March 2005 Round this time I upgraded the LF transmitter PA to a design improvement published by Jim Moritz - M0BMU for the G0MRF 300 watt class D LF transmitter. This changed the PA stage from voltage mode to current mode. This improvement gave a substantial increase of DC input power to about 600 watts with much lower PA temperature. Up to now I have successfully tested the new design into a dummy load on the bench to 600 watts and into the antenna on air to 400 watts. A useful addition to LF test gear was the “LF Antenna Ground Loss Bridge” built from ideas and notes by Alan Melia (G3NYK), Johan Bodin (SM6LKN) & Lloyd Butler (VK5BR). The Marathon Tx VFO & case was recycled to become this 136 khz antenna ground loss bridge, click the document icon on the right for details of my trials and tribulations (requires Adobe Reader). Also thanks to Alan for the additional help and feedback during this project.
December 2005 Time has passed quickly and any antenna work has been on hold whilst I get some operating time and personal time in. I have recently purchased a Yaesu FT-847 in view of consolidating all my HF, VHF and UHF transceivers (including add-ons and peripherals like keyer & speech processor etc) into one box, I am really delighted with the rig and its features.
The big problem resulting from this was the change to the antenna set-up on my mast to re-mount my rotator and various beams but to my disappointment was not able to install a decent LF antenna as it would foul the rotating beams.
January 2005 During the severe gales we usually experience at this time of the year the Spiral Top MK 2 antenna suffered a setback in such that the high winds snapped the fibreglass stub mast between the upper and lower spirals thus rendering the assembly unusable. The stub mast has unfortunately been shortened but strengthened and a Spiral Top Load Mk 3 was created. The Mk 3 was similar to the Mk 2 but using only one section with the spiral wound over and under the PVC spreaders, this suffered arcing damage with the higher level of RF and was removed. I have now reverted to a version of the Umbrella top load until such time that I could continue with my antenna experiments.