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End-fed verticals and Ground Planes
- Thread starter Marconi
- Start date
FREECELL
how do you isolate your antennas from the mast. i have thought of several ways to do that. but want to hear how you do it and some pictures would be nice if you have them.
aslo do you still ground the mast after insulatingit from the system or what.
thanks in advance.
how do you isolate your antennas from the mast. i have thought of several ways to do that. but want to hear how you do it and some pictures would be nice if you have them.
aslo do you still ground the mast after insulatingit from the system or what.
thanks in advance.
welp i figured out how to isolate the imax mount from the mast,(havent dont that yet) and i grounded the mast it self with a 10 foot copper rod and a piece of tinned copper ground strap. they were out of stock on the choke balun so i'm waiting on the next shipment. when that comes in i will take the antenna down to isolate and remount the antenna to the mast, and install the choke balun.
they said about 2 to 3 weeks tops. on the balun. then i can do some tests on this theory and let everyone klnow the results.
allthough even if this does or doesnt work after the extra $,time,and haslle from nieghbors.
i could have just goten a I10k for just a about 100 more shipped, and not had all this expierimenting to do LOL
Has anyone here put a mfj-259 on an imax ???? if you did what were the readings you got.
they said about 2 to 3 weeks tops. on the balun. then i can do some tests on this theory and let everyone klnow the results.
allthough even if this does or doesnt work after the extra $,time,and haslle from nieghbors.
i could have just goten a I10k for just a about 100 more shipped, and not had all this expierimenting to do LOLHas anyone here put a mfj-259 on an imax ???? if you did what were the readings you got.
"The choke-type balun is sometimes referred to as a current balun since it has the hybrid properties of a tightly coupled transmission-line transformer (with a 1:1 transformation ratio) and a coil. The transmission-line transformer forces the current to be equal, and the coil portion chokes off common-mode currents."
Ed Gilbert K2SQ and Frank Witt AI1H, contributors to the ARRL Antenna Book 20th Edition 26-22.
I would normally never challenge you freecell, but you have made quite a widely disputed claim. I am not trying to sound sarcastic, but is there something you meant that I am missing?
a simple coaxial choke is not a balun because of extremely poor SHIELD ISOLATION. since this is lacking there is minimal balanced to unbalanced transformation taking place, only a "partial choking" of the common mode currents on the outer shield, and not enough of that. the input and output ground connections need to be isolated for the balanced to unbalanced transformation to take place. this isn't happening in a coaxial choke. this is also why most baluns are housed in non metallic enclosures so that the input and output grounds at the SO-239 connectors have no path between them. to do otherwise would negate the "balanced to unbalanced" transformation effect. note the term hybrid....possessing some properties of each but not all the properties of both. in any event a coaxial choke is woefully inadequate at performing the necessary functions when compared to a commercial balun wound on a proper toroid form with the necessary isolation between the input and the output of the balun with reference to the enclosure used. the w2au baluns are a joke as well because of the poor insulation properties of pvc in this particular application. the properties of an air-wound choke in this respect compared to those of a balun wound on a material such as ferrite or similar material (for obvious reasons) are greatly lacking in performing the task supposedly being attributed to them. this is not so much a matter of balun or not balun as it is a matter of how much or how little. the degree to which any of these are operating as a balun or not is primarily a function of the value of the high impedance being imposed upon the outer shield of the transmission line in the case of coaxial feedlines. the higher the impedance imposed the more completely the common mode currents are suppressed or eliminated and the more pronounced the balanced to unbalanced transformation taking place
and like i mentioned elsewhere in the forum, unless you're using an antenna in conjunction with a radial system don't even bother with a balun of any type whatsoever as this would be counter productive. if you choke the common mode current flowing on the outer shield of the feedline it has to go somewhere and where you want that current present is in the elements of the elevated radial system itself. this is exactly why many have added radial kits to these popular antennas and have noticed no discernible difference in performance, because there is NO CURRENT flowing in the radial system. instead it is present in the support structure and the outer shield of the feedline, from the antenna all the way down the line to the rig. these antennas without a radial system are unbalanced for the most part, once the radial system is added they are more balanced than unbalanced in nature. add the balun and force the current back into the radial system and then you'll take notice. a dipole (balanced antenna) operates the way it does because of the existence of opposing charges in both "poles". the manufacturers have assigned the job of the "other half" to the feedline and structure in lieu of the proper counterpoise and offered it as an option. make sure you know and understand the difference.
