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Chad
Advanced Member
Username: Chad
Post Number: 577
Registered: 11-2004
| | Posted on Friday, November 18, 2005 - 11:38 am: | 
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This topic is spawned by requests that we discuss the thread in my member's section in this section. I will post my original text wiht links to the pics in the pics section of this forum. I will also copy questions and responses thus far. Moving it here will keep the pic section from being overpopulated wiht discussion.
Bear wiht me, there may be a linking mistake but I'll do my best 
Some pics of my "Ugly Balun"
I felt I needed a balun on my Imax 2000. I have always had feedline radiation problems and RF in the shack regardless of mondo grounding, etc. As you can see in earlier pics I have some test gear in there and much of it is sensitive to stray RF. Although I do not key up and take measurements at the same time I do want it out of the shack. This RF was also causing me to have problems with my bench power supply driving the radios as the RF on ground was affecting the over current protection on my Accopian supply. After the installation of the BalUn there is no RF in the shack and the Accopian will drive any radio and the amp with no problems whereas it had problems driving a Magnum 257 alone. I also see no bouncy needles on the test gear and no RF is visible on the scope whereas it used to just PEG the AC voltmeter from stray RF.
I went from a link on a website for the design but modified it with a couple things in mind.
1. I could not use existing coax, it was already there so i had to make connections as opposed to just wrapping existing coax around a former. It also had to "drop right in place" with little modification to existing equipment.
2. The connections had to be protected from the weather, it gets stupid in Illinois weather wise and I wanted the device to be as reliable as possible.
3. I wanted it away from the mast for vibration purposes and lack of close induction from loop to loop.
So here's what I came up with...
I measured out that the coil of 20' of Belden RG8X would take up 5" coiled around 3" PVC. I cut a 9" section to accommodate the coil and end caps. I drilled holed into the former at a steep angle to pass the coax inside the pipe without crimping or stressing it. I then drilled 2 holes on the leading edge to accommodate zip ties to hold the coax in place. this was sealed with hot-melt glue as seen in this pic of Coax entry detail.
http://www.copperelectronics.com/cgi-bin/discus4/board-auth.cgi?file=/77380/85473.jpg&type=image/jpeg
I affixed the top cap and sealed it off, the bottom cap would contain a whip of Davis RF Bury-Flex and a female 239 connector so that the Imax can be disconnected and this unit dropped in place. Here are the internal connections.
http://www.copperelectronics.com/cgi-bin/discus4/board-auth.cgi?file=/77380/85474.jpg&type=image/jpeg
http://www.copperelectronics.com/cgi-bin/discus4/board-auth.cgi?file=/77380/85475.jpg&type=image/jpeg
The 239 was then screwed down and the connections were fully potted with hot melt glue. After this the end cap was sealed up. This would now look quite questionable in a carry-on bag in an international airport! see:
http://www.copperelectronics.com/cgi-bin/discus4/board-auth.cgi?file=/77380/85476.jpg&type=image/jpeg
I decided that since the end caps were round that it would make a perfect pathway for water to run down into my connections. I cut a section of the same PVC and used it as a collar on the bottom of the cap. this would make a "drip ring" to at least keep water from RUNNING all over the connections. I don't care if they get wet, just not under constant soaking. Here are the connections with the ring attached.
http://www.copperelectronics.com/cgi-bin/discus4/board-auth.cgi?file=/77380/85477.jpg&type=image/jpeg
http://www.copperelectronics.com/cgi-bin/discus4/board-auth.cgi?file=/77380/85478.jpg&type=image/jpeg
The ring was affixed with PVC adhesive and further potted with, you guessed it, Hot glue. I found my stash of glue sticks after the move
To keep the BalUn off of the mast i decided to mount it on stand off's using smaller PVC pipe. The smaller Sched 40 was cut to length and rounded into a concave shape to facilitate mounting to the end caps and the mast. It was not an act of precision as it was done on a bench grinder. Notches were made in the PVC to bring hose clamps through to attach it to the BalUn assembly and to the mast as can be seen in the finished pics in the shop:
http://www.copperelectronics.com/cgi-bin/discus4/board-auth.cgi?file=/77380/85479.jpg&type=image/jpeg
http://www.copperelectronics.com/cgi-bin/discus4/board-auth.cgi?file=/77380/85480.jpg&type=image/jpeg
So it's done, total cost was less than 10 bucks because I had to buy a female 239 connector and some caps. The rest was just lying around the house. The build went quick and it IS tested to be completely submersible
Of course no job is finished until the product is put into use, so without further a-do I went to climbing and installed it that evening. As you can see in the pic it was dark, but it's up and works well. So there you go
http://www.copperelectronics.com/cgi-bin/discus4/board-auth.cgi?file=/77380/85481.jpg&type=image/jpeg
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This was posted by Marconi:
Chad looks neat to me, but here are some suggestions and questions to consider for discussion at least.
