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Message |
    
Silverfox
New member
Username: Silverfox
Post Number: 9
Registered: 3-2006
| | Posted on Saturday, April 01, 2006 - 10:53 am: | 
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I read in a post here where someone said NOT to use gavanized pipe for an antenna mast...which is exactly what I was going to do. I planned on sinking the pipe into the ground and then bolting it to a concrete chiminey that goes up the side of the house. Is it true that I shouldn't use gavanized pipe? If so...why not??? Thanks.
silverfox |
Hatchet
Intermediate Member
Username: Hatchet
Post Number: 111
Registered: 7-2004
| | Posted on Saturday, April 01, 2006 - 11:42 am: |
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Galvanized pipe will work just fine. Just another CB myth. You may have to scrape or grind the galvanizing off to obtain a good ground. |
Wildrat
Advanced Member
Username: Wildrat
Post Number: 843
Registered: 12-2003
| | Posted on Saturday, April 01, 2006 - 12:29 pm: |
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If you could not use galvanized pipe, then people would have to take their towers down, their sliding poles, and various other components. Maybe they were speaking of not using galvanized ground rods. I use them also though. Copper, galvanized, it's all in the ground around here. |
Silverfox
Junior Member
Username: Silverfox
Post Number: 10
Registered: 3-2006
| | Posted on Saturday, April 01, 2006 - 12:39 pm: |
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Thanks, Hatchet...glad to hear that! Hey....do you mean just sand or scrape the pipe at the ground point? Surely, you don't mean the entire pipe....
Silverfox |
Road_warrior
Senior Member
Username: Road_warrior
Post Number: 1305
Registered: 7-2004
| | Posted on Saturday, April 01, 2006 - 1:03 pm: |
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Galvanized can be used as mast.
I wouldn't scrape off the Galvanized as it
will rust in those spots. |
Hollowpoint445
Senior Member
Username: Hollowpoint445
Post Number: 1149
Registered: 6-2004
| | Posted on Saturday, April 01, 2006 - 1:14 pm: |
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Don't scrape away the zinc - it's what makes it rust resistant. Aluminum ground wire, ground rods, and galvanized steel clamps used by TV antenna installers are are compatable. If you'd rather use something else I suggest you check out the galvanic index to find metals metals that work with zinc without promoting corrosion.
You may want to check your local codes about using galvanized ground rods because some folks here have said that they are not permitted in their area. |
Silverfox
Junior Member
Username: Silverfox
Post Number: 12
Registered: 3-2006
| | Posted on Saturday, April 01, 2006 - 2:48 pm: |
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oh-oh...here we go. So...there IS a problem with the galvanized pipe. I don't see why it would be such a bad thing to grind a small spot for the ground wire. So it rusts there after awhile. At least it's grounded. I really wanted to use copper for everything. How do you guys with the galvanized towers ground them?? And...what ELSE could I use to put up my Imax? I don't really need a tower with this high, concrete chimney going up the side of the house and some of those are galvanized anyway. I thought the galvanized pipe would be the easiest and cheapest way to go. The more I look into trying to do everything right with the installation of my system the more confused I get.
silverfox |
Marconi
Advanced Member
Username: Marconi
Post Number: 633
Registered: 11-2001
| | Posted on Saturday, April 01, 2006 - 3:07 pm: |
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I hear guys talking all the time about grounding their base antennas. It is as though they won't work without a ground if you read close or that the antenna will perform better, or it will stop TVI. I have messed with antennas all my adult life and I have never seen a earth ground have one iota of affect on a raised antenna. I mean zero.
What is it about the function of an antenna that is raised high above the earth that makes a ground necessary? What is it supposed to accomplish and how do you tell if it works as intended?
RF current has a natural tendency to flow towards the earth. If you improve the path for this current to flow to the earth what does that say about the RF you want radiated into the air or towards the horizon?
For me the idea is to isolate as much of the RF current at the antenna as possible (decouple) and make the RF radiate at that point (in the antenna) rather than try to get it to come to the ground below the antenna by lowering the resistance to ground as much as possible.
Isn't the low resistance in the outside shield of the coax low enough for you guys already. The problem is the feed line radiation and grounding the feed line 30' below at the earth seems to me to be trying to control the cat after it gets out of the bag. Believe me a 30' run of coax will radiate just like an antenna, but depending on the length it may not be radiating in some productive angle and for sure it will be radiating lower to the earth than the antenna. So as far as interference goes what does getting an antenna high do for us help us stop the antenna from getting into the neighbors stuff, all the while the feed line hanging below is doing a real good job of that just because you have encouraged a sufficient amount of available RF current to flow towards the earth below the antenna by lowering the resistance to earth as much as possible. I'm not even sure that you can successuflly to that even, but I will leave that to another argument.
