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End-fed verticals and Ground Planes
- Thread starter Marconi
- Start date
The cure for common mode problems caused by less-than-perfect grounds is inserting a 1:1 choke balun in the system at the antenna feedpoint. The coax should also be kept away from the radials as it exits the area of the radials and the antenna. An antenna with a poor ground using few radials cannot have a support mast grounded to the radial common point (at least it shouldn't if designed properly). There is no exception to this!
if you would like a definition of "less than perfect ground" let me know.
if you would like a definition of "less than perfect ground" let me know.
OK, so we can either fix the ground radials to make them good, probably by adding more, and add a choke balun at the feed point to fix the problem.
Or, we can leave the ground radials like they are, add a balun, and insulate the mast from the common point of the radials.
I guess it is obvious that since the 11 meter antennas we all talk about here are not setup like suggested, then they must have common mode currents on the feed line. What is a sure way of telling or testing the system, so one can check it after making such changes?
Assume I'm from Missouri.
Or, we can leave the ground radials like they are, add a balun, and insulate the mast from the common point of the radials.
I guess it is obvious that since the 11 meter antennas we all talk about here are not setup like suggested, then they must have common mode currents on the feed line. What is a sure way of telling or testing the system, so one can check it after making such changes?
Assume I'm from Missouri.
by measuring either the presence or absence of current on the outside of the shield using a current ammeter probe.
so if you don't have have a rf ammeter how code you check for common mode current? or what would the "symptoms" be. also an ant. like the cushcraft ar-10 would not be good huh?
so from what is here im guessing to get the full advantage of a ground plane kit on my imax i need one of these palomar-engineers.com/Balun_Kits/balun_kits.html
?????
?????
That is pretty much the way I see it Native. Then if the GPK does its job, you should be good to go.
Rfoverlord, this does not mean that these antennas are no good. I have a Ringo that is hard to tune and changes tune if you move it a foot, up or down, but works like a champ as far as signal goes to some local locations.
By stopping the errant currents, and providing a good raised ground path, maybe you will eliminate some possible losses due to the currents that would otherwise get into the earth, plus it hopefully will improve the signal and its strength into a pattern more close to the horizon by not skewing the radiated pattern of the vertical or beam, plus maybe it might reduce local TVI potential in the neighborhood. If it does any or all of this, it sounds like a plus for me even with the trouble it takes.
But that they work in spite of these approaches is a testament to how easy we have it in our hobby.
Its sort of like tuning your auto and keeping your tires inflated well, it will probably get by even if you don't do it.
Rfoverlord, this does not mean that these antennas are no good. I have a Ringo that is hard to tune and changes tune if you move it a foot, up or down, but works like a champ as far as signal goes to some local locations.
By stopping the errant currents, and providing a good raised ground path, maybe you will eliminate some possible losses due to the currents that would otherwise get into the earth, plus it hopefully will improve the signal and its strength into a pattern more close to the horizon by not skewing the radiated pattern of the vertical or beam, plus maybe it might reduce local TVI potential in the neighborhood. If it does any or all of this, it sounds like a plus for me even with the trouble it takes.
But that they work in spite of these approaches is a testament to how easy we have it in our hobby.
Its sort of like tuning your auto and keeping your tires inflated well, it will probably get by even if you don't do it.
the use of the ferrite beads as suggested by palomar engineers do not provide a high enough impedance to eliminate common-mode currents and are inferior to a properly wound balun on a toroid form. the beads also saturate easily at moderate power levels.
in reference to another popular balun under the W2DU monicker which are housed in PVC, these also don't get the job done because PVC is usually contaminated with trace amounts of copper, carbon black and other materials with poor dielectric properties, literally dissipating as much as 20% of the power applied at hf frequencies.
both are poor choices.
in reference to another popular balun under the W2DU monicker which are housed in PVC, these also don't get the job done because PVC is usually contaminated with trace amounts of copper, carbon black and other materials with poor dielectric properties, literally dissipating as much as 20% of the power applied at hf frequencies.
both are poor choices.