VK5RMG Mt Gambier

Left cabinet: VK5RMG 2M with new touch graphic display in lower Tait chassis enables touch control on site. Right cabinet: DC switching for 2M and UHF, 2 power supplies and the black Yaesu Fusion digital repeater. Backup batteries bottom.
An early working bee at The Bluff to install antenna

VK5RMG, located between Millicent and Mount Gambier is our main hub two metre repeater. It is located on The Bluff, approx. 200m ASL. We recognise the support of Gambier Electronics for the use of the hut and tower. Their help is much appreciated.
Lat.  37deg 43min 52secS     Long.  140deg  34min  12secE

The input is on 146.300MHz and the output is on 146.900MHz at 25 watts.

Currently, the 91.5 Hz CTCSS tone is required to access this repeater. A transmission on VK5RMG is relayed to VK5RNC, VK5RKN, and VK5RBT through UHF links.

UHF Link to Naracoorte on 442.375 MHz
UHF Link to Mt Benson (between Robe and Kingston) on 430.475 MHz
UHF link to Mt Eckersley (near Heywood) on 449.875 MHz
An additional controller has been manufactured to enable a third link to Western Victoria.

The latest four channel system has enabled us to go without the old audio bridge that served us for many years but proved difficult to set consistent audio levels across repeater and links.
Below the link transmitters are the cavities – six of them, three for the receiver with a notch at 146.900MHz to remove the transmitter signal, and three for the transmitter with notches on 146.300MHz to reduce noise from the transmitter entering the receiver.

The repeater has good coverage of the Lower South East of SA and some distance across the border into Victoria.

The 2M transmitter runs 25 watts while the link TAIT transmitters run 4W/10W respectively into 10 element yagis pointing at Naracoorte, Mt Benson and Mt Eckersley.

The main repeater antenna consists of two commercially made vertically stacked folded dipoles.

The new controller (designed and built by VK5DJ, VK5BW, VK5VI) allows remote functions that include the transmission of a tune up tone of 1kHz tone at 3kHz deviation. This is invaluable for adjusting remote receivers for consistent levels across the network. In addition the new controller also has a better CTCSS decoder that may be activated or even changed in frequency if necessary.

CTCSS will not be in use unless necessary, but when there is persistent interference (usually from unstable TV preamplifiers in Mount Gambier) or co-interference from other on site transmitters, we will be able to lock the interference out and yet facilitate communication in the normal way.

Currently the CTCSS frequency is set for 91.5 Hz. It is good practice if users have 91.5 Hz tone activated on their transmitters at all times so they won’t be caught out when CTCSS is activated.

Col VK5DK, Charles VK5HD and Andrew VK5KET at The Bluff
The Mk2 VK5DJ controller and audio recorder.

At top the main interface contains a PIC18F2480 providing a display driver and audio and voltage levels for display – previously on LEDs and now on a small OLED display.

Centre the voice recorder (ISD1760 chip) driven by the interface board.

Bottom is the controller itself providing all control functions, audio amplifiers, DTMF and CTCSS.

All connections via I2C to front panel devices.

Three DB15 plugs on rear of chassis feed the main repeater, the link to Naracoorte and interface to the link expansion controller in a separate sub chassis.