If you provide a suitable and functioning Ground Plane to be raised up with your radiator then you are far less likely to have any significant RF flowing on the feed line that can cause local trouble, no matter how high you have the antenna and I believe you will actually be working on the right end of the radiator to solve a problem. For me it is like fixing a leaky hose, you stop the leak not help direct the water to earth.
Other than for safety reasons why should a Ground Plane antenna even need to be grounded at all? |
Road_warrior
Senior Member
Username: Road_warrior
Post Number: 1310
Registered: 7-2004
| | Posted on Saturday, April 01, 2006 - 10:45 pm: |
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Use Galvanized, Stainless Steel or Bronze
grounding clamps on Galvanized pipe.
There is no need to scrape off the zinc on
the pipe. |
Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 1365
Registered: 9-2004
| | Posted on Saturday, April 01, 2006 - 10:55 pm: |
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silverfox, you dont have to scrape the zinc off of the mast. use the clamps that are intended for this purpose like hollowpoint said.
matt |
Silverfox
Junior Member
Username: Silverfox
Post Number: 16
Registered: 3-2006
| | Posted on Sunday, April 02, 2006 - 10:55 am: |
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Well, well...an interesting theory for sure, Marconi. Although, with my small spattering of knowledge on the subjects of this hobby...I'm easily impressed. Your theory is the opposite of all that I have read on the subject of grounding radio systems but, to me at least, it makes sense. With this intuitive slant, you may also have answered my other posted question..."GPK or Not?" So...are you saying that your ant is NOT grounded? If not, you surely do ground the rest of your equipment in some fashion. How? I'm too inexperienced to go against all that I have read from the "experts" regarding the grounding of ALL equipment but you have tweaked my interest. At this shallow depth of my experience I don't believe I've ever seen or heard of anyone not grounding their ant.
silverfox |
Hollowpoint445
Senior Member
Username: Hollowpoint445
Post Number: 1153
Registered: 6-2004
| | Posted on Sunday, April 02, 2006 - 11:41 am: |
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YOU SHOULD ALWAYS GROUND FOR SAFETY! Grounding to prevent an RFI issue greatly depends on the issue you're having, and it probably won't help much.
Lightning is also an important consideration for grounding. If you live in an area where there is a possibility of a lightning strike then you should definitely do a safety ground at minimum. A more elaborate grounding system could even help to prevent damage to your equipment.
Grounding is one of those radio subjects that seems to elicit very different opinions. I prefer to rely on the information of professionals in the field rather than hobbiests. Several years ago there was a series of articles in an amateur radio magazine written by one of the folks at Polyphaser. It was written with amateur radio in mind, and was VERY informative. Polyphaser has some articles available on their website for download. Read them.
http://www.polyphaser.com/ppc_ptd_home.aspx |
Silverfox
Junior Member
Username: Silverfox
Post Number: 21
Registered: 3-2006
| | Posted on Sunday, April 02, 2006 - 1:14 pm: |
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Thanks again, Hollowpoint!! I will read with gusto! I guess I don't know the difference between grounding for safety and grounding for RFI. ??? Are you saying that grounding the ant is for RFI issues and grounding the mast is for lightening issues?? Shouldn't I do both? Sorry for being so uninformed.
silverfox |
Marconi
Advanced Member
Username: Marconi
Post Number: 635
Registered: 11-2001
| | Posted on Sunday, April 02, 2006 - 3:26 pm: |
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Well Silverfox, I can't totally isolate my antenna from the earth if for no other reason than the coax is attached. I do ground my radio system very well, again for safety reasons. I don't bother to try and insulate the mast or antenna in other ways except to try and improve on isolating the feed line from the antenna as best I can. Hopefully this effort will reduce the common mode currents (CMC) if they are flowing on the coax and induce them into the antenna where they can be radiated at a reasonable angle to do some real good. This will require a effective ground plane that is symmetrical, and one that provides enough mass and low resistance to induce the RF currents to flow int the GP system instead of on the outside of the feed line as is the case in the Imax, A99, and other similar antennas without suitable GP. I have even seen some ground planes that show excessive CMC if the GP is not effective or something else is wrong with the construction.
There is a way of insulating the supporting mast from the earth an still provide a suitable ground path at the base in case of lightning strikes. This idea uses a small air gap tap point to a good ground rod at the base. I have never done this, but it may prove to have some advantages if an antenna has a very effective ground plane system that can axcept all the available AC current in the coax and from the transmitter. I understand also that his arrangment helps eliminate ground loops that can sometimes occur in ground mounted verticals. This idea may provide improved radiating current into the part of the antenna up high that is radiating instead of on the feed line.
