I will check the bug in simulation, but meanwhile as far as I know, the 1/2 wavelength mono-pole with ground-plane is equivalent of a full-wave dipole, not that of a half-wave dipole.
Removed the bug in simulation. Here are results.
Please note that these simulations are for antenna in free space. When I find time, I will simulate for antenna at 6 meters (20 feet) above real ground, and post results.
(1) Spider 1/4 wavelength Whip
Geometry: Whip = 68 mm, Radials = 8 x 68 mm, slanting 45 deg, Built on connector SO239
Gain = 1.31 dBi
Impedance = 66.1 + j 24.7
SWR 50 = 1.66
. (2) Spider 1/2 wavelength Whip
Geometry: Whip = 138 mm, Radials = 8 x 68 mm, slanting 45 deg, Built on connector SO239
Gain = 0 dBi
Impedance = 511 - j 722
SWR 50 = 30.7
.
(1) Horizontal Ground-plane 1/2 wavelength Whip
Geometry: Whip = 138 mm, Radials = 8 x 68 mm, Horizontal, Built on connector SO239
Gain = 3.5 dBi
Impedance = 833 - j 658
SWR 50 = 27.1
. SIMULATION 1 OF 3: Spider, 1/4 wavelength Whip CLICK ON IMAGE TO SEE FULL SIZE IMAGE
Thanks for running the simulations and explaining why a 1/2 ground is a bad idea. I like the look of the py4zbz it looks like it could be made from ridged rod and be very stable. Thanks again @abcd567
I used the core of some cellphone coaxial cable I had handy. About 4mm diameter. SO239 soldered directly to the matching section. The ‘chocolate block’ connectors were to allow quick changes to the antenna length.
The principle and probably sole advantage of the 1/4 wave GP (or its ‘cantenna’ variants) antenna for home builders, is that it is the easiest to replicate and thus get an effective result.
Spider and Cantenna are naturally tuned for 50 ohm / 75 ohm system, and have lot of dimensional tolerance. These two characteristics makes them ideal DIY by a novice.
Thanks for posting your tests. I’m curious…looking at the photos of the J-pole I see what looks like fiberglass cloth near the coax feed point. Why is that there? Tnx.
OK…I’ve never seen material like that in the coax I use, rg-8/58/174 coax…but have seen foil used along with braid. I don’t know what the other types have under the jacket…unless it’s the shield…maybe the lighting or angle of the photo makes it look like fiberglass cloth… anyway, hope his experiments continue. I enjoy seeing what others are building.
Hello, @wiedehopf@wa4chq You are correct - the connections to the “j” are very close together and the glass fiber tape was simple insulation. (its the tape we wrap arround the conductors in super conducting magnets) Stay safe this year ATB