Why didn't you just use two SO-239's in the bottom cap and use a jumper up to the antenna with the feed line going to the other connector? Just so you wouldn't have that 213 pig-tail hanging out there that could work the glue loose waving in the wind? If you had two SO-239's in there, you wouldn’t have to patch the two different coaxes together either. You know that when the center conductor leaves the confines of the shield, RF starts to happen on whatever conductive it is hooked to. That would seem to me to kind of defeat the purpose.
There is also an issue of having this kind of balun very close to the feed point of the antenna. With this pig-tail or the jumper being maybe 3' long you still have a line to radiate before the high impedance point at the balun starts to cancel the common mode currents flowing out of the feed point. Doesn't that still leave you some disruptive RF at the feed point?
I noticed that you do not have a ground plan kit attached to the antenna. Arguably this antenna normally uses the feed line as a counterpoise and we both feel that is not good. That is why you built the balun. But, what do you have now that provides the necessary ground path that the antenna is going to need, and is still looking for? It is either going to use the coax, the mast, or a counterpoise if available to provide the 2nd pole of the antenna.
I have probably gone on too much already, so I'm going to post. To bad I can't edit any mistakes I might have made here, but that is the way it goes.
Chad, your presentation is great and I encourage your efforts. I don’t wish to knock your plan and product, but how say you to these points?
Marconi
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I replied:
Marconi, Here's a couple answers, hope they make sense
Why not 2 connectors? One less for corrosion later down the road. That glue ain't going anywhere, the bottom of the cap is completely potted in adhesive. Sorry i did not get a pic of that, sometimes I get things sealed up and think "darn I forgot to snap a shot!"
As for the patch, the center conductor is soldered and heatshrinked, the shields are twisted and connected, care was taken to make sure they run as parallel to the center conductor and spaced with glue, this was then wrapped in aluminum tape and shrinked over the entire patch making sure the aluminum is attached to the shield conductor.
The site I was looking at for the design had the balun AS the feed point, as for the jumper radiating... I would rather have 2-3 feet radiating than the whole feedline. My main concern was with RF in the shack and it's associated problems with test/audio equipment. that problem has been ratified.
It looks like it's using the mast as the counterpoise now The farther locals (about 50-60 miles) are not noticing any decrease in signal strength. No skip lately though to give it the royal test.
The actual ground plane kit is coming when the new tower goes up. As luck would have it I found one the day the ground froze solid! Probably next spring now as the soil here is quite dynamic this time of year.
I appreciate your comments. Actually it was a way to kill some time in the shop and get my head off other projects for an evening. I DO like not having RF in the shack! That was driving me nuts regardless of the grounding schemes I was using, it was always there. Now there's none other than what's coming from the antenna, the coax is dead as a doornail as tested from a high impedance pick to the scope. Makes me feel a little safer too!
Chad
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Kid Vicious Worte:
very cool chad! did you ever get any difinitive answers about what diameter to use?
i was wondering why you put both connections on the same end until i saw the last pic and realized that the other way would get wet. i can see the reasoning behind using the jumper coming out of the bottom instead of using another SO-239; why put another connector inline and introduce the possibility or stray RF or insertion loss.
how did that coping on the bench grinder go? still have all your knuckle skin? Oh yeah, i think i am helping to keep the hot glue business in the black with the ammounts that i have used over the years.
i even made my own cordless hot glue gun for use on a set when i needed to make a quick repair and cant run a 500' cord.
i bought one of those car jump starters that you can recharge, and a small power inverter, and voila! instant hot glue that you can carry with you. i put it all in a box and hqave gotten many compliments on my little secret weapon!
later,
matt
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My reply to that is as follows:
I wad lead to believe that the diameter of the tubing is not as important as the length of the coax used. I went wiht 3" because I had it and felt that it MAY reduce wind loading a tad.
