Another repeater antenna question - UHF Dipole

[DylanMadigan]

I was looking at this and this,

Being relatively new to the radio world, I was wondering if I would see all that much of a difference between these two antennas. I do see that the radiation pattern is half as wide on the more expensive one, but does that mean much of a signal improvement? Like it would be worth the cost?

I was also wondering if this antenna would be safe to leave plugged in during a thunder storm or if I would still have to worry about the repeater (and everything else) melting violently. I do have a lightning arrestor on the line near the base of the tower, but its $20 from ebay so I'm not sure how well it would actually work. Some sort of little gas thing. I was told that if my current antenna was hit, the arrestor wouldn't stop a surge from hitting my equipment.

 

[mmckenna]

I was looking at this and this,

Being relatively new to the radio world, I was wondering if I would see all that much of a difference between these two antennas. I do see that the radiation pattern is half as wide on the more expensive one, but does that mean much of a signal improvement? Like it would be worth the cost?

Both excellent antennas.
A 6.6 to 9.2dB jump would likely show an improvement in coverage, depending on the install location. Antennas like these work best when installed at an appropriate high site. Probably not something you'd want to spend your money on if you were using this at home. The additional gain and associated radiation patterns work well when the antennas have a high enough view to have line of sight out as far as you can. If this will be installed on your home with a moderately sized tower, it's unlikely you'd get enough elevation to really enjoy the benefits. However, higher gain could help with building penetration close in around the repeater.

I was also wondering if this antenna would be safe to leave plugged in during a thunder storm or if I would still have to worry about the repeater (and everything else) melting violently. I do have a lightning arrestor on the line near the base of the tower, but its $20 from ebay so I'm not sure how well it would actually work. Some sort of little gas thing. I was told that if my current antenna was hit, the arrestor wouldn't stop a surge from hitting my equipment.

As with so many things, the answer is "depends".

I'd not trust any of my equipment to a $20 lightning protector.

Lightning protection is only as good as your ground system. For a repeater site, you'd really want that properly designed by an engineer. To do that, they'd have to look at a lot of variables.
So, no one would be able to accurately answer that.

A properly designed grounding system can withstand a lightning strike, broadcast and public safety systems do it all the time. On a hobby/amateur level, it's often beyond the knowledge and capability of the individual to achieve that. You'd have to have a really well designed system to do it right, and that gets expensive.

 

[DylanMadigan]

It would be on a tower about 50ft at home, which is just above 99% of the trees we have. The ground elevation there is about the same as everywhere else, we live on a flat area, with the site being a couple miles from the ocean.

A couple guys told me i should have a couple ground rods 10ft down spaced out around the base of the tower, i put in 4 to be safe. the base of the rods are near water level which I've been told should help allot too. So I think my ground is good.

What would you say I should expect to pay for a good lightning protector?

 

[mmckenna]

It would be on a tower about 50ft at home, which is just above 99% of the trees we have. The ground elevation there is about the same as everywhere else, we live on a flat area, with the site being a couple miles from the ocean.

While I love a decent antenna, and these certainly qualify, I'm not sure I could justify spending $1400 for an antenna that's 50 feet above average terrain. Your distance to horizon is going to be pretty low, so a super high gain antenna like that might be wasted.
I'd probably consider something a bit cheaper. The 6dB gain model will probably work just fine. Then again, if you've got $1,400 burning a hole in your pocket, the extra gain will probably help with building penetration and picking up portables in poor coverage locations.

Also, before spending that much money on an antenna, make sure your coaxial cable is up to snuff, you are running high quality duplexers, etc. No purpose in hoisting all that into the air if you are just going to lose the improvements in low grade coax. I'd be running 1/2" Heliax or better on an application like that. For my 800MHz stuff on installs like yours, I have 7/8" Heliax.

A couple guys told me i should have a couple ground rods 10ft down spaced out around the base of the tower, i put in 4 to be safe. the base of the rods are near water level which I've been told should help allot too. So I think my ground is good.

