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Message |
    
Capt205
Junior Member
Username: Capt205
Post Number: 21
Registered: 5-2005
| | Posted on Wednesday, July 20, 2005 - 11:26 am: | 
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My setup is....IMAX 2000 on 5 sections of 10'antenna poles, with #6 ground wire running from the antenna U clamp down to an 8' ground rod driven all the way into the ground. The ground rod clamp is clamped around the rod and the antenna pole. A 175' run of rg213 to the house (buried), and through the wall to my Dosy 3001/jumper/amp/jumper/radio. I unplug the coax during thunderstorms and whenever I'm not using the radio.
Question is....do I need to run a seperate ground for the radio, and if so, why? Also what would be the best way to accomplish this?
Does sticking the end of the coax into a glass jar really work? |
Snowfire
Intermediate Member
Username: Snowfire
Post Number: 121
Registered: 2-2004
| | Posted on Wednesday, July 20, 2005 - 11:47 am: |
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Capt205 I have my ground setup simular to what your's is and have not had any problem's. My ground rod is grounded to the tower. My coax is not buried. I don't have my radio and amp grounded together. The glass jar thing I also do, and I wounder if it does work.
Cef 294 |
Tech808
Moderator
Username: Tech808
Post Number: 6387
Registered: 8-2002
| | Posted on Wednesday, July 20, 2005 - 11:58 am: |
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Just one word = PolyPhaser. 
PolyPhaser IS-50 Series REVIEW
Lon
Tech808
CEF808
N9OSN  |
Yankee
Advanced Member
Username: Yankee
Post Number: 748
Registered: 7-2003
| | Posted on Wednesday, July 20, 2005 - 3:03 pm: |
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If you were to get a direct lightning strike you would have pieces of glass flying all about your radio room, therefore the glass jar is not a good idea.
Carl CEF-357 |
Road_warrior
Advanced Member
Username: Road_warrior
Post Number: 698
Registered: 7-2004
| | Posted on Wednesday, July 20, 2005 - 4:36 pm: |
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I personally don't trust any grounding
system. During thunderstorms i water-
proof my connector and place outside away
from house. |
Hollowpoint445
Advanced Member
Username: Hollowpoint445
Post Number: 568
Registered: 6-2004
| | Posted on Wednesday, July 20, 2005 - 6:07 pm: |
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"Does sticking the end of the coax into a glass jar really work?"
It sure does! It effectively turns the glass jar into a fragmenting grenade if you should ever be unlucky enough to have your antenna struck by lightning.
There are some things that could be improved with your system:
The coax shield should be grounded right at the base of your support structure where the antenna is grounded and again just before it enters your home.
The antenna system ground should be connected to your house's electrical system ground to form a single point ground system. The best way would be to create a perimeter ground around your home, and then connect the antenna with as short a cable as possible to the perimeter ground.
Your radio equipment should be grounded with as short a cable as possible to the perimeter ground.
Some sort of coaxial protection should be used to prevent damage to your radio equipment - the Polyphaser device that Lon suggested is a good one.
The above suggestions are for safety alone. For RF grounding - should you need it - all cables should be as wide, flat, and short as possible so RF travels easier on them. Wide copper ribbon is the best, but there are alternatives like flattened copper pipe or copper braid. |
Twowatt
Junior Member
Username: Twowatt
Post Number: 43
Registered: 7-2005
| | Posted on Wednesday, July 20, 2005 - 10:02 pm: |
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snowfire, capt205,
disconnecting, waterproofing and throwing the coax out the window is a VERY good (if not the BEST) idea when the storm is heading your way. but let's assume the lightning is going to pass u by, but u still have a lot of wind and rain. this can cause a static charge on ur antenna that could damage the radio's front end. a simple way to discharge this static voltage build-up is to use a good antenna switch, and instead of putting the radio to the common input of the switch put the antenna to the input. then add a small (2-5w) 50ohm dummy to one of the switch's output conn and put the radio on another output conn. this will allow u to quickly discharge any static build-up on ur antenna.
regards |
Tech237
Moderator
Username: Tech237
Post Number: 166
Registered: 4-2004
| | Posted on Thursday, July 21, 2005 - 8:53 am: |
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I would not ground the coax at both the tower and where it enters the house. Sometimes, due to different ground potentials (don't assume that ground is at 0V) you will produce a circulating current in the coax sheild that will cause you more problems,trying to locate that illusive noise (at the least) than you solve. This problem can also explain some of those unsovable noises you find in a mobile installation. This problem even has a name - Ground Loops. |
Airplane1
Advanced Member
Username: Airplane1
Post Number: 506
Registered: 5-2004
| | Posted on Thursday, July 21, 2005 - 10:58 am: |
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Is`nt that what airplanes do?
Just funning with you!