the magnitude of the ensuing electric and magnetic fields of the radiated electromagnetic wave once the transmitter is energized is directly proportional to the ability to achieve a balance of current/s in both the radiator and the radial system. for example, with 100W into a 50 ohm load the voltage present at the feedpoint will be approximately 70.7V @ 1.414A of current. (P = I squared X Z) under ideal conditions in a balanced antenna .707A of that current should exist in the main radiator and the other .707A should be more or less evenly divided among the elements in the elevated radial system. then you'll notice a difference.
the magnitude of the ensuing electric and magnetic fields of the radiated electromagnetic wave once the transmitter is energized is directly proportional to the ability to achieve a balance of current/s in both the radiator and the radial system. for example, with 100W into a 50 ohm load the voltage present at the feedpoint will be approximately 70.7V @ 1.414A of current. (P = I squared X Z) under ideal conditions in a balanced antenna .707A of that current should exist in the main radiator and the other .707A should be more or less evenly divided among the elements in the elevated radial system. then you'll notice a difference.
Thanks FC for the details. Can I assume that we should expect that if these currents are not stopped on the vertical feed line or supporting mast of a horizontal beam that we are also showering the field with vertical radiation about equal to the horizontal radiation on both transmit and receive? Talk about a loss in polar rejection between vertical and horizontal. That surely couldn't be good. Dare I ask where these currents would then go with a yagi beam setup as it has no Ground Plane and does a gamma deal with this situation as some have noted.
I use to notice my Field Strength meters showing motion when keying up certain antennas I had up. I started watching that and trying to figure out why and what that was. Then common mode currents came to my attention. Before I understood these currents even just a little bit, I thought I could whip the problem just by placing my feed lines on the ground as it exited the area at the base of the antenna on the way to the station. But, one day I dropped my line well to the ground during such a test with a buddy and he told me that amazingly he noticed a little drop in my signal to his station nearby. That sure got my attention, because I would have thought it would maybe make some increase as I solved the problem of line radiation, but nope! I no longer showed any FS activity at my radio, but my signal dropped off some and that was not what was supposed to happen, so I believe. I knew then that all that I was doing was forcing some on my signal available to radiate, straight into the earth, never to be radiated into the airways. That is when I first started thinking about what was really going on and how to deal with it.
FC, your words on this topic and others has been most helpful in my understanding even when I don't understand everything. I wish to thank you for your presence here on WWRF.
I use to notice my Field Strength meters showing motion when keying up certain antennas I had up. I started watching that and trying to figure out why and what that was. Then common mode currents came to my attention. Before I understood these currents even just a little bit, I thought I could whip the problem just by placing my feed lines on the ground as it exited the area at the base of the antenna on the way to the station. But, one day I dropped my line well to the ground during such a test with a buddy and he told me that amazingly he noticed a little drop in my signal to his station nearby. That sure got my attention, because I would have thought it would maybe make some increase as I solved the problem of line radiation, but nope! I no longer showed any FS activity at my radio, but my signal dropped off some and that was not what was supposed to happen, so I believe. I knew then that all that I was doing was forcing some on my signal available to radiate, straight into the earth, never to be radiated into the airways. That is when I first started thinking about what was really going on and how to deal with it.
FC, your words on this topic and others has been most helpful in my understanding even when I don't understand everything. I wish to thank you for your presence here on WWRF.
