Does CB Still Interfere With Digital TV?

[gmclam]

Cb

"Can I get some expert opinions?"
You see where THAT got you, now you need answers from experienced CBers. (;->)

I happen to be someone with an extensive background in TV production/broadcasting, cable TV and a former "CBer".

If the OP's CB is getting into a nearby cable system I'd start wondering WHY?! Is the OP running within legal power limits? Is the OP's transmitter in proper working condition? If so, then I'd say go ahead and broadcast and be prepared to defend yourself when Uncle Charlie comes knocking at your door.

I remember back when I was active in REACT and a group of us monitored scanners at a local AM radio station. It was a co-operative effort to acquire real-time information about what was going on, mostly during peak drive times. There was a recording studio next door to the radio station and every time we transmitted on the radio station's legal CB we were heard as clear as day next door.

 

[kb2vxa]

Relax GM, the word is "sarcasm" otherwise known as blood from a dead horse.

 

[gmclam]

Relax GM, the word is "sarcasm" otherwise known as blood from a dead horse.

Sarcasm is OT.

 

[kc4jgc]

Since you say cable 5 in your area is the local origination channel, it's the source of programming. They are not recieving the programming from another location. To reiterate what everyone has said, as long as you have a LEGAL station, you shouldn't have anything to worry about. If you are somehow getting into their system, it's THEIR problem. If you're that close to the head end either (a) their equipment is shoddy or (b) there is a BAD ingress problem, which isn't likely but possible if the CATV company has a bad record of leakage. To be heard that way over a wide area, the wires would have to be hanging bare. If you are being heard all the communities you CATV company serves, I would say (a) is most likely.

 

[jbantennaman]

Hi everybody,

This is my first post, so please be kind.

I am not a expert, but a uncle of mine is, I could ask him if you wanted and he could give you a real answer.

I have a lot of experience with Over The Air reception with Digital Television.

So here is my answer.

The answer is no.

The reason my answer is no is really simple.

First off, most head ends for CATV and Dish type networks uses a hard wire system where there is a direct fiber optic cable that is ran directly from the television station to the head end for what ever type of broadcast they are doing, be it dish or CATV. There is no way for your simple AM CB radio to interfere with their complex system. Even if they did not have a signal hard wired directly to their system, most times they use some type of UHF signal - microwave that sends the television signal to the head end and is not on the same frequency as the television's virtual or actual number.

At the same time, the CATV system is shielded and it's pretty hard to get your signal inside of a shielded coax wire.

The real thing about it all is that Digital TV is not transmitted the same was as Analog TV.

Analog television basically had two transmitters, one for the video which was AM and broadcast at a very high power due to the fact that AM is more susceptible to noise. The video was broadcast on FM with a much lower power level. Internally at one time the video was processed from the tuner at a frequency of 27 Mhz - the same frequency as your CB radio. The early black and white televisions would over load and the picture would black out and you could possibly hear the person talking on the CB radio if the transmitter was close enough to your television antenna.

With a digital signal, the signal is all 1's and 0's - just like the binary code inside of your computer.

With most television OTA signals being moved up into the UHF spectrum, the VHF mostly abandoned - except for a few hold outs like Fox, there is not any chance that your 3 watt CB radio will interfere with it.

If you are even running 1500 watts, I highly doubt if they are going to have any problems with you.

 

[zzdiesel]

I let everything go when I opened this thread in 2009. I'm kinda getting that fever again. I've been watching some of the radio techies on YouTube like Snake Radio Customs & Bell's CB. They're getting me in the CB mood again. There is some fancy toys out nowadays.

 

[jim202]

There are some cable operations that do a very poor job of maintaining the outside cable. There are loose connections, corroded connections and unterminated connections. All of these can be a source of problems. The problems can be increased with the wind blowing the cable around.

The cable techs should have a cable leakage monitor in their vehicles and listen for signal leakage as they drive down the road. You can do the same thing with just a simple scanner tuned to the audio frequencies of the lower channels on the cable. If you hear anything, the cable is leaking too much.

Problem today is that many of the cable companies don't want to spend any extra money and as such, you won't find these receivers in the service vehicles. Sort of rolling the dice and waiting until someone complains or the FCC comes knocking on their door.

I can attest to the issue first hand. Some years ago there was a complaint against a cable company. The cable company chose to do nothing. More complaints were filed and again they did nothing. The FCC got wind and came out to do some snooping. They found excessive leakage in many locations in their cable area.

The FCC field agent called the service office and gave them one hour to have the manager show up at the cable head end. He didn't show up and the FCC agent pulled the electrical meter feeding the head end building. Sat there until someone showed up to find out why the entire cable system went off the air.

