|Details||2-El.-4m-Yagi||3-El.-4m-Yagi||4-El.-4m-Yagi (12.5+50 Ohm)|
|5-El.-4m-Yagi (28+50 Ohm)||6-El.-4m-Yagi||7-El.-4m-Yagi||9-El.-4m-Yagi|
70Mhz-Yagis by DK7ZB
The picture shows the 5-El.-70MHz-Yagi (28 Ohms) built by Adam, 9A4QV
Above the 5-Ele. is a 6-El.-28Ohm-Yagi for 2m.
Picture was taken during RSGB-CW-Contest in JN74BX
In some countries now the 70MHz-Band is available (unfortunatly in Germany I see no chance in the near future!) and I got several questions for scaling my 50MHz-Yagis for the 70MHz-Band.
The scaling was made with "YO", then I have smoothed the dimensions (fractals of mm are not a trustworthy thing!) and corrected, if necessary. The designs were proved with "EZNEC+4".
The elements are of 10mm- or 12mm-Aluminium, the boom should not be greater than 25x25mm (square) or 35mm (round), they should be mounted with small or without clamps above (!) the boom. It is no insulation necessary. Thick clamps need an additional correction factor (shorter elements). For the construction details see the 50MHz-Yagi-pages. If you use 10mm-Alu, correct the directors each 10mm longer, the reflector 2mm and the radiator 6mm (only 28-Ohm-types).
The Yagis have 12,5-Ohm resistance (use the DK7ZB-match with 2xlambda/4 50Ohm coax) or 28-Ohm (use the DK7ZB-match with 2xlambda/4 75Ohm coax). For 50 Ohm use a simple coax-choke.
Important notice: I have not built up the antennas, but I can guarantee that the antennas will work, hi... The only additional work you should do is to tune the length of the radiator, in practice the SWR should be better 1,2 at 70,2 MHz.
If you have any additional comments or photos for my homepage, send me an e-mail! All interested amateurs could have an advantage by that.
The plots show (from left to right) azimuth, elevation at 70,2MHz and SWR.
You can download the EZNEC-Files for own works and changes: DOWNLOAD