Antennas and grounding requirements

scott784 · 29-Jan-2011, 1:53 AM

I've got an antenna on a mast which goes from the A part of the roof line (clamped down with brackets on the A part of the roof) all the way down to the ground, 30 feet below. At ground level, a separate steel grounding rod was then drove into the ground 5 feet deep with a sledgehammer with an additional several feet of the ground rod sticking up out of the ground. The ground rod was then attached with metal clamps to tightly secure the ground rod directly to the lower part of the anntenna mast near the ground. There's no actual ground wire attached between the mast and ground rod, but again they are tightly connected to each other with the metal claimps and screws. So as I understand things, the mast itself is grounded but the cable and rotator wire (running down the mast) and into the house are not grounded.

Now for my question, if I use a ground block to ground the actual coax cable wire and separate rotator wire, would I lose any of my signal strength? I am picking up some fringe tv stations perfectly and do not want those signals degraded. I only ask this question because it would appear any time a coax cable is cut and then connected back together, it would seem this is possible. The last thing I want is to have an antenna that may attract lightening as we move into the warm months and get thunderstorms. However, as I've said, I don't want to lose the signal strength I've got either. I've been told if lightening ever hits the antenna that it would most likely run straight down the mast and into the ground (since the mast is grounded with a ground rod). So do I take added precautions and ground the coax and rotator wire and possibly lose some of my signal or just leave well enough alone?

GroundUrMast · 30-Jan-2011, 5:04 PM

No, you will not loose signal by grounding the shield of the coax. The grounding block should not directly connect the signal carrying center conductor of the coax to ground. Unless the mast anchor rod is bonded to the rest of the electrical service ground system I would not consider it to be a 'ground' rod.

http://forum.tvfool.com/showthread.php?t=901

scott784 · 30-Jan-2011, 6:20 PM

So I guess you are saying that it's not the same concept of how coax loses signal when ran through something entirely different such as a surge protector. Is that right?

I only ask becase (just the other day) I decided to run my coax (in my living room) inside my Monster surge protector first, and then out of the surge protector to the television. I immediately noticed the reception was no longer as clear as before.

For that reason, I took the coax off the surge protector and now the coax is going directly to the television. I heard someone at Time Warner Cable who also mentioned this (downside) about running coax through surge protectors. And it was confirmed with my own visual look of the channels when I did it myself.

Again, though I know very little about grounding and running a coax through a ground block where the line comes into the house may be entirely different (as it relates to any signal loss). I appreciate any additional feedback.

GroundUrMast · 30-Jan-2011, 6:57 PM

I can only guess at the internal make up of the surge protector, but it sounds like it does connect some type of component to the center conductor of the coax. Common grounding blocks do not.

I'm not against surge protectors... but I don't use them as the primary grounding mechanism of my antenna system.

scott784 · 30-Jan-2011, 7:35 PM

I've got a Monster Power Home Theatre system surge protector, HTS 1000. I was not considering using this as an alternate to proper grounding outside. However, I only brought it up because of the fact that I noticed signal degradation when I ran my coax through it. I was only for that reason that I started to think about any and/or all intermediary devices causing signal loss when you run those devices between the coax up at the antenna and the final point where the coax meets the television. Thanks.

mtownsend · 30-Jan-2011, 8:24 PM

Has your house ever been hit by lightning before?

If lightning is common in your neighborhood, I'd say the best defense is to have a dedicated lightning rod somewhere else on your property (some distance away from your antennas) that extends higher than your TV mast.

Surge protection and grounding of your TV antenna will protect your equipment from *indirect* lightning strikes, but if you ever get a direct hit, chances are that your equipment will not survive no matter what.

Consumer-grade surge suppression equipment might save you from mild spikes (e.g., power grid switching on after a blackout, indirect lightning strikes on power/cable/telephone lines, etc.), but nothing as intense as a direct strike on your house.

