Reader's Comments, on the Discone Antenna

HF discone question / comment....

Greetings GVARC

After viewing your web page, I could not help but want to contact you and make a comment about the HF discone antenna you have displayed and use in your club activities. Please bear with me as I jog my memory a bit, going back about thirty years. My name is Rodger McIntyre and I was stationed at Davis-Monthan AFB from November 1975 to December 1978 in what was first, the 803rd Communications Squadron, later redesignated as the 390th Communications Squadron. I was assigned to the HF-SSB/UHF maintenance unit. I was enlisted in AFSC 30454-1 or, GROUND RADIO EQUIPMENT REPAIRMAN, having trained at Keesler Technical Training Center, Keesler AFB, MS from January to October 1975. The "-1" suffix was designation for the Titan II Ground Radio specialty. The 30454-5 designated group were trained for and bound to Minuteman sites.

Anyway... our HF group maintained a rack of gear which resided one floor below the complexes command center. The HF "rig" was a Collins 9000 series exciter, 2 to 30 mHz AM, USB and LSB capable along with a 250W RF amp, capable of 1000W peak in the sideband mode of operation. The equipment had several auxiliary pieces, of course a very hefty power supply for the RF amp, and at the output, a coax switch operable from the remote HF control panel on the launch control level at the DMCCC's duty station.

The RF output was normally fed to the "soft" or surface (discone) HF antenna. During PM maintenance, the RF output would be switched to the stowed or "hardened" HF antenna for a radio check as well as a check of the soft antenna. The hardened antenna was designed for use once or perhaps twice following, and in the event of a "hit" as a hit would cripple or destroy the soft antenna.

The hardened antenna was controlled by and had to be extended to tune it to the selected frequency. Once the operating frequency was selected, the hardened antenna would essentially "auto tune" via a syncro controller module, mounted within the HF control panel. It's vertical up-down behavior could be loosely compared to "up-periscope" and "down-periscope" on a submarine. The hard antenna's mechanical drive was a series of guide rollers driven by automobile-size tires surrounding the telescoping mast, which were coupled to a drive train, subsequently driven by two 440VAC three phase industrial size motors, about two-hp. Myself and other ground radio repair techs maintained all of this equipment, performing periodic PMs on the transmitter and on both the hardened and soft antennas.

The rack was inspected on a 28 day PM cycle and I believe the antennas were maintained on a 60 day or similar PM interval. Any rack equipment that failed to meet minimum specs was pulled or R&R'ed and went back to the shop where we performed bench electronic troubleshoot and repair to the component level, along with RF re-alignments and certifications to return the defective unit to serviceable condition.

The hardened, stowed antenna required fairy involved maintenance with it's launch and stow drive apparatus, but the soft antenna maintenance was mostly coax cable and RF connector inspection, cleaning and replacement of RTV as needed. The transmitter's VSWR check was the main indicator of the antenna's ongoing RF cable integrity along with a thorough visual inspection of the assembly, especially the non-metallic stand-offs supporting and spacing the radiating elements from the frame.

Best Regards,
Rodger McIntyre
Tucson, AZ

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