Rabu, 04 April 2012

Antenna Modeling Links, Stealth Antennas, LPCAD, APRS, Cycling and Huskers

NEC/MININEC-based Software Vendors:

Other MOM-based Software Providers:

FEA-based Software Vendors:

  • HFSS 3D Antenna Structure Simulator

Antenna Structural Analysis Software:

NEC/MININEC Organizations and Resources:

Other RF and Antenna Software

Learn How Antennas Work!

Linear Dipole - set length to 0.5 (half-wavelength dipole) and notice that the impedance is near 73 ohms.  Radiation pattern shown is typical figure-8 pattern. When a half-wave dipole is close to ground, the impedance is lowered to near 50 ohms.  Thus a perfect match to 50 ohm cable.
-set length to 1.27 wavelength.  This is called an Extended Double Zepp antenna and produces the maximum gain possible from a simple center-fed dipole.  Notice that the radiation resistance (impedance) is about 90 ohms.  This antenna can be matched to 50 ohms by using a series inductor. Half of this antenna is 5/8 wave and is a common length for 2m mobile antennas. The 5/8 wave antenna is typically fed against a ground plane (car roof) and is usually matched with a tapped inductor.
-set length of dipole to multiples of 1/4 wave on each side (e.g. 0.5, 1.5, 2.5, etc.).  Notice how these lengths produce an radiation resistance (impedance) close to 100 ohms.  The patterns of these are made up of many lobes (cloverleaf pattern).

How do antennas produce gain?

Lincoln Amateur Radio Club Antenna Class

Links to Software and other information

LPCAD - Log Periodic CAD

NEC Model Library

The following files and links point to NEC/AO/YO models of various Ham antennas that I have simulated and/or tested over the past 30 years as an antenna designer. The NEC files may be used with any of the NEC-2 or NEC-4 programs such as 4NEC2, GNEC or cocoaNEC, however some of them with tapered elements may only be simulated accurately by NEC-4 or other MININEC-based software. These models will indicate in the CM lines if they need to use NEC-4 or 4NEC2. These models have varying degrees of accuracy. Some may be very close to actual performance. Others may only be an estimate. They are for you, as the experimenter, to use and improve.  This list will grow as I check each file before uploading, so check back often. Have fun!


VHF NEC Models:

  • 28DX  a 13.4 dBi low backlobe Yagi for 144.2 on a 12' 6" boom
  • 215DX a 16.35 dBi low backlobe high-performance Yagi for 144.2 MHz (metric dimensions)
  • 216CP  (AO file) a very experimental RHCP 2m beam with 12.3 dBic gain and single point feed
  • 216CP (NEC file) - updated 2-4-06 - improved axial ratio & VSWR
  • 23DF a 3 element Yagi for 2m Foxhunting (7.7 dBi & 40 dB F/B)
  • 25FB a 5 element 4' 4" boom Yagi for 2m Foxhunting  (9.4 dBi & 34 dB F/B)
  • 26FB  a 6 element 6' 6" boom Yagi for 2m Foxhunting  (10.4 dBi & 34 dB F/B)
  • 27FB  a 7 element 8' 6" boom Yagi for 2m Foxhunting  (11 dBi & 36 dB F/B)
  • 6m_3el_yagi  an 8.1 dBi low backlobe Yagi for 50.1 on a 6' boom
  • 6m_4el_yagi  a 9.8 dBi Yagi for 50.1 on a 12' 6" boom (use in 4NEC2)
  • 6m_moxon a 6.2 dBi "Moxon rectangle" for 50.1 MHz
The VHF antennas shown above include the "raw" element lengths.  That is, the element lengths are those used with a wood or plastic (dielectric) boom or supported above or below a metal boom with an large insulator. To convert these raw lengths into actual lengths used when passed through the center of metal booms, you need to add a correction factor, based on whether the element is insulated and passes through the center of a metal boom, or is shorted directly to the metal boom with a clamp.
If the element is insulated when it passes through the metal boom, the correction factor is approximately 1/4 the diameter of the boom.  For example, for a 36" (raw length) insulated element passed through the center of a 1" metal boom, the correction factor is 0.25", so the actual length should be 36.25" when built.

Stealth Antennas

This information on stealth antennas was presented at a Lincoln ARC meeting in March 2006.

Bike Helmet 2m Antenna Mount

How I mounted a 2m HT whip antenna to my bike helmet (or how to really look stupid on a bike)

Track WB0DGF on bike (last 48 hours)  Locate WB0DGF on bike (last known position)
Track WB0DGF in vehicle (last 48 hours)  Locate WB0DGF in vehicle (last known position)

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