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Old 02-07-2018, 10:29 PM
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Default Cable TV Interference Issue

Group,

I am getting severe interference with my cable tv box and/or television from my own two way radio transmissions. I have a radio in the house at the other end of the house, the antenna is on the roof of the house, and I also have a radio in my car that is in the garage downstairs below the tv being affected. Frequencies used range from 144 MHz to 450 MHz, tx power ranges from 2 watts to 45 watts. I have done everything that I can think of to get it to stop, but no luck. I can only assume poor filtering or shielding in the cable tv box or tv itself. When transmitting the picture on the tv breaks up so bad it distorts the picture and if transmitting for more than about 3 to 5 seconds the picture completely disappears and the screen goes black, once the transmitter shuts off about 10 seconds later the picture shows up on the tv screen. I am unsure HOW the RF signal from my radios are getting into the Cable TV Box and/or Television and am out of ideas for a solution to isolate them from each other. Anyone else have this problem, any suggestions?

P.S. Probably don't help but attached photos show the Cable TV Boxes I am using.

Thank you,
Doug
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Last edited by dapaq2; 02-07-2018 at 11:02 PM..
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Old 02-07-2018, 10:46 PM
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Crap leaks out of the cable TV system and these boxes, so in the presence of high RF fields, it makes sense that your transmitter is getting in.

The behavior of your TV sounds exactly like what happens when my off the air TV antenna loses enough signal.

You could call the cable TV company, but you could also drive rusty wood screws up under your finger nails. Each one would be about equally pleasant and have the same general outcome. The Cable TV company should be able to come out and diagnose this, but the random tech you get usually isn't very good at it.

Before you pick one of the two above optionsů
Make sure you are using decent coaxial jumpers on all your TV equipment. Make sure all connectors are tight and properly installed. Make sure unused ports on splitters, etc. are terminated.

Do the same with your radios. You didn't tell us what frequencies you are using, though. Make sure your SWR is low. Make sure it's good coax, connectors properly installed.

General rule of thumb is to start isolating parts of your system to see if there is a specific cable, TV, or part of the house that is more impacted. Work from there and look for issues.
Also, try turning down your TX power. Make sure antennas and radio coax is well separated from your cable TV gear. Make sure everything is properly grounded, that means the amateur stuff and the cable TV stuff.

But I suspect what you will find is that it's just getting in through various paths, as in more than one. Even through the plastic case of the modem/router. Playing with some torrids/ferrites might be a good place to start. Try on the cable TV box power line, Ethernet cords, USB, etc. Anything that connects to the box.

Don't rule out the idea that the issue is outside your house. Talk to your neighbors and see if they experience the same thing when you transmit. Bad connectors, unterminated outputs, left over drop lines, etc. are all places where RF can get in.

Good luck, I think you are going to need it.
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Old 02-08-2018, 6:35 AM
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Are there any places where the radio coax runs alongside your TV coax? Where is the outdoor antenna in relation to your TV coax and equipment? How high is it?

Transmitting with the mobile while the car is parked in the garage is a bad idea for many reasons. Don't.
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Old 02-08-2018, 6:56 AM
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Quote:
Originally Posted by dapaq2 View Post
Group,

I am getting severe interference with my cable tv box and/or television from my own two way radio transmissions. I have a radio in the house at the other end of the house, the antenna is on the roof of the house, and I also have a radio in my car that is in the garage downstairs below the tv being affected. Frequencies used range from 144 MHz to 450 MHz, tx power ranges from 2 watts to 45 watts. I have done everything that I can think of to get it to stop, but no luck. ...
Doug
Have you put toroid chokes around the outside of the TV and cable TV cable boxes and done similar to their power? The chokes should be placed on the cables and power wires near the devices. Also, make sure there are no pieces of lose metal touching other lose metal near your antenna and all grounding is in proper shape.
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Old 02-08-2018, 8:05 AM
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Are there any places where the radio coax runs alongside your TV coax?
No, close as it gets to the cable tv coaxial cable is about 25 feet, and does not run parallel to it at any point in its run.