AP |
Hotwire
Intermediate Member
Username: Hotwire
Post Number: 451
Registered: 1-2005
| | Posted on Thursday, July 21, 2005 - 11:33 am: |
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I have an Imax grounded like yours. Tried grounding the radio too but it did not make a difference anywhere in performance or recieve. The best thing I did to better my recieve was get better coax. Was using the cheaper rg58 and went to mini 8 and now its much better, far less static. As for lightning I just unhook everything and hang the wires over the side of my desk. Now my dad uses the glass jar method to this day. Glass is a good insulator. Lightning has hit his antenna destroying it in the past but the glass didnt explode. Maybe because he uses heavy thick glass jars I dont know. I'm sure if lightning was strong enough it would turn a jar into a grenade but I would be more concerned about my house burning down from such a hit! |
Capt205
Junior Member
Username: Capt205
Post Number: 22
Registered: 5-2005
| | Posted on Thursday, July 21, 2005 - 1:29 pm: |
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For now, I unscrew the coax and hang it off the desk. I like the poly phaser idea, I'll have to get one of those. Using rg213, which I was told is good coax, and even with the amp, I am having no rf problems with anything in my house or the neighbors. Antenna is 120' away from the house. Trying to protect against or avoid a lightning strike. |
Hollowpoint445
Advanced Member
Username: Hollowpoint445
Post Number: 573
Registered: 6-2004
| | Posted on Thursday, July 21, 2005 - 6:09 pm: |
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Tech237 - How and where would a ground loop be created? My understanding of ground loops is that they are caused by unintentional ground paths causing equipment to misbehave. This would be an intentional ground path, and on the same conductor. Where would it loop to?
Perhaps if the equipment ground was not as good as the coax ground the coax would effectively become the equipment ground, but that wouldn't cause a ground loop if the station were constructed with a single point ground where both the equipment ground and coax ground would be joined - right before they enter the home.
Hotwire - Grounding doesn't improve performance. If anything it might reduce RFI caused by near-field radiation, but that's not an increase in performance, it's a decrease in interference.
Glass is not a good insulator for static electricity. Rub glass with fur or a soft fabric and watch the static electricity build up! The glass jar method was always poor. If you want to do something with your coax connector do something constructive. Connect a panel mount SO-239 to your grounding system and screw it into that connector during storms.
The ARRL has lots of good information about lightning protection here:
http://www.arrl.org/tis/info/grounding.html
http://www.arrl.org/tis/info/HTML/grounding/index.html
http://www.arrl.org/tis/info/lightning.html
|
Tech237
Moderator
Username: Tech237
Post Number: 167
Registered: 4-2004
| | Posted on Friday, July 22, 2005 - 9:05 am: |
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Hollowpoint,
With the right setup you can show that a voltage potential can exist between two supposedly ground points. And you are right, if it is a single groundpoint no loop can exist, and that is why I said do not ground the coax at both the tower and where it enters the house.That is no longer a single groundpoint.
I am trying to recall what book it was (Univeristy textbook) that demonstrated the point about voltages between two grounded points but at the moment I cannot. I did demonstrate the effect to one class i taught by having them stand on a boatslip rail, in ankle deep water and then touch a copper rod in the ground about 2 foot away. The voltage was small (less than 1 v) but none the less it was there. |
Tech833
Moderator
Username: Tech833
Post Number: 1030
Registered: 8-2002
| | Posted on Friday, July 22, 2005 - 10:02 am: |
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I may not be the almighty ARRL, but I do play a broadcast engineer on radio and TV. I have said this before, and it looks like the time to say it again is here.
Do you guys know how all those professional repeaters and radios high up on those mountains keep on working for years and years through one lightning storm after another and never get damaged? Do you think that someone runs up to the mountain EVERY time there is going to be lightning and disconnects all the coaxes and puts them in glass jars? Do you think all the radios go off the air every time there is a storm (because the coaxes are sitting in jars)? NO! I'll tell you how all those professional, police, fire, broadcast and other radios stay on the air- Polyphasers!
And the best part? Polyphasers aren't JUST for the pros, thanks to Copper Electronics, the same technology available to the pros is available to you too.
When installed properly, a Polyphaser will also take care of your station grounding question. Yes, the radio should be grounded (bonded) to the other equipment inside the shack, and all that equipment should be grounded as well. The Polyphaser installs just outside your shack (or alternately, inside right where your coax enters) and then is grounded as close to it as possible with a ground rod. That rod should be bonded to the system ground.
The way a Polyphaser works, if you use an ohm meter and measure through it from center conductor to center conductor, it will show OPEN. That's right, the Polyphaser isolates your equipment from your antenna. There is NO connection from your antenna to your equipment! However, the Polyphaser does allow RF to travel through it, so your radio and antenna do not even know it is there. The loss is about the same as the connectors alone, and will not ever be noticed, not even with the most sensitive test gear. Anyway, if lightning does happen to come down the center of your coax, it is shunted to ground through a special gas filled shorting device that has multiple strike capability. Since the equipment is isolated, the equipment would not even 'see' the strike. The radios would not know the antenna had been hit! They will just keep on working like always. You can even be on the air during the strike!
