W8JK
After my 4 elements periodic logarithmic beam has been destroyed, I was again looking for a directive antenna with a simple design that could allow a coverage of all bands from 20 to 10 m. I found in a French magazine (MEGAHERTZ N°96, Feb 1991, F9HJ, p91-95) an original article about the W8JK: it was an interesting design in the sense that all mechanical parts were connected together to the ground without any insulations between the elements and the boom.
As a reminder, a W8JK combines collinear in-phase elements with parallel out-of phase elements (four-element end-fire collinear array). This is a bidirectional antenna.
Antenna size
2 elements of 7.50 meters each
boom lenght : 3 meters
feedline: periodic array, then 450 parallel feedline and symetrical antenna tuner at the station
Results/Efficiency
With the help of the antenna tuner (McCoy type), the ROS was correct on all bands from 10 to 20 m (not a surprize !).
Directivity was hard to notice on 10 m, and was almost inexistant on all other bands. Obviously, I have been able to make contacts with this antenna, but it had never delivered what I was expecting in term of gain and directivity.
Overall, I have been disapointed with this antenna. Maybe the design was not correct and the same type of antenna with the two elements isolated from the boom and separated in their middle to form 4 independant half-wave antennas on 10 m would have been more efficient. I was to the point to test this design (I aalready had modified one element in that way) when my good friend Eric brought back to my home an old Mosley TH33JR. Few days latter, the W8JK was down to be replaced by the TH33JR ! Not to blame this type of antenna but I don't think I will ever try this design again as I believe that it can be efficient only on one band and not really usefull as a multiband antenna which is what I was primarily looking for.