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Originally Posted by jonwienke View Post
Where is the outdoor antenna in relation to your TV coax and equipment?
On the roof, about 30 feet opposite end of the house.

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Originally Posted by jonwienke View Post
How high is it?
About 24 to 26 feet off the ground.
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Old 02-08-2018, 8:09 AM
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Quote:
Originally Posted by dlwtrunked View Post
Have you put toroid chokes around the outside of the TV and cable TV cable boxes and done similar to their power?
Already tried that, made no difference or improvement.

Quote:
Originally Posted by dlwtrunked View Post
The chokes should be placed on the cables and power wires near the devices.
Already tried that, made no difference or improvement.

Quote:
Originally Posted by dlwtrunked View Post
Also, make sure there are no pieces of lose metal touching other lose metal near your antenna and all grounding is in proper shape.
There is no loose metal anywhere near the antenna.
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Old 02-08-2018, 8:58 AM
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Since you are experiencing trouble with the transmitters so far away from the cable box, I'd suspect a cable problem and one that isn't necessarily right at the cable box. It could be the point of entry into the house or anywhere in between. It could even be a poor quality length of cable or a problem before it enters the house.

I'd check for poor or loose connectors, unterminated splitter ports, maybe even replacing the splitters if they're old. Don't use the crappy coax jumpers that come with TVs and such. They're often RG59 coax or use push on connectors. I've had to replace some of the lengths of cable that were used when my house was built (now 40 years ago) because they have deteriorated. Lastly, you could temporarily disconnect Individual runs in the house (if you have multiple runs to different rooms) to try to isolate the problem. If it goes away, add those runs in one at a time and try to figure out the problematic lengths. Good luck. It sounds like you have your work cut out for you.
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Old 02-08-2018, 11:23 AM
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Do you have a handheld dual-band (2M and 70cm) transceiver / HT? (If not you can get one for less than $30 just to use as a test transmitter.) Turn the RF output power down to 1 watt (Low) or less and set it to whatever 2M or 70cm frequency was interfering the most from your mobile or base radio. You're going to use the HT as a source of RF to be injected to the TV cable system. First test is obvious: When you key the HT set to low power, does it get into the TV system? If not, GOOD. If it still gets in at low power, move around with the HT until you find a spot where when you transmit the TV(s) are not affected. Now go to various locations both near the CATV devices and farther away from them and key up the HT, noting the level of interference produced.... and where it is the worst. (You're probably going to need help from another person who is watching the TV and communicating with you. Do you have cordless phones in the house? Use their "Intercom" function to talk to each other.) When you find the spot(s) that produce the worst level of interference you will be close to the device(s) or cable(s) or connector(s) that are being affected.... and as noted in this thread, they may be outside or at the point of entrance to the house, on the pole, or at a CATV service box near your house.
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Old 02-08-2018, 12:42 PM
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As already mentioned Cable can use the same frequencies as we do as Amateurs. In theory the cable signal is supposed to stay on the inside of the cable system and the ham signals are outside. The issue is that the 'wall' leaks. As the problem is happening with you mobile as well as your home station, I wold start by asking my cable provider to disconnect any cable outlet in my home that is not in use. Then either you or the cable tech should check all connections and cables (loose connections, bad shield poor shield contact). If you tune around with your radio and just watch the received signal strength, you may notice high 'S' readings but you hear nothing and squelch never 'opens' Theses are likely cable TV signals leaking out. Good grounding can also help.

What is happening is that your signal is 'swamping' the receiver of the cable box. After you stop transmitting, the box has to require the signal, reset its timing and start decoding again. You may be affecting the TV of your neighbors as well.

I would call the cable company, and explain what is going on-they may already be getting calls and trying to find the problem-if so you can work on it together. Remember it is both or your jobs to resolve
the issue. Interference like this can indeed be challenging to resolve.