The service tech made a phone call and it wasn't that much longer before the cable system engineer showed up. He was given the riot attack by the FCC field engineer and was told the system was going to receive a notice of a fine for not maintaining their system leakage.

That same day, the bucket trucks were out and working on many of the bad connector joints in the cable system. Yes you can get the problem of signal leakage fixed. If the signal is getting out, it can also allow unwanted signals in.

This may have been an extreme example, but there are ways to poke a cable company into submission. Just be polite and don't call them stupid or raise your voice. The poor individual answering the phone is just that. They don't have a clue what your trying to tell them in most cases.

 

[PACNWDude]

CB doesn't interfere with my TV.

None of my TV's or digital receiver boxes are interfered with from my CB radio gear. Granted, I am only running 5 watts, well a bit less actually coming out of the antenna. No linear amplifiers, and the antenna is about 30 feet from the radio, so there is some loss.

UHF does cause some of my dimmable fluorescent lights to flicker though, it messes with their electronic circuits. But that is UHF and about 35 watts output a few feet away from them.

I had a Plasma TV a few years ago, and it was not effected by any of my radio gear. It was about 6 feet away and never had radio audio out of the speaker, flickering or messed up signal due to any transmitter I was using.

Usually I am only putting out 25-35 watts on UHF or VHF, and 5 on CB. I also listen more than transmit. There is a large state ran Emergency Management building about 6 blocks away that has a large HF antenna farm, and it doesn't interfere either. A Verizon cell phone tower next to that has been said to cause complaints for those in an apartment complex next door, but that is just rumor.

 

[prcguy]

The main reason CBs used to interfere with TV is because the 2nd and 3rd harmonic from a CB transmitter landed on TV channel 2, 5 and 6. Adding an amplifier to a CB usually made things much worse.

After the big digital transition was over VHF TV channels 2 through 6 moved to UHF in all but a few areas plus most people are on satellite or cable, which is not susceptible to fundamental or harmonic radiation from CB radios.

An earlier post about TV stations sending programming to cable or satellite providers via fiber is partially true, they do but on a much smaller scale than picking up the signals over the air like everyone else via antennas. Cable TV head ends are still susceptible to interference, just not from CBs due to reasons above.
prcguy

 

[zzdiesel]

I got caught by my 1st wife in 1978 sitting out in the mobile flirting with a younger sweet thang. We lived in the country & had a TV antenna up. She was watching Ch 5 & come to find out she was hearing every word I said. She came out of the front door and needless to say I was under the doghouse.

 

[Orbieswar]

Put the antenna up but no radio.... Wait to see if anyone complains... And yes some do.. simply because you have an antenna up. I did this for two months. Just the ant and no radio.. I got a couple of queries I told them it was for a receiver.... Now I have my radio all up and running.. No one has said boo to me....
It has been over 2 yrs and no issues... Not even with my own TV.

 

[RC286]

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?

The issue isn't being close to a transmitter, its being close to an overly sensitive receiver or a receiver with poor rejection and RFI filtering.

Digital TV is a bit more complicated than the old analog broadcast signals.

You more than likely wont interfere with any digital TVs just because digital is much different than the old AM standard. AM was subject to all kinds of interference where for example, FM is not. This is because much man made and natural noise is amplitude modulated to some respect. FM receivers do not freak out from this kind of interference due to a circuit in the RF stage called the limiter. The limiter does exactly as it is called, it limits the amplitude of the signal, and paired with the AGC (automatic gain control) the receiver effectively either amplifies or attenuates the signal so the amplitude stays constant, eliminating RFI from AM sources. This is also why when receiving the old NTSC tv broadcast signals, you could have a horrid unreadable picture and perfect audio since the video was modulated in AM and the audio was FM.

The new method uses COFDM which is a form of frequency division multiplexing. this allows multiple channels (or streams) to be transmitted on one carrier. (you will notice channels having an actual channel that corresponds to the old TV channels either VHF or UHF and a virtual channel that your tuner will display this is due to the COFDM multiplexing multiple streams that are - don't quote me here but I believe it is QUAM (Quadrature amplitude modulation) - Which is a function of Phase modulation (similar to frequency modulation) and amplitude modulation that allows multiples states as opposed to just binary 1 and 0 , plotted similarly to a xy graph is plotted using the Cartesian coordinate system). These mode as they are, are immune to RFI from AM, add error correction algorithms into the mode AND into the video/audio codecs, and you have quite good rejection of noise and unwanted signals.

