Antenna Design

• Antennas by N6LF Rudy Severns
• Insulated Wire and Antennas (PDF) by Rudy Severns N6LF. Conclusion: Substantial impact on Ground Plane Verticals with sparse radial systems. These problems tend to go away as the radial count is increased to twelve or more for elevated radials and 16-20 for ground surface or buried radials. Otherwise, leaving the insulation on the wire is pretty benign and loss due to the insulation, either new or old, does not seem to be significant.
• The 468 Factor
• Antenna Theory
• Antenna 101 by Ward Silver N0AX
• Of Fields and Feedpoints
• Ladder Line and a Ladder Line Calculator
• NVISAntennas -- Understanding Amateur Radio NVIS Antennas and Propagation
• An-Ten-Ten-nas by LB Cebik W4RNL PDF
• Dual Inverted V Dipoles as a DX antenna
• Flag antennas
• Joe Hallas, W1ZR, presentation A Comparative Look at Multiband Antennas PDF. Upshot: consider the non-resonant balanced line tuner-feed dipole
• Practical Antennas PDF
• Receivers, Antennas, and Signals from MIT Open CourseWare
• MMANA-GAL Windows and Basic based antenna-analyzing tool based on the moment method
• OCFW Off Center Full Wave antenna
• Quad Antennas in QEX Part 3, Part 4
• Royal Signals Amateur Radio Society antenna pages
• Simple Ham Radio Antennas series first antennatuners, without tuners part 1, part 2, part 3, and part 4
• Windom antenna by K4ABT
• Wire Arrays for DX'ing
• G5RV vs ZS6BKW vs Fan Dipole vs DX-CC vs Trap Dipole YouTube video lecture
  • G5RV: SWR in the range of 5:1, must be used with an antenna tuner, significant feed line losses. NOT a QRP antenna. Gain ~6dB.
  • ZS6BKW: computer optimized G5RV changing only the dimensions and ladder line impedance. Can be configured, by trimming the ladder line and antenna wire, for less than 2:1 SWR simultaneously on 40, 20, 17, 12, and 10M. Does not provide close in comms. Gain ~9dB. Overall, hard to beat given the simplicity and performance.
  • Fan Dipole 80/40/20M less than 2:1 SWR if you have the space and trim it properly. Gain ~12dB.
  • Alpha-Delta DX-CC less than 2:1 SWR on 40, 20, and 15M. Does not provide close in comms. Cost ~$150.
  • Trap dipole: narrow bandwidth forces one to use a tuner.
• Folded Skeleton Sleeve Antennas
  • A Folded Skeleton Sleeve Dipole for 40 and 20 Meters QST May 2011 pages 58ff
  • The Folded Skeleton Sleeve on Other Ham Bands QST October 2011 page 48 and supplement
  • 6 + 2 = 1 A Folded Skeleton Sleeve for 6 and 2 Meters QST October 2012 page 49
  • An Easy to Make Two Band HF Ground Plane QST December 2013 pages 35ff
  • Easy Two-Band Ground Plane for Other Band Combinations QST March 2015 pages 41ff

Antenna Design Details

• To Balun or Not (PDF) ... MUST install a current balun, otherwise the feed line will radiate up to ~35% of the energy.
• Dipole based upon AA5TAB's article on 2018-07-12 last updated November 04, 2009
  • For an inexpensive, low profile, high performance antenna the dipole antenna simply can't be beat.
  • A dipole is an antenna that is a resonant 1/2 wave in length.
  • A dipole can be fed with RF energy anywhere along its length although center feed is the most common followed by end feed (see below).
  • They are independant of ground by nature and therefore require NO ground to properly function as an antenna.
  • If fed in the center, no matching network is usually needed since the impedance is very close to that of standard 50 ohm coaxial cable although the impedance does very slighty with the height above the ground.
  • Length (feet) = 490 / Frequency (MHz). For 20m, use 33 feet. For 40m, use 65.5 feet. NOT including the length required to attach to the center and end insulators.
• End Fed Half Wave based upon AA5TAB's article on 2018-07-12 last updated October 11, 2014
  • In practice the impedance at the end of an end fed half wavelength antenna is on the order of 1800 to 5000 ohms.
  • HF is where this type of antenna is most practical.
  • For permanent home use you may also want to try a conventional L-network consisting of an inductor in series and a capacitor to ground on the antenna side. The L-network does not offer the feedline isolation that a link coupled tuned network does but it does offer a larger bandwidth for a given setting.
  • Typically, a parallel tuned circuit is used at the end of the antenna with the feed line link coupled or tapped to the coil in the circuit.
  • The 0.05 wavelength "counterpoise" length is what I also determined empirically as to being the ideal length for the counterpoise.
  • Coupler turns ratio of 8:1 provides the most stable SWR versus "counterpoise" length.
  • According to Moxon (HF Antennas for All Locations, L.A. Moxon, RSGB, 1990, pgs. 43,46), because of the very high impedance (i.e., very low current) at the end of a half wavelength antenna, only a small counterpoise (1m @ 14 MHz) or a few pF of capacitance to ground is required to return the current.
  • Therefore, for a link coupled antenna provide a 0.05 wavelength counterpoise and length the end fed antenna by 0.05 wavelength.
  • For an antenna where the feedline may not be totally isolated is to use a resonant half wave length antenna adjusted to provide a resistive load to the coupler.
  • Any deviation from the resonant antenna length will require a similar increase in "counterpoise" requirement.
  • Only when the "counterpoise" (and/or feed line common mode path) becomes near a half wave length itself will the return currents equal that of the antenna.
  • How to Make An End Fed Half Wave Antenna Work
  • QRPGuys Portable No Tune End Fed Half Wave Antenna has the tuned circuit on the rig side of the coupler, not the antenna side.
• Random Length Wire based upon an anonymous webpage at the University of Delaware.

1. use a single antenna with a tuner
2. use an antenna with multiple harmonic resonances that fall close enough to bands of interest
3. use an antenna that has separate tuning adjustments for each band
4. use a truly broad-band antenna that covers a wide spectrum
5. use resistive loading to reduce the SWR by absorbing power

The second would include loops, G5RV, OCFDs, etc. where the wire and feedline lengths are chosen for reasonable performance across multiple bands. This often works well on some bands, but none of the ones I know of will give a low SWR on all of them.

The third would include multiple dipoles on a common feedpoint, trap dipoles or beams, multiple quad loops on the same set of spreaders, etc. Generally this allows individual adjustment for each band rather than relying on the harmonic resonances in the wire.

The fourth isn't as common in ham use, but has increased potential with the addition of the WARC bands. This would include log-periodic arrays, true fan dipoles, discones, conical monipoles, and even some HF quadrifiliar helix arrays that are much more common in military or commercial service. These might operate, for example, from 5 to 30 MHz with an SWR under 2.5 : 1. They tend to be more complex to build, but certainly are capable of what you are looking for.

The fifth includes antennas such as the T2FD or other broadband folded dipole designs with a large resistor in the middle, as well as some of the newer "dummy load on a stick" versions. It IS possible to make a plausibly efficient antenna like this that covers multiple bands, but most common designs achieve low SWR at the expense of signal strength.

Note that you can also have combinations of these methods in a single antenna.