In regards to your more general question about signal loss along the coax... Yes, it's possible to have some extra signal loss caused by a junction point in the cable. The amount of loss will depend a lot on how bad the impedance mismatch is at the junction. The loss from splicing two sections of identical coax together is usually insignificant if the connectors and components are built well (~ only a fraction of a dB).

Splitters, directional couplers, baluns, filters, and other frequency-sensitive components are more likely to have impedance mismatches that will cause some signal to be reflected back the way it came. There may also be internal inefficiencies that cause some signal to be lost as well.

The coax itself is also responsible for signal loss over distance.

If your signals are weak to begin with, and you are concerned about every bit of signal loss along the way because you want to preserve as much signal quality as possible, then what you really need is a good pre-amp installed close to the antenna (which I think you already have).

If you have a pre-amp installed, most of the losses downstream from the amp become insignificant and, for the most part, can be ignored. You just need to make sure the gain in the amp is sufficient to overcome the downstream losses that you incur. To maintain the best possible SNR, you'll want your pre-amp to have a low Noise Figure rating.

scott784 · 30-Jan-2011, 9:33 PM

I've only lived here for 2 years and I am not aware of my neighborhood being particularly bad as far as lightening strikes. Of course, in the southeastern US, thunderstorms and lightening can be quite common anywhere around here in the Spring and even more so in the summer.

As for a preamp, yes I've got a HDP 269 12db amplifier on my WInegard 9095P antenna. The antenna is only for one television with no splitters along the way to the house. I've got fringe stations that I can receive. I deliberately used a preamp so I could grab those fringe television stations, along with my other locals.

From your previous comments, I understand any signal loss on a coax will vary based on the device used along the way. As you said, direct coax to coax is very insignificant. On the other hand, as I understand, splitters can cause much more measurable loss--I suppose even with a preamp.

So does a ground block cause virtually no loss? I am gathering from the comments that it is very minimal-perhaps like a good coax to coax connection. Right? I just wanted to fully understand this issue before I break the coax where it meets the house with a ground block.

mtownsend · 30-Jan-2011, 10:48 PM

RG6 coax can lose up to about 7 dB (worst case) for every 100 feet. Actual loss varies with frequency, so lower channels (i.e., VHF) might only lose about 3 dB per 100 feet.

RG59 coax can lose up to about 11 dB (worst case) for every 100 feet.

A 2-way splitter will have about 4 dB of loss. Splitters are also known as power dividers since each output gets an equal share of the input power. When a signal is split two ways, each output port gets 1/2 of the input power. Half power means a loss of 3 dB, but since these components are never 100% efficient, in reality you get somewhere between 3.5 to 4 dB of loss.

A 4-way splitter will have about 7 dB of loss.

An 8-way splitter will have about 10 dB of loss.

The Noise Figure on most consumer-grade TV tuners is roughly 6 dB, although some have been known to be worse (like ~10 dB).

Just follow the chain between the amp and your TV to add up how much loss you are going to have. For example, if you have 4 dB of loss from coax, 4 dB from a splitter, and 6 dB due to your tuner's Noise Figure, you have a total of 14 dB of anticipated loss. Since this is a little more than your amp's 12 dB boost, you might actually be losing approximately 2 dB of net SNR due to insufficient amp gain.

Since you already have the HDP-269, I wouldn't worry about these 2 dB. At the moment, I think you're just feeding 1 TV, so you don't have the 4 dB splitter loss. Even if you decide to add the splitter later, I don't think you'll notice the 2 dB SNR loss, so there's probably no justification to go out and spend money if you don't have to.

I'm guessing that you went with the HDP-269 because you are trying to avoid amp overload on some very strong input signals. The low gain (12 dB) of this amp is one of the reasons it is able to handle higher input levels than most other pre-amps.

For people who have very high losses (e.g., very long cables, 8-way splits, etc.), then there's good justification for getting a higher gain pre-amp or adding a mid-stream distribution amp.

scott784 · 31-Jan-2011, 2:53 AM

You are very smart in figuring out that I deliberately chose the HDP 269 12 db amplifier on my Winegard 9095P antenna to avoid signal overload. I have no plans on using my outdoor antenna on any other television in the house, so I thought a 12 db amplifier was sufficient.

