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Old 10-14-2009, 8:28 AM
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Default Does CB Still Interfere With Digital TV?

I've been out of CB for several years now. One reason is I bought a house with the local cable TV tower that is about 100 yards behind my property line. I didn't want to broadcast on channel 5 all over 2 towns. My wife seems to think that issue may be gone since digital TV has taken over.

Can I get some expert opinions?
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Old 10-14-2009, 9:17 AM
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Yes, No, Maybe,

Digital does not eliminate interference.

But it can hide it, unless it is bad enough not to be hidden.

Interference is like trying to listen to a conversation in a room with lots of background noise.

Digital is as if instead of listening to the conversation, you are reading a transcription by someone else listening in the noisy room.

How would you describe the difference between "not too much noise" and "too much noise"?
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Old 10-14-2009, 9:20 AM
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So, would you try to run a station in my shoes?
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Old 10-14-2009, 9:21 AM
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It appears that VHF channels 2 through 7 are no longer used in most areas and many have moved to UHF which is much less susceptible to CB interference. Also newer Plasma, LCD and other flat screen TVs are much better shielded from direct interference to the circuit board and up the line cord.

However, if you used to create interference on a neighbors TV on say VHF ch 8 through 13 for some reason and you and your neighbor are using the exact same equipment now as from the analog TV days, there could still be a problem. A digital TV signal can easily be disrupted if your CB and amplifier are producing crap on a TV channel or your swamping the input of the TV tuner due to high power operation in close proximity of the TV antenna .

Audio cables between a TV and stereo are still susceptible to interference as are remote speakers with long speaker leads. High power can still get into the AC power distribution and and cause problems. A legal CB should really have no problems these days.
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Old 10-14-2009, 9:29 AM
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This area has been susceptible to tearing up channel 5 on TV. The cable system now uses it's ch 5 for local origin programming. That might help.

You also made me think about getting on neighbor's audio equipment & etc. I think I just changed my mind.
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Old 10-14-2009, 9:56 AM
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Run a legal station, with a properly installed and grounded antenna and don't worry.

If it causes problems then they can figure out why.
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Old 10-14-2009, 10:04 AM
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TV ch 5 is/was very susceptible to CB interference because its at the 2nd harmonic of CB but I would be very surprised if a stock CB could get into a cable system unless your near the head end antennas.

Some CB antennas radiate downwards more than others which puts more signal into your neighbors antenna and equipment. If your antenna is much higher than your neighbors house and its got ground radials that's a good start. Many stick type antennas are not decoupled from the coax very well and the coax radiates quite a bit.That can bring RF into areas that are more susceptible to equipment.

I run upwards of 1500w on many HF bands and have no complaints from my neighbors. Maybe I'm lucky or maybe my operation does not coincide with their TV time. A stock CB should not be a problem so go for it.
prcguy

Quote:
Originally Posted by zzdiesel View Post
This area has been susceptible to tearing up channel 5 on TV. The cable system now uses it's ch 5 for local origin programming. That might help.

You also made me think about getting on neighbor's audio equipment & etc. I think I just changed my mind.
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Old 10-14-2009, 2:36 PM
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Quote:
Originally Posted by prcguy View Post
TV ch 5 is/was very susceptible to CB interference because its at the 2nd harmonic of CB
Really? CB channel 1 is 26.965 MHz - x2 = 53.930 MHz. CB channel 40 is 27.405 MHz - x2 = 54.810 MHz. TV channel 2 is 54.0 MHz to 60.0 MHz. TV channel 5 is 76.0 MHz to 82.0 MHz.

Quote:
but I would be very surprised if a stock CB could get into a cable system unless your near the head end antennas.
If the OP is running no more than 5.0 watts from a clean radio I might agree. But if the OP is running more power or is very close to a cable reception point, that's another issue.