Bench grinder: Slow and steady wins the race the band cuts were made wiht a dremel and as you can see not exactly precice!
As for the portable hot glue gun: That my friend is a novel idea! Come up wiht a butane one like a Soldering Iron and you will be rich!
Chad
Remember all, Silence is golden, but, duct tape is silver |
Marconi
Intermediate Member
Username: Marconi
Post Number: 488
Registered: 11-2001
| | Posted on Friday, November 18, 2005 - 1:53 pm: |
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First off let me remind everyone that this is all about common mode currents on the feed line (CMC).
The Kid is next. OK! Kid, you know I’m always questioning you don’t you? Really it ain’t personal, it just appears that way. It is true that 239’s do have a smidgen of loss, but they are nowhere as likely to generate RF as will a coax patch. Chad noted later that he took care that the shield was made to completely surround the center conductor, trying to insure the proper relationships for the current path inside the coax, but even with the glue as a bridge and the foil to extend the shield completely around the center conductor, nobody could really know if the patch was RF leak proof or not. Most of us don't have a device to check this out.
At this point in the system, after the balun had done its work, you sure don’t want to create another RF feed point to start the CMC’s flowing again. So I suggested another SO-239 here, and if installed as well as Chad can no doubt do, that SO239/PL259 connector will not leak RF.
Even if the patch didn’t leak, a patch like that will most certainly create and impedance bump in the feed line, and that ain’t too good either. And, as I said before we know that if 239/259 fittings are installed well they will provide an almost flawless transfer of current across the connection.
Even with this said I would hold out an argument for not having a jumper at this point at all. I would connect the balun as directly to the feed point as possible. Even this small segment of coax line will likely radiate with CMC’s right at the feed point, before it gets to the high impedance condition we hope exist on the outside of the balun. This CMC(RF)can and will likely affect the radiation pattern of the antenna as length of the line here has little to do with the affect. This is the very reason why baluns are typically placed right at the feed point.
Chad admits that the antenna is probably now using the mast as the counterpoise, because there are no ground radials as yet installed to balance the currents in the radiator and provide the pole we want in the antenna and I agree. Since the feed line is adjacent and parallel to this mast, it would be very likely that those CMC’s will radiate right onto the feed line, so aren't we back to square one with CMC.
How could it work any other way if CMC’s are working anywhere below the feed point in this antenna even with the balun?
Just my thoughts.
Marconi
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Crackshot
Member
Username: Crackshot
Post Number: 72
Registered: 10-2005
| | Posted on Friday, November 18, 2005 - 2:13 pm: |
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Nice.Beautiful work. That is EXACTLY what I am thinking of doing this weekend with my dipole balun.
Think that idea wrapping coax around outside for my dipole balun? |
Chad
Advanced Member
Username: Chad
Post Number: 580
Registered: 11-2004
| | Posted on Friday, November 18, 2005 - 3:35 pm: |
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Unfortunately I do not have proper equipment to do impedance testing so testing the patch would be quite tough.
I also agree with Marconi on the negligible losses on coax connectors, but at the same time, what if there were two males and a barrel inside the housing, and the whip were for weather protection and aesthetics? Would the whip still be deemed a "problem child?"
Another reason I went with a whip is because the connection from RG8X to PL259 is crummy, tough to solder correctly and has great water entry potential. The buryflex and standard PL259 is MUCH easier to install and seems more solid in my eyes.
I have more PVC, I may try a 4" with one female at the bottom and a SHORT whip out the top. I will want to use RG213 though so I need to order some cable. this avoids my fear of RG8X connector "adaptors."