My closest locals are only 20 to 30 miles away. At the same time, I wanted to grab other stations upwards to 70 miles away.

Back on topic, I now need to consider how I am going to proceed with grounding this antenna. Fortunately, we are in the winter but I don't think it's a good plan to keep the status quo as we approach the warmer months.

GroundUrMast · 31-Jan-2011, 6:02 PM

It sounds like you're on track. Just beware of the danger of two or more isolated ground systems on the premise. If you ground something to an isolated rod, it's possible for dangerous voltages to develop between the isolated object and objects connected to the other ground system. If you have added a ground rod anywhere on your property, it needs to be bonded to the existing grounding system. Where I live, the minimum size cable used for bonding is #6 copper.

Mast ground in my area is done with a minimum of #10 copper and coax ground block connections need at least #14 copper.

Investing a beer or two with a local, experienced electrician may produce clear answers to your specific questions, that's beer well spent.

scott784 · 1-Feb-2011, 12:02 AM

I appreciate your reply. I thought it was okay to ground my antenna mast and coax separately from the main grounding system as long as they are sufficiently grounded with the right size grounding wire.

My electrical box and the main grounding system, for the house are a good distance aways.

GroundUrMast · 1-Feb-2011, 12:57 AM

I chose to bury about 40' of #6 copper when I drove a new ground rod out by my garage where the mast is located. I hope it's a complete waste of money - never needed.

scott784 · 1-Feb-2011, 1:24 AM

Doesn't that get really expensive running copper wire for that amount of feet underground to get to the main electrical service system in the back of the house? This is my dilemma since my antenna mast is no where near the main electrical service system.

GroundUrMast · 1-Feb-2011, 2:06 AM

I was able to do the work myself. I recall the #6 copper being about 40 cents / foot @ the big box home center. Just now did an online price check and the first www to come up is asking 73 cents / foot.

The reality is that many people never consider the issue and they get lucky. Only a handful of people ever get hit by lighting. Only a handful of people ever get shocked because something was not grounded properly. Some people resent being told to wear a seat belt...

I'm fairly certain that I am an odd one out for thinking about the subject and spending a few bucks as a result. On the other hand, I'm still saving about $70/mo after ditching "Enhanced Basic" cable service - I have long since passed the point of being in the hole monetarily.

scott784 · 1-Feb-2011, 10:33 PM

As the majority of Americans use cable or satelite now, it seems absolutely amazing how difficult it is in finding a local person who is experienced in things related to OTA antennas! This is a far cry from 30 years ago when I imagine a person could've picked up a phone book and found all kinds of people out there available to do just about any job you might ask for with OTA antennas.

GroundUrMast · 1-Feb-2011, 11:00 PM

Very very frustrating...

scott784 · 2-Feb-2011, 11:14 PM

If I have understood your posts on these boards, you've indicated that merely grounding the coax and mast to the ground rod (right next to the mast) can cause dangerous lightening charges IF the ground wiring is not ALSO tied in with the main breaker box. So if I am understanding your comments, you are saying that without the 'additional' ground wire to the main electrical ground (breaker box), it's all a waste of time? If not more detrimental to the set up?

Unfortunately, as I've said before, I would assume many people are confronted with the exact same issue as I've got. That is, their antenna and mast are no where near the breaker box. (I could not have installed my antenna near the breaker box even if I wanted to because there was not good line of sight back there). On top of that, my breaker box is near power lines.

So I guess I am wondering about the following. If a person can get all that extra length of ground wire installed around the outside corners of their house, how effective is that additional grounding going to be with these sharp turns as well as the distance factor? Also, if this exta ground wire is not used, am I correct in understanding your comments to say that it's a waste of time because of dangerous voltages between what you referred to as two separate grounds (the main one at the electrical box and the separate one at the ground rod)?