Good luck and 73
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Old 02-08-2018, 12:47 PM
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Quote:
Originally Posted by mmckenna View Post
Crap leaks out of the cable TV system and these boxes, so in the presence of high RF fields, it makes sense that your transmitter is getting in. ...splitters, etc. are terminated. ...

...Don't rule out the idea that the issue is outside your house. Talk to your neighbors and see if they experience the same thing when you transmit. Bad connectors, unterminated outputs, left over drop lines, etc. are all places where RF can get in.

Good luck, I think you are going to need it.
Many years ago, cable TV interference (strong) was leaking from the cable running *straight* across the power pole immediately behind our home, causing problems to our TV and my scanners. To make a long story short, there was no thermal contraction/expansion and wind stress cable section near the pole as shown in the first diagram here. (The "stretched" out u shaped section).

The problem was solved when the cable company installed a patch right at the pole. Cable TV interference was widespread throughout my area -- as I was able to detect it by using a handheld scanner while driving around. Some of the interference was coming from cable lines quite some distance from my car.
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Old 02-08-2018, 12:52 PM
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Originally Posted by mmckenna View Post
You could call the cable TV company, but you could also drive rusty wood screws up under your finger nails. Each one would be about equally pleasant and have the same general outcome. The Cable TV company should be able to come out and diagnose this, but the random tech you get usually isn't very good at it.
Unfortunately, that's been my experience as well. I've kicked cable techs out of my house more than once when things get too stupid. I've even tried to "hand hold them" through a problem in person but to no avail. Until some over the cable programming needs to be done, I'll deal with things myself.
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Old 02-08-2018, 1:03 PM
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If your signal is getting in, then theirs is getting out as well.

No idea what freq. are in use anymore. But if someone can supply them some hand held searching would be a good start.

Or find a buddy with a spectrum analyser.


Ham friend used to be the top tech. on the local Time Warner system. He would spend an allotted time running routes looking for leaks, would also investigate leak reports. TW also had a special crew that would help if needed, but that was years ago.
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Old 02-08-2018, 1:06 PM
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Or find a buddy with a spectrum analyser.
A RTL-SDR on a USB extension cord + SDR# works pretty well for locating stray RF sources, as long as you have a rough idea of the frequency range of interest.
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Old 02-08-2018, 10:04 PM
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Xfinity (they changed the name because Comcast is so hated?!) like all cable operators, knows that old cables, poor connections, bad grounds, and not installing optional filters all add up and make for RF problems.

They also know what has to be done to pinpoint and fix this, but sadly they just send out contracted techs who get paid peanuts for the fastest cheapest job. In order to get a genuine Comcast employee out to your home and do a real job? You'll need to call up, complain, endure the first wasted visit, call back and escalate the issue, "lather, rinse, repeat" until you get some progress from them. It takes persistence and social engineering to get a real tech these days. But sometimes you get lucky, and the first guy to come out will say it needs a complete premises rewiring...which they may do for free if the problem is really a lousy prior install.

You may still fix it faster & better yourself--but your overinflated cable bill does entitle you to call them up and say "COME FIX". Might as well help employ the underpaid cable contractors.(G)
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Old 02-09-2018, 5:06 PM
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As a rule, TVs are pretty well shielded these days and certainly RG-6
coax is 100% shielded as well.
.....
HDMI cables come in various quality shielding and I've seen some pretty poor shielding on the cheap ones.
.....
You may be able to zero in on the weak point by using a hand held on low power and putting the antenna near the cable box, tv, and hdmi cable while transmitting.
......
Signal levels feeding the cable box should be high enough to overcome most interference sources if the cable guy made sure the levels were high enough.
......
And if used with a coax jumper to the TV, the signal level should also be strong enough to avoid interference.
.......
A marginal signal level feeding the cable box could cause signals to drop during rf ingress.
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Old 02-09-2018, 5:23 PM
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Unfortunately, that's been my experience as well. I've kicked cable techs out of my house more than once when things get too stupid. I've even tried to "hand hold them" through a problem in person but to no avail. Until some over the cable programming needs to be done, I'll deal with things myself.