Simply providing a GP is not good enough though in order to stop CMC if they are present. Some sort of balun or choke is necessary to help discourage the passage of RF down the coax which is at a very low resistance potential. Typically the only way you can fix this is to create a very high impedance point in the feed line. This can be at or very near the feed point or at a voltage node 90 degrees beyond the feed point on the line. I have used a tuned 1/4 wave sleeve device to help me control CMC and it is very effective and does not exhibit saturation and overloading problems noted by other methods. I think I have pictures of this device on my pictures area on this forum.
Whatever device is used should tend to stop the current from flowing in the direction down the feed line to the earth and maybe even to the shack. It is however important to have an alternate path for these CMC to flow against.
Neither device alone will do the trick, the GPK will not do this alone, and the neither will the balun alone do this. One device alone will only force the currents to flow down either the supporting mast or the feed line. If you use a balun and it works, then the currents will flow on the mast and if it is connected to the earth via a DC ground then these currents are absorbed into the earth. This may appear to have made the currents stop and they have at the base of the antenna support. So they will not travel into the shack. Another dirty method of preventing CMC in the shack is to place the feed line on the ground from the base to the entrance to the shack. This allows the earth to absorb the currents in this span, but the feed line from the feed point to the ground is still radiating. Depending on how long this element (coax) is determines how well or not so well it radiates. None the less you still have RF radiating close to earth in this condition so that sort of defeats the purpose of raising the antenna high to help prevent local interference, right?
Now with all this said, I consider this only in theoretical terms, because I cannot prove that making any of these refinements really makes a practical difference in performance. In the Imax and the A99 I can see the affects of such changes reflected in the resulting bandwidth curves produced by the changes. And, the changes are substantial, so I can only assume that a resulting change in gain is also realized.
I associate increasing bandwidth with increasing losses and visa versa. Put another way, in order to improve gain in any antenna we must tend towards placing SWR in jeopardy (narrow bandedness). However, within the scope of both of these situations our radio is functioning at its peak, so from a human perspective it makes it difficult to tell improvements. This is similar to not being able to tell in actual communications whether a transmitting station is working at 1.0:1 or 2.0:1 SWR just by using your receiver in testing. Either you hear them or you don't, and this may not even manefest a difference at the fringes of communications either.
Are we not lucky that we do not have to have our two-way radio systems prefect in order to work at all? |
Silverfox
Junior Member
Username: Silverfox
Post Number: 23
Registered: 3-2006
| | Posted on Sunday, April 02, 2006 - 4:40 pm: |
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wow...thanks, Marconi. I was just told that I didn't NEED both the GPK AND the choke on my Imax 2000. I was told one or the other would suffice and I was going to opt for the GPK. Now you are telling me that BOTH should probably be used.....if I'm reading you right. I'm beginning to wonder if I will EVER get an ant up and get on the air with so much conflicting info. Like...my Imax hasn't arrived here yet and I would like to get the pipe for the mast. I was going to ask here what the inside diameter of the U bolts is so I could go ahead and get the pipe. But I found a thread where someone already asked that question and there were 2 answers. One from a Tech and one from someone that just got a new Imax. Guess what......the answers were two different sizes! The Tech said 1&3/4" pipe for the mast and the new owner of the Imax 2000 said 1&1/2". Go figure. I guess I can understand how so many theories can exist in this hobby....but hey....c'mon here....there should be only ONE correct measurement of the ID of the Imax 2000 U bolts! So....finding the thread did me no good....I still don't know the correct size pipe to get!??? Anyway....thanks for your long and detailed post, I appreciate it and will study it until I fully understand it all.
silverfox |
Road_warrior
Senior Member
Username: Road_warrior
Post Number: 1313
Registered: 7-2004
| | Posted on Sunday, April 02, 2006 - 8:54 pm: |
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Silverfox,
Are you going to run mast all the way to
the ground? Or just from the roof (chimney)
up? |
Silverfox
Junior Member
Username: Silverfox
Post Number: 24
Registered: 3-2006
| | Posted on Monday, April 03, 2006 - 8:03 am: |
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Road warrior...I will be going into the ground with the pipe as far as I can get in this rocky area and will use concrete around the base of it. Then I will bolt and/or strap it to the chimney. The chimney goes from under the ground up to about 20 feet or so...just over the roof top. I want to have the pipe go past the chimney about another 40 feet so I can mount my Imax 54 feet from the highest ground around the house.
silverfox |
Marconi
Advanced Member
Username: Marconi
Post Number: 636
Registered: 11-2001
| | Posted on Monday, April 03, 2006 - 10:18 am: |
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I understand you issues Silverfox. This is a reality in the Internet however. The correct working size of mast pipe for the Imax base is 1 -1/2" and no more.
I thought I qualified my remarks to say that my ideas here are theoritical in nature and that in actual practice not much real benefit or no is realized as human senses are able to perceive.