There seems to be different schools of thought on this, such as with the following link: http://www.hdtvprimer.com/ANTENNAS/basics.html
(Move down to antenna grounding once you are within that link above).

What are your thoughts on my questions? I appreciate any additional comments you have on this matter. I don't profess to know a lot about it. And of course, most people know next to nothing on this specific topic, to include my electrician guy who came out here yesterday.

GroundUrMast · 2-Feb-2011, 11:53 PM

The link you cite offers an excellent example drawing in the section titled "The NEC requirement". There are two ground rods shown. The ground rods are "bonded" together with #6 AWG CU. If that bond were omitted, the ground rod under the antenna would have a connection to the electrical service ground only through earth (or possibly the tuner in your TV). The real world impedance/resistance a lone ground rod can be anywhere from a few ohms to hundreds of ohms.

Voltage = Current X Resistance. If a fault current flows in an isolated ground rod, voltage will develop. The #6 CU wire can be depended upon to provide a predictable low impedance connection, whereas earth can not. By bonding all parts of the grounding system together with low impedance conductors, the voltage difference between grounded objects (such as the AC neutral conductor powering your television and the antenna coax) will be held to a minimum if fault current flows somewhere in the system.

A difference in voltage will not develop on it's own. An outside energy source is required. That can be from atmospheric static, or from insulation failing - allowing an AC conductor to contact something that should be at ground potential.

The longer a conductor is, the more resistance it will have. #6 CU wire has about 0.4 Ohms per 1000 feet. Going around bends will add impedance at frequencies above DC, but at DC and power line frequencies the increase is negligible.

I very much agree that the grounding wire from the mast, to the the connection to the ground rod, should be as short and straight as possible. If you take a direct hit by lighting, you want to make the path to earth as easy and inviting as possible. Once lighting has found it's way to the ground, stand back and let it go where it wants to.

As mtownsend observed earlier, if lighting is a significant risk in your area, a dedicated lighting rod is something to consider.

scott784 · 3-Feb-2011, 12:50 AM

Thanks for your quick reply. I haven't done the exact measurements.

However, let's say the length (to include going around all the corners of the house) is at least a total of 100 feet from the base of the antenna mast to the electrical power box on the back of the house. What size grounding wire is required for that? How many feet off the ground must this grounding wire be? Must it remain the exact same height around each corner of the house? How is it best secured to a home (vinyl sided with a concrete slab)? What if there are obstacles, such as my back patio with door, or if I ran the ground wire around the other side of the house, how about the front porch as an obstacle? With this ground wire being so long, would it create its own electrical problems? What is the best strategy to use to find a qualified electrician who performs this type of work? What is a reasonable price to pay for all of this ground wire, plus a ground block, and bonding the ground rod (at the mast) to the main electrical system?

Also, this is a follow-up question to what I asked you earlier. Is it your position that a separate grounded antenna/mast (not tied in with the main electrical ground) is worse than no ground at all? I ask that question because of the information you posted earlier about the imbalances it creates when an antenna/mast grounded system is not tied in with the main ground.

That's a lot of questions and you may not be able to answer all of them adequately. However, as you can see, this is the type of issue that the average (non electrical person) like myself is confronted with if I choose to follow NEC code, to the letter.

Lots of complexities, different schools of thought, and unknown costs involved. I guess that's why many people just throw their hands up and forget about grounding (at least when the electrical box is not close by). On a positive note, I've learned a few things along the way by checking into all of this.

PS I forget to mention there's not only a coax cable running down my 30 foot mast but also a rotator wire.

GroundUrMast · 3-Feb-2011, 1:33 AM

If you are hiring the work done, I would ask for firm written bids. In many areas, there is no charge for a bid. I don't know if that's true where you are.

The rest of your questions may be governed by local code. If I were using copper clad ground rods, I would have no reservation against direct burial of solid #6 CU. I would choose a depth and path that protects from damage. But I risk giving you advise that local code would over rule.

http://www.mikeholt.com/mojonewsarch...s~20020701.htm is not the most current reference but does speak to the NEC.