I had my attic insulated a few years ago. R40 plus. It is piled up over the ductwork and working just fine. So the cable guy comes out and insists on looking at the attic.

I tell him, I have insulated and don't want anyone trampling the attic insulation. You can look, the cable drop is coiled by the hatch and if you think there is excess, you can work with it right there.

No sooner do I get the hatch open, and he scoots up and proceeds to trample through to the far end of the house.

I dragged him out of there. Turned out the problem was bad wiring in neighbors house sending noise back on the trunk. Something they knew about and should a have fixed before hand. As it turns out, he cut off my neighbors cable and she was not very happy.
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Old 02-09-2018, 5:28 PM
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Already tried that, made no difference or improvement.



Already tried that, made no difference or improvement.



There is no loose metal anywhere near the antenna.
Single point bonding and grounding of the affected equipment might be the solution. none of this new requirement has a protective ground. You need to find a screw that attaches to the internal metal chassis on your cable box and TV and bond to ground with a 16 gunge stranded wire. Same for you ham gear. The subject is SINGLE POINT GROUNDING AND EQUIPMENT BONDING.
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Old 02-09-2018, 5:45 PM
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I had my attic insulated a few years ago. R40 plus. It is piled up over the ductwork and working just fine. So the cable guy comes out and insists on looking at the attic.

I tell him, I have insulated and don't want anyone trampling the attic insulation. You can look, the cable drop is coiled by the hatch and if you think there is excess, you can work with it right there.

No sooner do I get the hatch open, and he scoots up and proceeds to trample through to the far end of the house.

I dragged him out of there. Turned out the problem was bad wiring in neighbors house sending noise back on the trunk. Something they knew about and should a have fixed before hand. As it turns out, he cut off my neighbors cable and she was not very happy.
Yeah, it's pretty frustrating when you try to explain things to them and they don't bother to listen, even when it will make their job easier. They shouldn't be making your life harder. I had a similar problem with the phone company many years ago. When trying to repair one of our phone lines, they disconnected a neighbor down the street. They couldn't get it right after several trips. I had go down the street to an underground vault in front of my neighbors house to put us both back together again.
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Old 02-09-2018, 5:56 PM
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Yeah, it's pretty frustrating when you try to explain things to them and they don't bother to listen, even when it will make their job easier. They shouldn't be making your life harder. I had a similar problem with the phone company many years ago. When trying to repair one of our phone lines, they disconnected a neighbor down the street. They couldn't get it right after several trips. I had go down the street to an underground vault in front of my neighbors house to put us both back together again.
For years my AT&T phone was apparently connected at a DEMARC at a neighbors house. They moved, someone new moved in, plugged in a phone and all of a sudden they are on my line. I have to wonder if my phone was being tapped by the original occupant. There are no working spares in the cables in this 40 year old neighborhood. I gave up on AT&T because they could not make DSL work and every repair on the trunk line made it worse.
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Old 02-09-2018, 9:05 PM
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Have them check for broken braid on the coax at the pole.

From flexing in the wind it will break and everything will be normal EXCEPT it will then be HIGHLY sensitive to nearby transmitters even in Police/EMS/FD vehicles etc.

If you have a good camera on your cell phone, you can zoom in as much as possible at the pole to take a photo.
Then, zoom in even further when you look at it on your computer.

You may be able to see a break.

Rich

Edit:
If you have access to a handheld transceiver (even FRS), see it you can find a place in the house where it will generate interference.
Although, less likely with the lower power of FRS.
But worth a try anyway.

Last edited by rbm; 02-09-2018 at 9:21 PM..
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