Fl Native asks;
I bought a brand new Imax in May of 2004. Right out of the box I installed it at 20' to the base so I could reach everything.
Using my Autek Analyzer and my Daiwa Cn-801, here are some iterations I made in readings that I got moving the rings around. I did not double check anything, I just recorded the data gained and analyzed things later. I use my Kenwood TS-570D to fed it thru the Daiwa at 10, 20, and 100 watts and of course use the Autek direct to the TX/RX end of my regular and random feed line. I did no check at any different heights in this effort.
Daiwa showed best resonance at SWR=1.01 @ 27.700 mHz
Autek showed X=0, R=51, SWR=1.02 at 27.880 mkz.
Lowered the rings one full turn.
Daiwa showed resonance at 27.500 as one might expect.
Autek showed X=0, R=49, SWR=1.03 at 27.900 mHz. This was not what I expected.
Lowered rings to the bottom
Daiwa showed the following 1.65 SWR @ 25.000 mHz and 1.7 SWR @ 28.500 mHz.
Autek showed X=+8, R=49, SWR=1.20 @ 27.600
The frequency did not go down much considering I lowered the rings all the way down.
Something happened at that point in my work and I did not continue the effort.
Conclusions are that this was all at one height and maybe that height was not a good height, thus my resonance was higher than expected. The Imax matcher somehow manages to control the match extremely well in all iterations in test, so I assume that because that is done the antenna manifest some strong losses in order for that to happen. This is probably substantiated by the fact that it is so broad banded also. The Imax generates just about as much RF from the feed line as it does from the radiator and I don't think that is too good either. This is not a conclusion however, it is fact, this thing is terribly noisy all the time.
One day I will try this again at maybe 36-40 feet. Maybe things will be better, but I don't believe anything will help this one from having very strong common mode currents all the way down the feed line.
Oh Yeah, BTW. I have one on a 10' mast and I talked to the UK the other day here from the Gulf Coast of Texas, so they do talk. Didn't want to make this too bad of a report.
I bought a brand new Imax in May of 2004. Right out of the box I installed it at 20' to the base so I could reach everything.
Using my Autek Analyzer and my Daiwa Cn-801, here are some iterations I made in readings that I got moving the rings around. I did not double check anything, I just recorded the data gained and analyzed things later. I use my Kenwood TS-570D to fed it thru the Daiwa at 10, 20, and 100 watts and of course use the Autek direct to the TX/RX end of my regular and random feed line. I did no check at any different heights in this effort.
Daiwa showed best resonance at SWR=1.01 @ 27.700 mHz
Autek showed X=0, R=51, SWR=1.02 at 27.880 mkz.
Lowered the rings one full turn.
Daiwa showed resonance at 27.500 as one might expect.
Autek showed X=0, R=49, SWR=1.03 at 27.900 mHz. This was not what I expected.
Lowered rings to the bottom
Daiwa showed the following 1.65 SWR @ 25.000 mHz and 1.7 SWR @ 28.500 mHz.
Autek showed X=+8, R=49, SWR=1.20 @ 27.600
The frequency did not go down much considering I lowered the rings all the way down.
Something happened at that point in my work and I did not continue the effort.
Conclusions are that this was all at one height and maybe that height was not a good height, thus my resonance was higher than expected. The Imax matcher somehow manages to control the match extremely well in all iterations in test, so I assume that because that is done the antenna manifest some strong losses in order for that to happen. This is probably substantiated by the fact that it is so broad banded also. The Imax generates just about as much RF from the feed line as it does from the radiator and I don't think that is too good either. This is not a conclusion however, it is fact, this thing is terribly noisy all the time.
One day I will try this again at maybe 36-40 feet. Maybe things will be better, but I don't believe anything will help this one from having very strong common mode currents all the way down the feed line.
Oh Yeah, BTW. I have one on a 10' mast and I talked to the UK the other day here from the Gulf Coast of Texas, so they do talk. Didn't want to make this too bad of a report.