18 October 2003By NNN0JQH1 Wide Band Folded Dipoles A comparison between Wide Band Folded Dipole (WBFD) and an Open Wire Fed Dipole (OWFD)

18 October 2003By NNN0JQH2 Introduction Finding suitable H.F. antennas with wide bandwidths or having enough individual antennas to cover the spectrum piece by piece with good efficiency is a challenge. There has been interest in Wide Band Folded Dipoles (WBFD’s) as a possible solution.

18 October 2003By NNN0JQH3 Claimed Advantages of WBFD’s Low SWR (<2:1) over their specified operating range Since they are folded they are approximately one half the length of a regular 1/2 wave dipole

18 October 2003By NNN0JQH4 Sources Most of the data was taken from two articles by L.B Cebik W4RNL who is the author of the ARRL Antenna Modeling Course. They can be viewed in their entirety at and The ARRL Handbook and Antenna Manuals

18 October 2003By NNN0JQH5 Test Conditions WBFD and OWFD of equal overall length (90 ft) WBFD design frequency 2-30 MHz OWFD fed with open wire from a tuner Equal height

18 October 2003By NNN0JQH6 Problems Common to Both SWR varies cyclically in relation to the antennas length vs. the frequency in wavelengths. At frequency increase and the antenna becomes greater than 1.25 wavelengths long it develops lobes. The lobes have nulls that can be dB deep. At 25 MHz there are 8 lobes. Height above ground affects both equally.

18 October 2003By NNN0JQH7 WBFD Considerations Wire spacing has little effect comparing 8 and 16 inch SWR for an antenna at 20 feet typically between 1.2 and 2.2 (lower will be higher) Should be within the tuning range of modern transceivers Certainly in the range of external tuners

18 October 2003By NNN0JQH8 OWFD Considerations For all band operation must be fed with open wire feed from an antenna tuner Has greater than 5 dB gain over the WBFD over the entire frequency range Lighter weight and no twisting problems

18 October 2003By NNN0JQH9 WBFD Issues The “matching resistor” satisfies the transmitter as far as SWR but does nothing to change the fact there are very high SWR’s on the antenna and therefore high currents and voltages. The resistor absorbs this “reflected” power at a cost of 50-90% converted to heat.

18 October 2003By NNN0JQH10 WBFD (continued) WBFD has a knee in the gain curve that falls off dramatically below 7 MHz. The knee can be moved lower by lengthening the antenna. This worsens the problem of lobes at higher frequencies.

18 October 2003By NNN0JQH11 OWFD In the OWFD/tuner combination reflected power is kept on the antenna and only the losses are the resistive losses of the wire Most of the power is radiated

18 October 2003By NNN0JQH12 The Numbers 5 MHz WBFD 7 dB below the OWFD 4 MHz WBFD 10 dB below the OWFD 3 MHz WBFD 15 dB below the OWFD 2 MHz WBFD 24 dB below the OWFD These are significant values with a negative effect on communications capability

18 October 2003By NNN0JQH13 2 MHz on-the-air Tests Comparing full length 160 meter dipole at 65 feet, 90 foot WBFD and full length 80 meter dipoles at 25 feet Logged listening tests on stations across SNE for several weeks Compared to the 160 meter dipole the WBFD was down 5 S-units. The 80 meter dipole was down 4 S-units

18 October 2003By NNN0JQH14 On-the-air Test (Continued) In terms of SWR the WBFD was “matched” to the transceiver. The 80 meter dipole was not. Inserting a matching circuit between the 80 meter dipole and the transceiver would recover much of the lost signal making it several S-units better than the WBFD

18 October 2003By NNN0JQH15 Wrap Up If you want to be on the low bands and circumstances require a minimum length antenna an OWFD will give you better performance. If frequency hopping is required and a tuner won’t work for you a WBFD may work with the understanding that the performance is much poorer.