causing the problems with some channels? What is the more likely culprit - the FM getting in through the cable or though the electrical wiring?

This is called ingress and is a serious problem that needs to be corrected by a tech. Call Comcast and let them know as this IS service impactful.

~All truth goes through three phases. First, it is ridiculed. Second, it is violently opposed. Third, it is accepted as self-evident. - Arthur Schopenhauer ~
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post #3 of 12 Old 07-09-2012, 09:34 AM
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Why do you suspect FM as the problem? FM is broadcasted between channels 6 and 7.
Who installed the 3 way spliiter and coax runs in your home.... you or the cableco?
Have you tried temporarily running a direct feed from the incoming line to one of the problematic tuners to see if the reception is better?

Maybe you just have poor/low signal. Be aware that if the cableco did not install the wiring in the home or the 3-way spitter, they will only test the incoming feed. Any additional "testing" of DIY stuf inside the home will incur a service charge.
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post #4 of 12 Old 07-09-2012, 11:09 AM - Thread Starter
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Quote:
Originally Posted by BHNtechXpert View Post

This is called ingress and is a serious problem that needs to be corrected by a tech. Call Comcast and let them know as this IS service impactful.

Serious as in screws with your service, screws with other customer's service, or as in damages equipment?

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Why do you suspect FM as the problem? FM is broadcasted between channels 6 and 7.
Who installed the 3 way spliiter and coax runs in your home.... you or the cableco?
Have you tried temporarily running a direct feed from the incoming line to one of the problematic tuners to see if the reception is better?
Maybe you just have poor/low signal. Be aware that if the cableco did not install the wiring in the home or the 3-way spitter, they will only test the incoming feed. Any additional "testing" of DIY stuf inside the home will incur a service charge.

-I remember reading way back that FM frequencies overlapped to some degree with QAM ones, but I can't find where I read that. So it was just an idea I had in my head since the FM is not supposed to be there.

-They installed the line, I installed the splitter. The line comes in right through the wall from the street. Running direct to to the cable card tuner doesn't help with the missing channels.

-I do think I have a poor quality signal, given read outs by my cable card tuner. I didn't know if the radio interference could be the culprit.

I'm off for a while at the end of the month so I'll probably have to wait until then until I'm able to have a person come out. I appreciate the feedback.


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post #5 of 12 Old 07-09-2012, 03:37 PM
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FM overlaps cable channels 95 (90-96 MHz), 96 (96-102 MHz) and and 97 (102-108 MHz). Cable companies generally either skip these channels or put low priority programming on them, like shopping or religious channels. In most markets where I do business, there are also strong, interfering signals on channels 19 and 20, so cable companies often put low interest programming on those channels as well
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post #6 of 12 Old 07-09-2012, 09:06 PM
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What kind of CableCard Tuner do you use? If it's the HDHR Prime, you can run the Diagnostic GUI and see what TV Networks are on channel 95, 96 & 97. That way you can check if the FM is causing a problem. While on that page you can also look at signal level and quality.
374

If it's a Ceton or Hauppauge, there's probably a similar diagnostic available.


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post #7 of 12 Old 07-10-2012, 07:54 AM
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"Serious as in screws with your service, screws with other customer's service, or as in damages equipment?"

Cable systems are designed to be a closed system no ingress or egress. This ingress that you are seeing is most likely causing many problems in your neigborhood "NODE". Ingress or noise will cause data loss or corruption resulting in slow data speeds, intermittent modem connections, VOIP problems such a jitter and echo, and digital video problems such as pixalation and black screens.
These problems are caused by damaged cables ffrom such things as animal chews, cracked cables from storm damage. But the majority of issues are caused by poor conectors and cable that doesn't meet the shielding characteristics required by a HFC network ie. 75 Ohms of impedence. This is most often a result of DYI using materials designed for an OTA antenna install.
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post #8 of 12 Old 07-10-2012, 09:35 AM
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Cable companies are regularly cited and fined for egress problems due to damaged cables and equipment. Their cables are transmitting RF on a wide range of frequencies from everywhere their cables go. If these signals leak, they can cause local interference with wireless services like police and fire. This can be a more serious problem than a cable customer having reception problems.

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post #9 of 12 Old 07-10-2012, 10:06 AM
 
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Quote:
cable that doesn't meet the shielding characteristics required by a HFC network ie. 75 Ohms of impedence.

Characteristic impedance isn't the same as an electrostatic shield.
Quote:
This is most often a result of DYI using materials designed for an OTA antenna install.

Why do you think there is a difference between the frequencies used for OTA and cable? The cables are the same.
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post #10 of 12 Old 07-10-2012, 10:49 AM
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Rather than everyone competeing and throwing out "knowledge", why not contact to the cableco to remediate?
It is possible that the cableco provides "local" FM, wink.gif
The poor "TV" signals could be attributed to another issue.

If egress were an issue... that would be reported.
If ingress is the only issue, then you have a powerful FM x-mitter very close and you have bad cables/connectors.
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post #11 of 12 Old 07-10-2012, 11:52 AM - Thread Starter
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Originally Posted by Ratman View Post

Rather than everyone competeing and throwing out "knowledge", why not contact to the cableco to remediate?

The three reasons I haven't are

1) I live alone and just don't have the time to wait for them, and

2) I don't want to be charged $80 for the guy to tell me electrical interference from an old outlet is causing it and he is washing his hands of that.

3) The only channel I miss that I remotely care about is History, but even that is mostly reality junk now. H2 is where its at cool.gif

I am going to try trouble shooting a few things this weekend. I'll be off for a few weeks at the end of the month and will get it solved once and for all then. I appreciate all the different feed back though, it's been pretty interesting reading about RF leak and whatnot the last two days.


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post #12 of 12 Old 07-10-2012, 02:28 PM
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When you have time off, have them come out..
You pay for a "service". They will check levels and service from pole/ped to your demarc without cost.

True.... if he says all is good, it's up to you to get all of the cable runs, connectors, splitters and whatever "up to snuff" within your premises.
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