I own a couple repeaters on hilltops that get hit all the time. They stay right on the air through the whole thing. No big deal. Of course, your antenna might get blown apart (you have no control over that anyway), but your radios will be safe.
So, do you really think you can be home to disconnect your coax and put it in that glass jar EVERY time lightning approaches? Do you really want to stay off the air every time lightning is around? Why not use a Polyphaser and forget about the voodoo glass jar idea and go have fun? |
Hollowpoint445
Advanced Member
Username: Hollowpoint445
Post Number: 577
Registered: 6-2004
| | Posted on Friday, July 22, 2005 - 4:33 pm: |
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Tech237 - The point of having multiple ground rods is to make the best possible ground. It might be that a single ground rod won't show a 0 volt potential due to the condition of the earth, moisture, etc. - but several ground rods would be closer. You have to look at the ground system as a whole, not as interconnected parts. As long as the currents are shunted to ground, it doesn't matter how much is done by individual rods in the system.
And as long as you only have one connection to the ground system, there won't be any loop. That's why it's called a SINGLE POINT GROUND SYSTEM. You connect your equipment to the ground system at a single point.
You point would be valid if you make more than one connection to the ground system, but if you make only a single connection you eliminate the ground loop potential. |
Slowhand
Junior Member
Username: Slowhand
Post Number: 29
Registered: 7-2005
| | Posted on Friday, July 22, 2005 - 6:30 pm: |
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Some things I've wondered about:
I have seen towers set upon insulators. A wire from the tower to a sparkplug screwed into the end of a grounded pipe.
The explanation I was given, was that this kept the tower from ground potential. In other words no place for the lightning to go. The sparkgap was just in case. It was a hefty path to gnd for the lightning, but still avoided putting the tower at ground potential. This was a ham array with several antennae. Would it be of value to cb use?
I'm no engineer, but on am commercial towers isn't that the purpose of the Johnny Balls ?
The "Johnny Balls" are set at a gap large enough so that the RF voltage on the tower cannot arc to ground, but lightning will jump the gap to ground .
Also I believe folks sometimes get electrical ground confused with rf ground plane. |
Bigbob
Senior Member
Username: Bigbob
Post Number: 2066
Registered: 12-2001
| | Posted on Friday, July 22, 2005 - 9:32 pm: |
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Once and for all,Tech 833,is it nessessary to have a tower or mast ground and a seperate ground for the poly-phazer or just one for the poly-phazer or is the tower ground needed to keep the concrete pad in one piece during a strike?Bigbob |
Tech833
Moderator
Username: Tech833
Post Number: 1034
Registered: 8-2002
| | Posted on Saturday, July 23, 2005 - 1:56 pm: |
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Slowhand-
Since the tower itself IS the antenna on an AM broadcast station, it needs to be ungrounded. it is RF fed usually at the base of the tower. The johnny balls are there to provide a low impedance path to ground when it gets hit. There are usually plenty of coils inside the AM tuning unit to reduce the current flowing to the transmitter. Also, you might notice a 'drain loop' in the connection between the tower base and the tuning unit. That is a high impedance path for lightning and encourages it to drain through the johnny balls to ground.
Bigbob-
Here you go, in plain English. Ground your antenna. Bond all your equipment together and to your Polyphaser. Ground your Polyphaser. Bond the seperate grounds together. |
Bigbob
Senior Member
Username: Bigbob
Post Number: 2070
Registered: 12-2001
| | Posted on Sunday, July 24, 2005 - 4:11 am: |
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Thank you,thank you,Tech 833.Got to get some 8 gage ground wire to bond grounds together,thanks a bunch .Bigbob |
Slowhand
Junior Member
Username: Slowhand
Post Number: 30
Registered: 7-2005
| | Posted on Sunday, July 24, 2005 - 10:11 am: |
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I see Tech 833, so it would be of little use for our purposes.
thanx! |
Tech833
Moderator
Username: Tech833
Post Number: 1035
Registered: 8-2002
| | Posted on Sunday, July 24, 2005 - 11:54 am: |
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Slowhand- It would be counterproductive to your purposes. UNLESS- You plan on loading up your tower/pole as the antenna itself. I did a 'stealth' installation once wher an 18 foot TV push-up pole was isolated and loded up at the base for 10m ham use. There was a small TV antenna on top (with the coax going through the middle of the mast for isolation) and the boom acted like the 'top hat' for the 5/8 wave radiator. The guy wires were not wire at all, but small black dacron marine line (it's only called 'rope' when it's not intended for boats).
