VK5RMG work on 16/2/21

Summary of work completed at Bluff today as reported by Norbert VK5MQ:

  • Tested LDF4-50 feeder to new dipole antenna. Results were 20.8W into feeder at hut, 17.4W out at top of tower (into RF termination). Same result when connected to new dipole. So re-purposed feeder is OK. !?!
  • Tested VSWR at top of feeder into new dipole antenna, 1:1.5  . Had a long think and suspected 70MHz dipoles that were at roughly the same level and about a wavelength away. Ideally all dipole arrays/antennas should be vertically spaced to achieve adequate isolation and minimize interaction. OK, then swung the new dipole away from the 70MHz array, about 30 degrees to the west and VSWR came down to 1:1.25  . So that proved to me there was some reflection/interaction with the 70MHz dipoles. Now the new dipole points directly at the Mt Burr summit, so they still are basically oriented to the north.
  • Found that the phasing harness had one connector incorrectly assembled, with the N type centre pin protruding about 3-5mm proud of the connector. Repaired and tested harness at ground level with two RF terminations and again into one termination and one VHF dipole, VSWR 1:1.3
  • Installed second VHF dipole (resolved assembly issue) and phasing harness, VSWR at hut 1:1.03  !! Happy with that.
  • Replaced Naracoorte link feeder with known, good LDF4-50 heliax and routed onto cable clips and cable trays into hut. VSWR 1:1.5  and this is what I expected after appraising the condition of the link yagi. I think it’s near the end of life and should been replaced whenever it next totally fails.
  • Replaced Mt Benson link feeder with known, good LDF4-50 heliax and routed onto cable clips and cable trays to hut. This work was requested by GE to tidy up coax cables on the tower. VSWR 1:1.03
  • Tom VK5EE alerted up the reptile hazards on site at this time of year.
  • Signal tests/S meter readings at VK5MQ QTH shows that there is more signal radiated than before these changes.

Huge thanks to Tom 5EE and Dylan from GE for massive effort today.

Volunteer needed to fix the hole in the corner of the shack at The Bluff. Will be an entry point for nasties. Minor wood working skills required. Have we got a volunteer?

The antenna – two dipole array
The tree towers. ‘Our’ tower closest.
Our antenna just visible facing towards viewer, just below the dish and next to 70MHz array
One of our dipoles visible bottom left corner showing black insulation
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