For a commercial application, there's a lot more that goes into it. The number of ground rods required will depend on the soil conductivity, and you need a specialized piece of test equipment to measure that. You need low resistance grounds to transfer the energy of a strike into the ground. Not enough ground rods and it's going to find different paths.

Doing it right really depends on a lot of factors, and that's where having an engineer design the grounding system matters.

However, I will say that it sounds like you have a better system than most. There's a lot of members on here that don't understand grounding and will either hammer in a short rod, or will skip grounding all together with some misguided notions that it "attracts lightning".

What would you say I should expect to pay for a good lightning protector?

Price out a new PolyPhaser. Usually in the $70 range. Those are common in the industry.

For my public safety stuff, I keep spares on hand. I usually order one and a spare for any application. They can/do fail and will need to be replaced after a strike or even after a nearby strike.

 

[bill4long]

I was looking at this and this,

Being relatively new to the radio world, I was wondering if I would see all that much of a difference between these two antennas. I do see that the radiation pattern is half as wide on the more expensive one, but does that mean much of a signal improvement? Like it would be worth the cost?

I was also wondering if this antenna would be safe to leave plugged in during a thunder storm or if I would still have to worry about the repeater (and everything else) melting violently. I do have a lightning arrestor on the line near the base of the tower, but its $20 from ebay so I'm not sure how well it would actually work. Some sort of little gas thing. I was told that if my current antenna was hit, the arrestor wouldn't stop a surge from hitting my equipment.

For a 50ft home repeater, get a Diamond X-300 for your antenna and forget about wasting money on commercial antennas. Those commercial antennas are great but utterly unnecessary unless you're really to put up a "pro" system, with all that entails, and going for wide area coverage at several hundred feet up.

Polyphasers work nicely for close proximity hits. But a direct hit on any system, and the system is going to suffer severe damage. Anything directly hit is going to be destroyed. Period. I always unplug my coax during lightning storms on all of my radios and my home repeater. If you really want to step up and be a "pro" level repeater system, it's going to cost you a lot more than you probably have in mind. Waste of time and money in this day and age of amateur radio. But if you have the spare cash, go ahead and get it out of your system if you need to.

 

[alcahuete]

As has been said, don't bother, unless you just have money to burn. Just get a reasonably good ham antenna and call it a day. One of my repeaters is an intentionally low-level machine, with a Diamond X-510 up about 30 ft. and I still manage to get 60 miles out of it here in the flat desert. Could go plenty farther than 60 miles, but I go over a mountain at that point, and it barely reaches the other side. Of course, it's also with a good Motorola repeater, quality duplexer, and 7/8" heliax.

 

[W5lz]

Grounding

Ground rods do not do as well as a good radial system. Radicals provide more surface area contact with dirt, so more dissipation area.

 

[jim202]

A little info on ground rods. If you have ever been involved with either a Motorola tower site or a cellular tower site they all generally follow the same guide lines.

First of all there is what is called a cone of influence around a ground rod in the soil. This is normally a radius of half the ground rod length. If you plan on putting in multiple rods, it is best not to overlap the ground rod spacing so you can get the max benefit from each ground rod. A simpler explanation is to space the ground rods twice their length apart. So if you use 10 foot ground rods, space them 20 feet apart.

If your trying to use multiple ground rods for your tower, then you will need to attach the ground wire to the tower leg and run the wire out away from the tower to obtain the needed spacing.

Another issue is that you don't want to attach the ground wire directly to the galvanized tower leg. You really need to use a bronze clamp and attach the ground wire to the bronze clamp. The reason being is that the copper wire, even if it is plated, will cause a galvanic action that will leach the zinc out of the tower plating. This will eventually cause the tower leg to rust and then cause problems.