My next question comes with the addition of a GPK using the balun. The coax is still not an RF ground, the mast is, SOOOO where does the GPK derive the RF ground from? Is the mast still of some sort a counterpoise?, at this point I have no problem with the mast being ground as long it provides a GOOD RF ground.
I also at this point see no difference in RF in the shack from when the coax is dangling from the tower and firmly affixed. I DID check this before attaching the coax. But Heck, that may all change with the new tower.
I may build another just for grins, I need to get cable and I see nothing happening before early December due to some plans which I will disclose later
Another thing to keep in mind is that I am the true meaning of Amateur, freshman, greenhorn, etc! I ventured into this project with a chunk of PVC, 40' of RG8X, and talking on the Copper chat room. I am in no way saying that I have it all worked out, but I'm having fun learning while working it out
Chad
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Chad
Advanced Member
Username: Chad
Post Number: 581
Registered: 11-2004
| | Posted on Friday, November 18, 2005 - 3:51 pm: |
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Crackshot,
Watch this thread, there may be a revelation here Plans MAY change as information is combined.
Chad
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Marconi
Intermediate Member
Username: Marconi
Post Number: 489
Registered: 11-2001
| | Posted on Friday, November 18, 2005 - 6:36 pm: |
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Unfortunately I do not have proper equipment to do impedance testing so testing the patch would be quite tough.
I put that in there to remind us that such a patch is iffy. It is pretty obvious that you did not find you’re line to be a problem, because you said the reaction on installing the balun was unremarkable. I think you would have had a hint by match or SWR change if you had a bump. Maybe they come in degrees, but every time I see one made at manufacturing, it always was very obvious.
I also agree with Marconi on the negligible losses on coax connectors, but at the same time, what if there were two males and a barrel inside the housing, and the whip were for weather protection and aesthetics? Would the whip still be deemed a "problem child?"
If that were so, then maybe. I was just seeing both ends of the RG8x ending in a SO239, whether both are at the bottom or not. The coax feed line would attach to the output and the input would accept the jumper from the antenna. Or, better still the input at the top directly to the antenna using a double female or a very short jumper. These type end feds do pass water directly into the SO239 so waterproofing is required with all exposed connections of this sort. I have a sure cure for that one, it has never failed me.
Another reason I went with a whip is because the connection from RG8X to PL259 is crummy, tough to solder correctly and has great water entry potential. The buryflex and standard PL259 is MUCH easier to install and seems more solid in my eyes.
You are correct again and I’m sure you find attaching either coax to the SO239 much easier. There you can keep things really short and neat at the attachment point.
I have more PVC, I may try a 4" with one female at the bottom and a SHORT whip out the top. I will want to use RG213 though so I need to order some cable. this avoids my fear of RG8X connector "adaptors."
My next question comes with the addition of a GPK using the balun. The coax is still not an RF ground, the mast is, SOOOO where does the GPK derive the RF ground from? Is the mast still of some sort a counterpoise?, at this point I have no problem with the mast being ground as long it provides a GOOD RF ground.
Good question. If a good balun is installed and the GPK is attached to the Imax base mount which is at ground potential, then the radials being pretty much evenly spaced around the antenna near the feed point will hopefully share equally the current with the radiator. That is our goal. If this does not happen then certainly any difference in the currents being equal will appear as CMC on the mast. In this case a little current can still be a lot. This is what I feel you still have with just the balun installed.
The idea here is to create a high impedance condition with the balun at an area on the coax right at the feed point, so that the current will be forced to flow into the low impedance ground plane instead of on the outside of the low impedance coax or mast. If the radials are not there, or if they are not adequate for the purpose, or if there is extra line in a space between the feed point and the balun, then some of these currents can still spill over onto the mast and then onto the coax outer shield that is beyond the balun. No balun, no ground plane, then no decoupling of the coax from the antenna. This can even reduce the amount of current that gets to the radiator. The ideal condition is to have balance with equal currents spread out among the radials that sum to equal those currents in the radiating element.
I also at this point see no difference in RF in the shack from when the coax is dangling from the tower and firmly affixed. I DID check this before attaching the coax. But Heck, that may all change with the new tower.
How did you become aware that you had RF in your shack?