If you get the Imax, just put it together and get it up as high as your worries will allow. Then if you detect some RF getting back to your station you can always go out an put your coax on the ground where you can, from the base to the shack. This trick will not stop the CMC this antenna produces, but you won't be dealing with them at the radio. If you want the feed line to radiate into the air then just elevate the line where you can.
If you fixed everything required to stop these currents, you probably would be hard pressed to see the difference even though there will be differences. Most Imax operators probably don't even realize the Imax radiates from the feed line. |
Road_warrior
Senior Member
Username: Road_warrior
Post Number: 1315
Registered: 7-2004
| | Posted on Monday, April 03, 2006 - 2:59 pm: |
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Silverfox,
How do you plan on getting 54ft of heavy pipe and a 24ft Imax in the air???
Not to burst your bubble, but, that's a task.
Your better off mounting it lower for now and search for some used tower. Or do a tree mount, if you have a high enough tree. |
Silverfox
Junior Member
Username: Silverfox
Post Number: 26
Registered: 3-2006
| | Posted on Monday, April 03, 2006 - 7:19 pm: |
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I'll get it up, Road Warrior. Trust me.
silverfox |
Road_warrior
Senior Member
Username: Road_warrior
Post Number: 1316
Registered: 7-2004
| | Posted on Monday, April 03, 2006 - 8:38 pm: |
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OK....LOL |
Tech833
Moderator
Username: Tech833
Post Number: 1298
Registered: 8-2002
| | Posted on Tuesday, April 04, 2006 - 10:16 am: |
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I really wanted to stay out of this, however I think it is time to chime in.
First, bonding your antenna to your station is one of the most important safety measures you can take. Keeping ground potentials between antenna and radios will prevent the little zaps you get when connecting your antenna to the gear, and will also help prevent a direct lightning hit.
Second, using galvanized mast will hurt absolutely nothing. Almost all professional towers are galvanized. If you examine a professional installation, you will see 'ground kits' installed on the coax jackets either where they leave the tower or where they enter the building. This effectively grounds the antenna through the coax jacket with an ALL copper path.
Also, every tower is grounded for many reasons. Most of the time, grounded with multiple rods and sometimes with many radials too.
The idea is to dissipate lightning and static potentials as efficiently as possible, and also to provide the shortest, least resistance path to ground somewhere away from the radios. In order to keep lightning from heading down the coax cables to the radios, the system MUST be bonded together. That prevents the possibility of having a lower potential at the radio end, thus making the radios 'look' like a less resistance path than direct ground under the tower.
Marconi is approaching this from a different position, trying to reduce common mode currents. He is just doing it the wrong way. Common mode currents are not as dangerous as different potentials between radios and antenna supports. |
Silverfox
Junior Member
Username: Silverfox
Post Number: 30
Registered: 3-2006
| | Posted on Thursday, April 06, 2006 - 7:55 am: |
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Thanks 833. I had a long conference with a friend of mine just the other day who is a radio hobbyist and a self taught electrician. He agrees with you and I left his house finally understanding the grounding set up. It was really a great discussion with him drawing out diagrams and showing me things in his many catalogs. It all makes sense to me now. I have installed a new electric panel in the basement right under where my radio equipment will be and I think I will install a new outlet or two in my radio room to be dedicated only to that equipment. I did forget to ask him one question...if I have a dedicated outlet that will be grounded in the panel....could I run the ground connection from THAT to my mast ground or still do a ground rod outside the house right at the radio equipment and run a wire around the house to the mast ground? I'm not much good at understanding electrical systems so this may be another of my stupid ideas. Thanks.
silverfox |
Tech833
Moderator
Username: Tech833
Post Number: 1299
Registered: 8-2002
| | Posted on Thursday, April 06, 2006 - 2:31 pm: |
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Depending on your local electrical code, you may not be allowed to bond your electrical panel to your RF ground. However, from a safety and RF standpoint, it would be adviseable to have your electrical and RF grounds bonded. Mine are bonded by strap. |
Marconi
Advanced Member
Username: Marconi
Post Number: 638
Registered: 11-2001
| | Posted on Thursday, April 06, 2006 - 2:50 pm: |
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I was just trying to suggest that there are two aspects to grounding. Of course safety grounding is vital and the way 833 suggests is the only way to effectively ground. Trying to devise some method other than via the very low impedance in the coax is futil and you still have to disconnect in order to be fully protected.
Now if we are always lucky and the current is redirected as intended at the base of the antenna support into the earth, then will our equiptment be saved without a miracle.
Maybe grounding for safety has some performance benefits too, but I have just never been able to realize what they are in performance. I would be foolish to suggest that grounding is unnecessary, but I look at it from a purely safety issue and not performance. Now 833 will talk to us about the ground necessary for ground mounted commercial antennas, but I don't believe that is what these guys in 11 meters are looking to for advise.
I you want to impove something on your antenna then I don't believe earth grounding will fix that.
A very good thread and I learn things too you know. |