A Brief History

  • The first VK5RMG 2m repeater was built by David VK5ZOO in the late 70s. It was installed first on a local tower and then at the SES8 TV studios. It suffered desense and was not successful. It ended its life at David’s workshop on a shelf. No repeater was on air until 1982.
  • The Bluff repeater was installed on 7 August 1982 in Hutchesson’s Hut courtesy of Trevor (VK5TH) of Hutchesson’s Electronics. It ran from batteries charged by Trevor’s wind generator. Repeater designed and built by John VK5DJ with metal work by Trevor VK5NC. Mostly Phillips 1680 parts with logic etc with individual chips. Had simple DTMF remote controls e.g. low/high power (2.5-17.5W), timeout control, shutdown etc. The following are extracts from the log book.
  • Various adjustments and one failure in a 4017 chip later 1982. Interfering carriers, re-adjustment of cavities.
  • 9 February 1983 fault in no 3 TX cavity loop, resoldered and fixed the occasional desense.
  • 19 May 1983 dismantled and reboxed University of Adelaide’s seismograph TX in lookout tower on 450.325MHz and retuned to overcome birdies and increased TX power as a result. Revisit on 4 June to bypass the power supply of the seismograph TX – all now happy.
  • 24 February 1985 replaced Scalar Antenna (fibreglass collinear type) with Ringo temporarily for factory rebuild of Scalar. Repaired heliax connector.
  • 5 May 1985 returned Scalar to old spot, insulated base (noise from movement was a problem with the Scalar). Mute opens 0.14uV and closes on 0.08uV.
  • 12 October 1986 new antenna by RFI, also water in coax. Much corrosion in base of old antenna.
  • 30 May 1987 more antenna noise problems. RFI antenna pulled down and original repaired Scalar returned. These radome collinear antennas can’t stand the wind turbulence.
  • 13 December 1987 RFI antenna back again. Supports cleaned and painted.
  • 13 January 1988 AC available and power supply installed with AC fail in controller.
  • 11 February 1990 RFI antenna and bracket removed from tower and cleaned. Problems with antennas continued. Another replacement on 14 November 1990.
  • During 1991 various power supply issues. One fault was caused by the meter switch when moving from volts to amps causing a short.
  • 15 February 1992 put a temporary 160MHz groundplane and retrieved collinear antenna for repair. Antenna re-installed 30 May.
  • 17 April 1995 replaced antenna with new RFI collinear
  • 16 December 1997 re-silvered the cavities.
  • 30 January 2000 installed two phased dipoles.
  • 7 October 2000 new repeater installed using PRF1520, new controller NHR2.
  • 9 October 2000 failed audio on TX – fixed, then later a faulty N-type connector replaced.
  • 29 October 2000 installed UHF antenna to Naracoorte and link on 442.375 ready.
  • 2 December 2000 link to Naracoorte operational.
  • 26 January 2001 repairs to 2M preamp to reduce instability
  • 12 February 2001 replace tails to heliax with RG214 and to RX and TX from cavities with RG224. Easier to manage and double shielded.
  • 29 March 2002 birdy into 2M. Traced to internal switch mode power supply in PRF1520. Made it crystal controlled and fixed problem. Backup battery installed.
  • 24 March 2003 main antenna moved to taller tower.
  • A gap in the records until 1 February 2012. Interference from Aussie Broadband – broad noise across 2M. Company fixed faulty unit.
  • No record of when link to Kingston and then Mt Benson was instigated. Links changed to Tait units 4 October 2014, as there had been problems with PRM8030 units overheating. 8W to Mt Benson and 4W to Naracoorte. Controller upgraded to VK5DJ Mk1.
  • Volunteers attending working bees at the site over the years up to 2012 include VK5NC, VK5DK, VK5MQ, VK5ZX, VK5HD, VK5HDW, VK5OA, VK5TH, VK5KBF (now VK5BE), VK5AKJ, VK5ZCP, VK5HBA, VK5ZCH,VK5FF, VK5PXK, VK5KAF, VK3YYV, VK5BVN, VK5EE, VK5DG, VK5KMP, VK5HOS, VK5KET, VK5NSE, VK5WCC, VK5GL, VK5AV, VK5HCF, VK5ZWC, VK5NDD, VK5ZOO, VK5MOO, VK5LAC, VK5ANC, VK5BCB and dad Nick,VK5NJ, VK5MAS, VK5KJ, VK5FNBL, VK5MQ, VK5KGB, VK5HAY, VK5ZGY, VK5FORS, VK5TN, VK5MC, VK5VKC, VK5FLAR, VK5ZAI, VK5VI, VK5NFT, VK5DJ as per the memo book used for this report. There will be missing entries so apologies if anyone has been left off the list. Let me know and I’ll add.

    John VK5DJ
    Repeater coordinator
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