I may build another just for grins, I need to get cable and I see nothing happening before early December due to some plans which I will disclose later
Another thing to keep in mind is that I am the true meaning of Amateur, freshman, greenhorn, etc! I ventured into this project with a chunk of PVC, 40' of RG8X, and talking on the Copper chat room. I am in no way saying that I have it all worked out, but I'm having fun learning while working it out
What’ed he say?
Marconi |
Chad
Advanced Member
Username: Chad
Post Number: 582
Registered: 11-2004
| | Posted on Friday, November 18, 2005 - 7:13 pm: |
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"How did you become aware that you had RF in your shack?"
(C) Test equipment becoming VERY erratic. The needle on the AC voltmeter would just peg, as in you could hear it peg. The scope would lose sync, sometimes show an RF waveform if the sweep time was right. Freq counter going crazy.
Occasionally the computer would hiccup. Audio equipment would hum when the mic was keyed on AM and you could hear garble when speaking. On SSB the garble would sound more like voice. When testing digital gear with the lids off I would have problems with a noticible amount of error correction going on, sometimes causing audio quality problems. I had a problem with "mic bite" that was cured with more extensive grounding. While using a power supply to power the rig the power supply (Accopian) would go into over current protection, even with a barefoot Magnum 257. I now power wiht a battery and charger, but, switched to the Power supply with no problems. I still use the battery because I like the current reserves.
So, in my eyes I had a serious problem, even though I only use about 100-110W of power to "keep it clean".
With the GPK.... Where does the"summed current" go if the feedpoint RF ground is of high impedance?
Chad |
Marconi
Intermediate Member
Username: Marconi
Post Number: 490
Registered: 11-2001
| | Posted on Friday, November 18, 2005 - 8:25 pm: |
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The feedpoint RF ground is not at a high impedance, the outside of the shield on the balun is hopefully in a high impedance condition and the common current cannot pass, unless there is no ground plan available. If there is no ground plane then the current will flow down the mast. The current has to go somewhere, because it is looking for two poles to complete the circuit.
If the mast is insulated from the ground or the antenna then the CMC will flow right past the balun on the next thing connected to a ground, the coax. It will go to the earth like the balun was not even there, working or not.
This is probably a general view of things, but that is basically how I think about it. |
Chad
Advanced Member
Username: Chad
Post Number: 583
Registered: 11-2004
| | Posted on Friday, November 18, 2005 - 9:43 pm: |
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Got it, As I was walking away from the computer to watch a movie I also hit myself in the head and said... "DUH, I made a BALUN, A BALUN, Get it dummy? B-A-L-U-N, as in BAL-UN. Then it became clear Long week
I'm off to Rock-N-Roll for a couple days, I'll check back in on Sunday. Tomorrow if I get a chance, but probably will not have time to post.
Have a GREAT weekend!
Chad |
Marconi
Intermediate Member
Username: Marconi
Post Number: 491
Registered: 11-2001
| | Posted on Saturday, November 19, 2005 - 3:27 am: |
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Chad, I finally sat down and read the whole thread over. As I suspected I did make a few mis-q’s as we went along, so I have made some new conclusions about your idea and product.
You told me what caused you to notice the RF condition. After you installed the balun in line you noted a reduction or elimination of the bad responses. That cannot be denied. After thinking about this fact, I have come to a new conclusion about what might be going on in your case. What you have done with your Ugly Balun, is working as intended. That is what you wanted to accomplish. My thinking about the use of a balun and ground plan was taken from a different point of view, and I just now realized that. Maybe we can discuss this point of view in another thread on improving the efficiency of your antenna at a later date. I have been posting some about such things already. These are two different goals and there is nothing wrong with either, so I now concede that your idea works for the purpose you intended.
However, I have an idea you could try that may solve your problem without even the use of the balun. It is very simple, but it may not be as convenient. It will require you to have some of your coax lying on the earth or under the ground a bit since you have Davis cable. So, I would keep what you have installed. But, this idea is to simply add some additional coax to your line if necessary, and let the line drop to the ground under your antenna. Run the extra line all the way to the shack on the ground. Run as much on the ground as is available. Don’t allow any coax to hang out in the air or above the ground. Have as little as possible elevated. This space of coax along the ground will allow the earth to absorb the CMC currents, and you should see the RF in the shack reduced considerably. If that happens then it tells me that your balun is working to take the CMC of the feed line and that the CMC on the mast is not transferring back on to the line below the balun. This is good. Again that is exactly what you wanted to do.