The last comment is the Motorola ground specs spells out to use a number 2 solid plated copper wire. You can get this at your favorite Lowe's or Home depot in the electrical section. They should also have the bronze clamps to isolate the copper wire from the galvanized tower leg. Just make sure the clamp you pick up will take the copper wire that you plan to use. Also, make sure the bronze clamp you pick up will fit the tower leg your trying to ground. They come in different sizes, so just a heads up.

No sharp bends in the ground wire going to the ground rods. Try to use about a 6 inch radius for the bends.

One last comment about ground rods. The length of the rods you will need will depend on what your soil conditions are to determine how long they need to be. if you have sandy soil, you might have to go way down to get a low resistance ground. I have seen in sandy conditions, that the ground rods needed to be on the order of like 40 feet. If you have clay soil, you can get away with the 8 or 10 foot long ground rods.

Where I live, we have the red clay. Trying to drive ground rods into it is not easy. But I learned a trick. Dig about a 6 inch dia. hole about 6 inches in depth. fill it with water. Come back in about 15 to 20 minutes when the hole has drained. Take your ground rod and push it down by hand as far as it will go. Fill the hole up with water again and then start pulling on the rod and push it back down. You only need to go maybe about 6 inches at a time. You will find you can almost get the entire length of the rod into the ground this way with out beating on it at all. Just keep adding water to the hole as needed. When you get it down all the way, pat yourself on the back and go take a break before doing the next one.

If you have hard pan soil, good luck. But you might still try the water trick and see if it helps. Those of you that live in the northern states where you have ledge, you might end up laying the ground rods horizontal to try to get a ground. In that type of soil, it is not easy. Been there and done that on a couple of mountain tops. In the old days, Bell South and AT&T would lay long runs of wire along the top of the rock and down over the edge until they found some soil to bury the wire under. If you ever find an old AT&T Long Lines tower, look around and you will see what I am talking about if the wire has not been stolen.

If you really want to do some reading, you can do a search for the Motorola R-56 ground specs and enjoy the reading. It is a well wrote document and has a wealth of good information. If you look around long enough you should be able to find a site to download it for free.

Jim

 

[W5lz]

Dirty trick

Use hard drawn copper pipe. Connect water hose to the top end. Turn on water point it down and it will dig it's own hole. You will get wet and dirty. Works for me!

 

[prcguy]

I don't think you want to water drill a hole bigger diameter than the ground rod, you want the rod to be a tight fit with lots of surface area to the soil.

There is a commercial ground rod pounding attachment for hammer drills. This works great and the heavier the hammer drill, the easier they go in. Just pull the trigger on the hammer drill and watch it go.

Otherwise many people have or know someone with a bar bell weight set where you have individual weights that slide onto a bar. You can make a slide hammer using about 2ft of galv steel pipe that these weights will slide over, then use a threaded mounting flange on one end for the weights to rest on and a pipe cap on the other end.

Stack as many weights on the pipe as you can handle, slide the pipe with weights over the ground rod where the pipe cap bottoms out on the end of the ground rod, then lift the pipe and let it slam down on the ground rod. You can get a 10ft ground rod done in about 5 min with this method. Its best to pack the pipe cap end with some large flat washers to take some of the beating because most pipe caps are made in China and the ground rod can sometimes blow though a cheap pipe cap.

Dirty trick

Use hard drawn copper pipe. Connect water hose to the top end. Turn on water point it down and it will dig it's own hole. You will get wet and dirty. Works for me!

 

[WA0CBW]

As prcguy said ground rods need to be DRIVEN into the ground, no water tricks or other methods are acceptable. This provides maximum contact between the rod and the ground. The ground resistance should be less than 10 ohms perferably 5 using the 3 point fall of potential method or a clamp on ground resistance meter.
BB

 

[Lauri-CoyoteFrostbite]

Dylan, the issue of lightning 'arresting" is involved. Approach it scientifically.