Quote:
Originally Posted by zzdiesel
I've been out of CB for several years now. One reason is I bought a house with the local cable TV tower that is about 100 yards behind my property line. I didn't want to broadcast on channel 5 all over 2 towns. My wife seems to think that issue may be gone since digital TV has taken over.
Is there only a tower behind you? How about a studio? I have seen/heard CB getting into audio consoles. The modulation is AM and it does not take much to extract the audio component of the RF signal. Especially with cheap equipment, which the cable TV industry is historically famous for using. Can CB interfere with digital TV - yes. Does it manifest itself the same way it did with NTSC? No.
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Last edited by gmclam; 10-14-2009 at 2:40 PM..
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Old 10-14-2009, 2:51 PM
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I should have been more clearer. The tower is back there along with what I think is called the "Head"

It is a building with all the electronics that get the signals from the tower and the Sat dishes and then it feeds out to the system.
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Old 10-14-2009, 2:52 PM
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2nd harmonics are weak. The third is the one to watch out for.
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Old 10-14-2009, 4:07 PM
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Your right TV ch 5 is near the 3rd harmonic, I was thinking of TV ch 2 for some reason.

A legal CB should not cause any problems with a cable head end unless the TV antennas are real close and even then interference would be unusual. If your CB is legal and you have an aftermarket low pass filter and you do screw up the cable system it would technically be their problem. Some areas have laws regarding CB interference and its handled by local cops which is different from amateur radio interference since hams are licensed.

I love the idea of a cop investigating and enforcing RF related problems. That's like sending my mother to investigate a crime scene and arrest somebody.
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Quote:
Originally Posted by gmclam View Post
Really? CB channel 1 is 26.965 MHz - x2 = 53.930 MHz. CB channel 40 is 27.405 MHz - x2 = 54.810 MHz. TV channel 2 is 54.0 MHz to 60.0 MHz. TV channel 5 is 76.0 MHz to 82.0 MHz.

If the OP is running no more than 5.0 watts from a clean radio I might agree. But if the OP is running more power or is very close to a cable reception point, that's another issue.

Is there only a tower behind you? How about a studio? I have seen/heard CB getting into audio consoles. The modulation is AM and it does not take much to extract the audio component of the RF signal. Especially with cheap equipment, which the cable TV industry is historically famous for using. Can CB interfere with digital TV - yes. Does it manifest itself the same way it did with NTSC? No.
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Old 10-14-2009, 8:27 PM
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Quote:
Originally Posted by N_Jay View Post
2nd harmonics are weak. The third is the one to watch out for.
Very true. And the 3rd harmonic does line up with TV channel 5.

CB channel 1 (26.965) x 3 = 80.895
CB channel 32 (27.325) x 3 = 81.975

Quote:
Originally Posted by zzdiesel
I should have been more clearer. The tower is back there along with what I think is called the "Head"

It is a building with all the electronics that get the signals from the tower and the Sat dishes and then it feeds out to the system.
It is called a "head end". There can be more than one head end to a system, and they vary as to how much processing is done at any one location.

I don't know anything about the TV channels in use in your area, or the makeup of what your cable TV system carries. They could be receiving a channel from low power analog and putting that out on their system. There could still be some analog (channel 5) within their head end.

There is another thread here today on RR from a CBer who is hearing himself out of his truck's speakers. He indicates that happens even if he has CD/etc selected (in other words not via radio reception). This goes to my point about how easy it is to get the audio portion of a CB signal (when you don't want it).
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Old 10-16-2009, 5:20 AM
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Exclamation My Two Cents...

If the base of that Head-End tower is only 100ft from the property line, then the actual antenna is farther than that from yours. Those antennas are more than likely high up for good reception. Besides, if you buy cable service, you are still subject to the same reception problems as if you received them for yourself at home. I don't think the quality of television is increased by such a concept, anyway. Just an increase of channels, and the addition of an unnecessary bill.

