I know that a jpole works without the need of radials. But, what happens if you add radials? Has that been modeled? Never considered it until today really. Would it pull the radiation angle down lower? Would it balance the field plot? Would it make your signal shoot straight into space and call in the alien invasion? Cut down on noise? Improve receiver noise? Or nothing at all. Yes it’s a vhf/uhf jpole.
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Jpole radials
- Thread starter nfsus
- Start date
They will do nothing to improve the signal and may in fact detune the antenna.
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So just where would radials attach to a J-pole?
Not seeing it.
73
Not seeing it.
73
If I was a radial, I’d guess at the base of the antenna. Not being a smart ass. My jpole has a flat base. It does not have the typical long downward leg. Think like an arrow antenna where it has the two elements extending off the base upward
The base of every 1/4 wave ground plane antenna is a high current point, and yet they have radials that work. Ground mounted multiband HF vertical ham antennas perform as electrical 1/4 waves and are literally mounted at ground level yet radials vastly improve the performance. Just saying.
Yes, a ground plane antenna has a low feed-point impedance because it is fed at a current loop, and that's because the antenna is a 1/4 wave length, or some odd multiple of 1/4 wave length.
A J-pole is an end-fed 1/2 wave length antenna, making its input impedance and its radiation resistance, very high, but to make it work with 50 Ohm coax, it's fed by a 1/4 wave, balanced feedline which acts as a transformer of 50 Ohms to approximately 2500+ Ohms needed to feed the end of a 1/2 wave antenna.
The problem with any 1/4 wave/ground plane antenna mounted near the ground, is that the current loop (where most of the antenna's energy is coming from), is at ground level, and coupling to the ground plane and Earth in many places except rocky and desert areas; that, with a low radiation resistance, makes any ground-mounted ground plane antenna, fairly inefficient. A half wave antenna places the current loop away from the feed-point, and further away from the ground if the antenna is near the ground, and it doesn't need any ground plane for impedance purposes, further lowering ground losses.
Can inefficient antennas transmit and receive? Absolutely!
A J-pole is an end-fed 1/2 wave length antenna, making its input impedance and its radiation resistance, very high, but to make it work with 50 Ohm coax, it's fed by a 1/4 wave, balanced feedline which acts as a transformer of 50 Ohms to approximately 2500+ Ohms needed to feed the end of a 1/2 wave antenna.
The problem with any 1/4 wave/ground plane antenna mounted near the ground, is that the current loop (where most of the antenna's energy is coming from), is at ground level, and coupling to the ground plane and Earth in many places except rocky and desert areas; that, with a low radiation resistance, makes any ground-mounted ground plane antenna, fairly inefficient. A half wave antenna places the current loop away from the feed-point, and further away from the ground if the antenna is near the ground, and it doesn't need any ground plane for impedance purposes, further lowering ground losses.
Can inefficient antennas transmit and receive? Absolutely!