Here is a place to start your research...

http://lightningsafety.com/nlsi_lhm/IEEE_Guide.pdf

It's a booklet by the IEEE and, I think, is the best launching platform for a highly technical-- and emotion filled- subject.



Lauri

 

[WA0CBW]

Another source of grounding information is Motorola's R56 manual available on line.
BB

 

[prcguy]

In my opinion, whatever that's worth, I say its nearly impossible for a home owner or renter to make their amateur or scanner antennas and equipment safe from a direct lightning hit. To think you can buy a few arrestor do dads and drive in a ground rod and survive is foolish and dangerous. My best advice is to ground to the National Electrical Code and know you are not protected from a direct hit and take other precautions like disconnecting antenna cables and keeping them far from anything during a storm.

With that said, its very possible to design and build a lightning proof system but the cost of engineering, excavating and parts are probably way beyond what most people could afford, plus you will probably change the look of your house or landscaping in the process. The only way to build such a system effectively is when the house is being designed and built with lightning protection as part of the design. Even though a well engineered and installed system might allow your equipment to survive, most antennas will be destroyed by a direct hit.

 

[W5lz]

In this area water drilling works just fine. Give it a couple of days and that rod is not loose at all. You will not be able to pull it out...

 

[radioman2001]

Partial Quote"
some misguided notions that it "attracts lightning".

The only thing I say is to protect your equipment as best as you can afford. Making your home office or whatever totally lightning proof has some disadvantages. As a Fire Investigator I have seen all kinds of lightning strikes in homes and bussiness that you never would have thought should be hit. There is one home in particular that was hit constantly numerous times a year, year after year, then after many years the owners pulled all the lightning rods, and grounds out and off their home. They then went nearly 20 years before being hit again. By being the center of what lightning sees as a good ground they were actually pulling the lightning to their home instead of it finding some other ground.
My home is protected with all home surge protector, electrical code grounds and a 70 ft tower on the property connected to a 250 ft deep well casing.
BTW as has been said there is no protection from a direct hit, since lightning will go where it wants and not necessarly to your grounding system. That has happened at least twice in my home over the last 25 years. Recently it hit a tree 50 ft from and lower than the tower 70 ft from my home, down and out the roots (tore up the lawn) back up the home ground rod through the electrical panel and out the power company's neutral line. What a surprise since I was in the basement in the middle of replacing the electrical panel to a 200 amp service. The spark that went accross the basement was about 18in. Needless to say my ears hurt and I went back upstairs for a tall hard drink for a few hours.

 

[mmckenna]

Partial Quote"
some misguided notions that it "attracts lightning".

The only thing I say is to protect your equipment as best as you can afford.

I won't argue with that. I hear what you are saying, though. If your antenna is going to get hit, you do want to give it a path to ground. Avoiding proper grounding isn't going to do anything to protect your home or equipment.


As for lightning strikes, I was on a ship that was hit. Didn't take out the radar, HF, VHF, or any of the other radios we had. Didn't even damage anything on the bridge. Did blow out an engine management computer all the way down in the engine room.

Lightning doesn't play by our rules.

 

[jim202]

I wish those of you that keep making the statement that you can't survive a direct lightning strike would stop saying that.

Being involved in the cellular field for many years and also with the public safety radio systems for even longer, yes you can make a radio site able to continue functioning even from a direct strike.

I was at a tower site one rainy day that was using a 500 foot tower. Both cellular and public safety as well as a couple of ham repeaters were all on the tower. The rain was a typical heavy downpour with visibility down to about 50 feet. Not wanting to get drenched from the rain, I sat in my vehicle till the rain would stop. We were having a normal thunder storm rolling through and it was banging fairly frequently. Then the ground shook and I looked at the tower. It was steaming from the heavy current that went through the tower legs from the direct hit.

After the rain stopped, I got out and went into the equipment shelter. Everything was just purring away like nothing had happened. But there was one cabinet over in the corner that didn't have any lights on it. It was one of the ham repeaters that the owners just refused to connect it up to the shelter grounding system and install a good surge protector in series with the coax cable where it came into the shelter.