Check out your local frequency allocations for DTV, they may not even be in the VHF band anymore, as I recall the FCC is looking to relocate that spectrum to something else, also a good chunk of the UHF band in the 700Mhz range has been relocated for cellular use. Chances are the signals are up in the UHF range, and if they aren't it is highly unlikely that your CB will interfere.

If you are still worried, throw one of these on the output of your radio
TVI 30 LOW Pass Filter | eBay
That is very similar to the Jana HJ-8027 I use for my CB and 10m rig, just because. I wasn't aware of causing any interference, but I felt like putting one on there just as a piece of mind. Granted I only paid $3 for mine at the local HAM flea market.

I say don't worry about it. Set er up and have fun.

-73 VE4BDE

 

[zzdiesel]

Thanks RC286

 

[LoyalServant]

Put the antenna up but no radio.... Wait to see if anyone complains... And yes some do.. simply because you have an antenna up. I did this for two months. Just the ant and no radio.. I got a couple of queries I told them it was for a receiver.... Now I have my radio all up and running.. No one has said boo to me....
It has been over 2 yrs and no issues... Not even with my own TV.

This has been my suggestion since way before DTV was even a reality.

I would tell people to put the antenna up and drop the feedline in a loop hanging down sealed up really well and leave it for several months.

Naturally when people see it go up they immediately blame the presence of the antenna for odd things like their dishwasher failing.... their tires going flat.. or their cat howling at the moon...
(I have heard of a CB antenna being blamed for a dishwasher failure.....)

"I heard that those antennas cause cancer! I am going to sue!"
Until you show them the feedline not connected..... then it's .. oh.....well..... I just don't like it.

There is an industry term we used for them... NIMBYs.

The "big ugly dish" was not immune to being blamed for happenings in the area either.
Garage door won't open... must be that antenna!
On no... it can't be the battery in the remote or simply that it died on it's own.... gotta be that thing that appeared there last week!

 

[RC286]

"I heard that those antennas cause cancer! I am going to sue!"
Until you show them the feedline not connected..... then it's .. oh.....well..... I just don't like it.

If only people knew how much RF they were absorbing just walking down the street. Its like the tin foil hats claiming cell phones cause cancer,.... um no,... well maybe, but they cant be entirely to blame. Since the dawn of radio there has been an exponential increase in wireless communication and RF emissions. TV, cell phones, WiFi, wireless door bells, command stars, car alarms, security systems, video surveillance, GPS, blah blah blah I could go on for ages. We are bombarded with RF 24/7 in increasingly higher levels. Side note, I often wonder if we shut down all wireless communications, how much would the earths temperature drop? I mean, when RF is absorbed it is turned into heat, and collectively there are probably a magnitude of gigawatts of RF being emitted world wide. (remember, it take 500w to reheat your dinner to stifling hot in 7 minutes) Maybe that is the cause of global warming. HAHA!

The issue here is most people think it is their god given right to receive a TV signal, or use their cell phone, they think it should just work. if it doesn't they look for someone or something to blame for it failing to take into account device sensitivity to RF, and lack of understanding of how the technology actually works.

Another thing that baffles me, is hospitals claim you cannot use your phone as a safety measure to sensitive equipment. Hmm well I hardly think my dinky 1W cell transmitter is going to do more damage than the EMS and security personnel walking around and talking on their radios that can very well transmit excess of 10W, hell even 25W in a handheld isn't uncommon for a high end rig.

Well rant done.

My opinion is know your legal rights, your local RF standards and communications protocols, address concerns appropriately and have fun.

I have had people ask me what the random metal crap im putting in the air is all about, or why I spent all afternoon on the roof. I tell them straight up, its amateur radio or CB antennas, some are interested and engage in conversation, others are less than interested and walk away. I have yet to have a complaint about the antennas or interference, or wound up with needles in the coax

 

[PACNWDude]

10-25W in a handheld?

I would like to know which high end radios operate at 10-25 watts. I own some very high end radios, and none of the handheld ones will transmit that much power without an external amplifier.

Unless you are lugging around a military AN/PRC-117F/G and calling it a handheld, I have never seen a radio in a hospital that puts out that kind of power.

Hospital handhelds are usually 5-6 watt VHF Motorola radios. These do not warm the climate as much as many other things mankind has invented.

Before RF equipment and gasoline engines, there was burning coal and steam locomotives. Before that, there was whale oil and wood fires. Times may change, but there is always something that will change our environment, and it is not all able to be changed by us.

 

[prcguy]

Yup, no 10 or 25w handhelds out there. One of the new Baofeng's claims to do 8w but I think that doesn't buy any range over a 5w and the battery life will be worse.

Manpack rigs with some very hefty size batferies as used by the military are the only place your going to find anything more than the 8w Baofeng.
prcguy