Last Revision : 25 January 2008
My colleague and fellow ham Klaas Timm DL4LBK works with a very well performing four element yagi antenna on the 15m band (21 MHz). Now that the next solar maximum cycle is approaching we discussed the possibility of extending the already mounted antenna by some elements for the 10m band (28+ MHz). The tower and the rotator is not able to carry a multi-element antenna about half a wavelength above the existing antenna. So we had the idea of interlacing the elements for the higher band in between the elements of the 15m antenna.
In a first step all dimensions on the existing ZX 4 element 21 MHz antenna were measured and fed into EZNEC5+. This showed a well performing antenna for the 15m band. (See results below). Next step was to take the dimensions of an also existing 4 element (CB-radio 27 MHz) antenna and calculate its performance. The dimensions were slightly modified to achieve optimal performance on 28,3 MHz. BUT placing this design into the 15m antenna did not bother its performance ... The 10m antenna did NOT work at all. So elements were moved and lengths were carefully changed and quite a good performance was achieved. Gain and Font/Back-Ratio were not as good as done without the 15m elements around, but not very far away from this. The 15m antenna is affected only very little. An OWA (Optimized Wide-band Antenna) - as it can be found at W4RNL L.B.Cebik - has been tried to integrate, but this could not be get working properly.
The antenna is not realized yet. All material is available.
Get the NEC2 and EZNEC Simulation Files : DOWNLOAD HERE (ZIP)
3D Image of the extended ZX Yagi for 21 MHz
EZNEC 5+ Drawing of the extended antenna.
VSWR of the ZX "Original" 21 MHz section.
Freespace performance / Azimuth on 21 MHz
Freespace performance / Elevation on 21 MHz
Performance at 12m above ground on 21 MHz / Elevation
VSWR of the 28 MHz section.
Freespace performance / Azimuth on 28 MHz
Freespace performance / Elevation on 28 MHz
Performance at 12m above ground on 28 MHz / Elevation