I rest my case on surge protection and grounding. Think about it a little. If you can't survive a direct hit, how come all the commercial TV and radio stations around the country seem to stay on the air during bad thunder storms? Then there are all the cellular equipment shelters around the country that stay up and functional after all the lightning has left the area.

Yes it does take an effort to put that protection in and it does cost a few bucks to do it. But it works. It is a proven fact that you can survive a direct hit. You just need to know what has to be done and how to install that protection. It takes more that a single ground rod. It takes more than just grounding your coax cable to the site grounding system.

You not that I used the word system. No one thing like a single ground rod makes a grounding SYSTEM. Pleas try reading the Motorola R56 standard. It contains a wealth of information as has already been said.

Most ham radio operators just don't understand that you need to put surge protection in at your main electrical panel. You also need to put in a surge protector on the telephone line. Both need to be installed as part of the protection system. Plus the utility ground rod needs to have a good ground rod and not one that is say 5 years or older. As time goes on, the ground rods do loose the low resistance they are needed to have due to the soil conditions causing them to corrode. Some soil conditions will cause this corrosion to happen faster than other soils.

This is not rocket science to to protect you dwelling and equipment. It just takes a good understanding on how to make a good grounding SYSTEM.

Jim

 

[Lauri-CoyoteFrostbite]

.........Lightning doesn't play by our rules.

.
Oh, so very true.
Fearing this may start a series of lightning anecdotal postings- I will, never the less, throw out my latest Lightning Story.

I have seen lightning in all its quirky behaviors- from enduring multiple strikes a-perched atop an insulated stool at a mountain top research station, to seeing St. Elmo's Fire glowing about my earrings.... a wall blasted out of a remote equipment hut, innocently leaving the contents unharmed- to vapourizing the entire contents of a equipment van- with no entry port detectable.

The agencies I've worked with use the most extensive, through static ("lightning") suppression techniques that tax payer's money can buy.... and yet I can say with all candor, they may protect against the majority of indirect strike- but when "The Big One" has your name on it, all bets are off.

But rest a little easier, a direct strike on a home is very unlikely.

.

That said---

Last summer, on a walk above my mountain home, I was perplex'd momentarily by the disappearance of my favorite trail-side shade tree.
----I had just been up to that spot not more than 24 hours before.

That tree was gone !- completely gone !..... only some roots sticking above the ground remained.--
There were no blasted branches, no pieces of trunk, no charred bark-- Just Gone !
.
Made me think of what my fate would have been, had I been there when that happened.

"Hummpf.....Lauri....Heap gone !"

_____________________________________________________

Friends, family and associates, often ask me why I will (usually) take along a little corn pollen in the summer to offer to Tó Neinilii - the Navajo God of Rain-- asking that he leave Lightning behind when we up into the High Places....

..................Seems to be working.


Lauri
.
.

 

[radioman2001]

Quote"
I wish those of you that keep making the statement that you can't survive a direct lightning strike would stop saying that.

When you are protecting a 200 ft or more tower, the tower can take care of itself you are just protecting the equipment inside the building. Broadcast antenna have a ground running from the top spike right through to the tower or maybe even the static disapaters on top of it. When you are dealing with a wood frame house there is no comparason so saying that you can withstand a full on direct hit is B.S. with any kind of protection. Apples and oranges.

True story: The Alpine Tower in New Jersey was the home to Maj. Armstrong and his early work on FM radio. That tower was hit hundreds of time a year until they installed these static disapaters. The only time it was hit after that was when one of the disapaters fell off from wind. The lightning struck the bracket that held the disapater.
I have had equipment on that tower for over 35 years and have never had a failure of my equipment due to lightning. The tower takes the hit not the infrastructure.

Armstrong Tower - Wikipedia