Ground planes were 4 in number, small black wire, and sloped down the roof from the pole 'antenna' base. Tuning was accomplished by adjusting coil/cap in very small box at the base of the pole. The insulator was a glass power pole type painted flat black, and made to look like a standard TV pole roof base mount.
Worked great, nobody ever knew.... |
Slowhand
Junior Member
Username: Slowhand
Post Number: 32
Registered: 7-2005
| | Posted on Sunday, July 24, 2005 - 5:40 pm: |
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hehe thats cool ! |
Chainsawiowa
Junior Member
Username: Chainsawiowa
Post Number: 43
Registered: 1-2005
| | Posted on Sunday, July 24, 2005 - 7:26 pm: |
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You can spend all the money and hire a electrician to do your lightening defensive tricks, But LIGHTENING will go and travel anywhere it wants to !! |
Troublemaker
Intermediate Member
Username: Troublemaker
Post Number: 143
Registered: 2-2004
| | Posted on Sunday, July 24, 2005 - 10:02 pm: |
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according to Hal. oops,sorry Hal  |
Tech833
Moderator
Username: Tech833
Post Number: 1037
Registered: 8-2002
| | Posted on Monday, July 25, 2005 - 2:07 am: |
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Chainsawiowa wrote: "You can spend all the money and hire a electrician to do your lightening defensive tricks, But LIGHTENING will go and travel anywhere it wants to !!"
That is NOT true. You are very misinformed. There are no 'tricks', there are sound, proven engineering practices which will greatly reduce your chance of getting hit, and virtually eliminate your chance of equipment damage in case you do get hit.
You are obviously in disbelief, but if you did just a little bit of web research on the subject (NOT from CB related sites), then you will see that you are wrong.
Lightning (note correct spelling) is the completion of an electrical current flow. Since it is nothing more than electricity we are talking about, and electron current flow, we can direct and modify the current flow path any way we wish. Sure, lightning itself is unpredictable, but the path it takes once it reaches our protected systems is entirely predictable. |
Bigbob
Senior Member
Username: Bigbob
Post Number: 2075
Registered: 12-2001
| | Posted on Monday, July 25, 2005 - 5:11 am: |
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Even down or through wood and it'll turn dry sand into glass.Bigbob |
Wildrat
Intermediate Member
Username: Wildrat
Post Number: 197
Registered: 12-2003
| | Posted on Sunday, October 30, 2005 - 9:52 am: |
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Thank You 833, your explanation of the polyphaser in laymens terms really helped me understand what the polyphaser does. I have one now that will be used during the setup of my new station. I had never even heard of polyphaser till I came on this forum, and reading other threads on installations that are being done. I have found some copper strapping at Lowes with a clamp for the ground rod already on it. I am going to take more copper straps and make it thicker. The strap is about six inches long. So my polyphaser will be within just a few inches of the ground rod. I trust the technology, but I think I will disconnect my coax from the equip just to be safe the first couple of strikes. I live in Clearwater, Fl. The Tampa Bay area is suppose to be the lightning capitol of the world. I do not want to find out.
Wildrat |
Road_warrior
Advanced Member
Username: Road_warrior
Post Number: 888
Registered: 7-2004
| | Posted on Monday, October 31, 2005 - 9:15 am: |
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After reading Tech 833 posts and researching
the web on lightning protection, i'm actually
starting to understand this subject better.
The glass jar thing and just unhooking coax
from radio and laying it over something are
not good for ones health or property. |
Tech833
Moderator
Username: Tech833
Post Number: 1073
Registered: 8-2002
| | Posted on Monday, October 31, 2005 - 10:26 am: |
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Not to mention, are you sure you are going to be home and able to disconnect everything EVERY time a storm rolls in?
Isn't it MUCH more fun to stay on the air on those rainy nights talking with your buds? |
Wildrat
Intermediate Member
Username: Wildrat
Post Number: 205
Registered: 12-2003
| | Posted on Monday, October 31, 2005 - 12:42 pm: |
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Yep |
Crackshot
Junior Member
Username: Crackshot
Post Number: 44
Registered: 10-2005
| | Posted on Monday, October 31, 2005 - 2:01 pm: |
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Do these polyphasers mess up SWR, Receive or transmit using liners or barefoot? Any wattage loss? |
Sinker
Intermediate Member
Username: Sinker
Post Number: 202
Registered: 8-2005
| | Posted on Monday, October 31, 2005 - 8:04 pm: |
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I have NO PROBLEMS with mine and they give lots of PEACE OF MIND.....
Tim
CEF-634 |
Tech833
Moderator
Username: Tech833
Post Number: 1080
Registered: 8-2002
| | Posted on Sunday, November 06, 2005 - 12:50 pm: |
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They do not affect SWR. They do not introduce any loss. They will handle more than the legal limit on the ham bands. |
