Loading the tower for 160m - The crossed booms of the yagis act as a capacity load increasing the equivalent electrical length up to aprox. 110º. The elements of the yagis are isolated from the boom so they do not add much to the capacity load. Some W’s hams have reported arcing between the elements and the boom in similar systems when running high power. I have not noticed any problem of this nature when TXing at full power, perhaps their concept of “high power” is a little bit different to mine. Top height of the system is 28.4 meters The tap of the gamma match is at 14 meters high. Separation from the tower is 1 meter. Shunt cable is copper wire with a diameter of 2.5 mm. The 2:1 SWR bandwidth of the antenna could be increased by adding 2 more spaced wires to build a wire cage for the gamma. No need for that as our permitted bandwith in EA in 160m is just 20 KHz :( At 4 meters high are located the 1/4 wave radials and the coax feed with its capacitor to the gamma match. At this height all the coax cable braids coming down from the tower (7 in total) are connected to the tower (ground potential) and to the antenna switch SixPak The bottom of the tower is properly grounded through several surrounding copper rods. This is for safety and lighting reasons and cannot be considered a sufficient ground for RF purposes. RF return currents through the ground would suffer great losses if the elevated resonant radials were not installed. In theory, the feed point of the tower (4 meters high) and the bottom should be at the same RF potential (RF mass). However it would be a good idea to install a detuning cell to keep the RF currents in the tower below the radials at a minimum and to force that all return currents are located on the radials and not in the lossy terrain The coax feed lines from the SixPak, the rotor cable and all control cables are coiled to form a choke before entering into the shack to avoid RF currents. The capacitor of the gamma match is made of 4 strips of coax cable RG213 of 98cm each attached together in paralel. Total capacity is aprox 410 pF and it is adjusted to minimum SWR by the simple method of cutting its length. Home        Shack       Antennas       Maritime Mobile       Propagation        Gallery          QSL info