Longwire or Dipole? - Reasons to choose.
Posted: Fri Nov 04, 2022 11:50 am
Well, is there a difference, and if there is , by how much? Does it matter.
If you've already decided to just string up a wire and see it it works, you're wasting your time here; we're after real and practical answers to this very practical question.
Wires are cheap compared with tower-mounted beams, and very much easier to make inconspicuous to the delight of families, not to mention your friendly HOA. Ok, you're broke, have space and decide to proceed with a wire antenna.
Does end-fed or center or off-center-fed work best, and by how much? If you cant't quantify something, you're not in a position to offer an opinion worth anything, so here goes:
First, is some kind of dipole or end-fed better? Ok, now with that sorted out, EZnec or similar can show that generally the impedance should rise as the feedpoint of an OCFD is moved towards the ends, but really? How much? Here are some measurements that maybe you can repeat in your own backyard: https://www.hamradio.me/antennas/electr ... ation.html
So what to make of it? Feedpoints anywhere can work, with suitable matching. IMHO, that is the key: if you want a multiband antenna, with similar impedances for all ham bands, it may be best to avoid feedpoints at half- aquarter- etc wave multiples, so choose something like 20% rather than 25% (quarter), or 17% (eighth). FWIW, a 20% feedpoint works well for me.
If you've already decided to just string up a wire and see it it works, you're wasting your time here; we're after real and practical answers to this very practical question.
Wires are cheap compared with tower-mounted beams, and very much easier to make inconspicuous to the delight of families, not to mention your friendly HOA. Ok, you're broke, have space and decide to proceed with a wire antenna.
Does end-fed or center or off-center-fed work best, and by how much? If you cant't quantify something, you're not in a position to offer an opinion worth anything, so here goes:
First, is some kind of dipole or end-fed better? Ok, now with that sorted out, EZnec or similar can show that generally the impedance should rise as the feedpoint of an OCFD is moved towards the ends, but really? How much? Here are some measurements that maybe you can repeat in your own backyard: https://www.hamradio.me/antennas/electr ... ation.html
So what to make of it? Feedpoints anywhere can work, with suitable matching. IMHO, that is the key: if you want a multiband antenna, with similar impedances for all ham bands, it may be best to avoid feedpoints at half- aquarter- etc wave multiples, so choose something like 20% rather than 25% (quarter), or 17% (eighth). FWIW, a 20% feedpoint works well for me.