I think my digital receivers cause more interference with my CB radio, than the other way around. Anyway, higher vhf radios interfere with the same channels using five watts. It's just the nature of the thing.
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Old 10-16-2009, 7:13 AM
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What's the point of owning a CB if you do that? :-)

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Run a legal station.
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Old 10-16-2009, 7:37 AM
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What's the point of owning a CB if you do that? :-)

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Old 10-16-2009, 9:11 AM
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Why all the fuss? These things get so easily out of hand when the techies show off so lets get back to the question and a SIMPLE answer.

The answer is yes but the effect is different, analog is very interference and weak signal tolerant, you can still receive but it's a matter of how well. Digital is an all or nothing proposition, if the signal is disrupted enough or weak enough reception blacks out altogether. The bottom line is if you clobber an analog TV signal you'll get a herringbone pattern on the screen with the picture still visible and you may be heard on the speakers but with digital the screen goes dark and the speakers fall silent.

As for interfering with a cable head end, not likely since the wanted signals are very strong as compared to unwanted due to professional high gain antennas at high altitude. If you run a dirty transmitter, especially one of those nasty POS illegal leenyars the odds change significantly.
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Old 10-16-2009, 1:40 PM
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Quote:
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As for interfering with a cable head end, not likely since the wanted signals are very strong as compared to unwanted due to professional high gain antennas at high altitude.
NOT TRUE! It seems like you are thinking about cable head ends in metropolitan areas. These days many signals are not aqcuired off-the-air but are fed directly by the broadcaster via fiber or other links.

HOWEVER, in rural areas the station which is being received by the cable head end may be quite some distance away and quite weak. Yeah they're using directional antennas, but what happens when the CB is in 'front' of that antenna?

Additionally as I wrote earlier I've seen CB audio (running legally) get into audio mixing consoles and other poorly designed equipment. Cable head ends are usually not just receiving sites, they do a lot of processing as well and a legal CB signal could easily get where it is unwanted.

Quote:
Originally Posted by roadranger
... Besides, if you buy cable service, you are still subject to the same reception problems as if you received them for yourself at home. I don't think the quality of television is increased by such a concept, anyway. Just an increase of channels, and the addition of an unnecessary bill.
The concept of 'cable' TV is to receive a signal that you can get yourself for free. Convert the signal to change its channel and/or reduce its bandwidth (to get as many signals onto the cable as possible). Run the signal through a cable for several hundred feet to attenuate it. Then amplify the signal (which adds noise) and run through more cable.

I worked for a cable company for a few years. It was "interesting" to see what a signal looked like after going through many miles of cable. In older days tricks were used to block convert a band of signals down (to frequencies below channel 2), run them through the cable, and then block convert them back up before getting to the subscriber's home. Oh the processing involved.

With digital-over-the-air we can now acquire the best signal available to consumers at home for free. I've always said cable TV is about QUANTITY, not QUALITY.
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Old 10-16-2009, 1:51 PM
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If a legal CB gets into a cable head-end (sat, fiber or off-air, feed) from 100 feet away, the engineer needs to be taken out and spanked.
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Old 10-17-2009, 10:46 AM
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Hello ZZDiesel: I would think that the interference would be non existent.

You can add in your coax line a low pass filter, (that really attenuates the harmonic RF Energy) and ground the radio, and use a good 5/8 wavelength ground plane antenna, as the non ground plane antennas seem to have more interference problems as compared to the 5/8 ground plane antennas.

I am sure the cable system is pretty tight to being interfered with. I'd say go for it...

Hope this helps.

Jay in the Mojave

Quote:
Originally Posted by zzdiesel View Post
I've been out of CB for several years now. One reason is I bought a house with the local cable TV tower that is about 100 yards behind my property line. I didn't want to broadcast on channel 5 all over 2 towns. My wife seems to think that issue may be gone since digital TV has taken over.

Can I get some expert opinions?
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Old 10-18-2009, 12:37 PM
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"Can I get some expert opinions?"

You see where THAT got you, now you need answers from experienced CBers. (;->)
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