I was my thinking from the beginning of this discussion that this CMC is wasted energy that could hopefully be radiated from the antenna. I think this is the nature of the Imax to have CMC, and maybe it occurs on many other end-fed verticals that we use in 11 meters as well. Let me know if you ever get a chance to test this idea and how it worked out.
Thanks for standing your ground on your issues so that I could finally see your point of view more clearly. This is why I said earlier "What'ed he say?" You’re no slouch.
Thanks for the discussion,
Marconi
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Sinker
Intermediate Member
Username: Sinker
Post Number: 251
Registered: 8-2005
| | Posted on Saturday, November 19, 2005 - 9:06 am: |
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Please forgive my inexperience to the point of even not understanding what the heck you are saying.
I have installed a tower where 1.5 feet of the legs are in the earth (for ground was my intention) then there is another 4 feet above that but below the grade line that is in concrete.
I have an 8' ground rod adjacent the tower that the antenna, tower and polyphasers are grounded to. This ground is also tied into the AC Ground.
I ended up with excess coax and was told to just wind it up at the bottom of the tower. It is LMR-400 so not real flexible.
Not exactly sure what a Balun does but sounds as though it should be a near the feed point as possible. Of course the excess coax I have is down about 40' from that point.
Should I wrap this coax around the tower tightly together like that Balun or should I just leave it coiled the way it is and resting inside the tower?
This may not even belong in this thread but I am wondering if I will gain anything by doing this with my excess coax.
Tim |
Sinker
Intermediate Member
Username: Sinker
Post Number: 252
Registered: 8-2005
| | Posted on Saturday, November 19, 2005 - 2:30 pm: |
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Wait - I guess wrapping it around my metal tower wouldn't be good huh?
Heck I don't know.... |
Starface
Intermediate Member
Username: Starface
Post Number: 325
Registered: 1-2005
| | Posted on Saturday, November 19, 2005 - 6:05 pm: |
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well Sinker you seen what I did with the extra coax, it went around the room behind everything..
Till next time
Starface CEF#476
Southeast Net Control
Auburndale,FL |
Road_warrior
Advanced Member
Username: Road_warrior
Post Number: 942
Registered: 7-2004
| | Posted on Saturday, November 19, 2005 - 7:30 pm: |
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My extra coax is strung around the cellar
then goes up through the floor to radio. |
Kid_vicious
Advanced Member
Username: Kid_vicious
Post Number: 859
Registered: 9-2004
| | Posted on Saturday, November 19, 2005 - 10:50 pm: |
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hey sinker, if you wanted to make yourself a "balun"
(do a google search on the word to learn more)
you need to install it at or very near the feedpoint of your antenna. i think its a worthwhile project, as it aids in preventing TVI. since you are using LMR400, you probably cant use the 3" PVC. you will need to find something more like 6"-8" pvc or something similar.
you dont need to be as elaborate as chad, but you will have to unhook your coax from the polyphaser first.
then, just wind the coax around the form, using your usual technical brilliance, and mount it securely in place. then just reconnect the coax.
should be fun!
marconi, i actually misunderstood your contention and therefore my response makes no sense.
i thought you were talking about using two SO-239's on the bottom of the balun resulting in TWO coax patches inside. again, i just misundrstood.
ALWAYS question me!
chad, can you direct me to where you got the info on the coax length and diameter? i gotta do some reading.
thanks,
matt |
Chad
Advanced Member
Username: Chad
Post Number: 588
Registered: 11-2004
| | Posted on Sunday, November 20, 2005 - 6:45 pm: |
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I have about 30' buried to the tower, it makes it "wife friendlier" I wiould not have purchased that cable if I did not have intention on burying it. This was before Copper sold the SIW buryable cable. Wasn't cheap but I got a lengthy remnant from Ebay.
Chad |
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