VK6RTH Tic Hill Circuits

There are 2 voice repeaters at Tic Hill and one digipeater

VK6RTH 2 metres 146.200 receive 146.800 transmit
VK6RTH 70 centimetres 433.225 receive 438.225 transmit
DTMF equipment power on/off control

Circuits are available for the 2 metre repeater only at this time.

VK6RTH front panel

Front panel of VK6RTH....Tony VK6YAG did the front panel improvements

VK6RTH 2m inside

VK6RTH 2 metres inside view

VK6RTH underside

Underside of VK6RTH showing RX & TX boxes plus the audio message logic board that is not used.
This board was used way back when VK6RTH required a CTCSS tone to access the repeater due to interference problems.
Any signal with out a CTCSS tone received the voice message that the repeater required the 123HZ tone for access.

VK6RTH block diagram

The block diagram above is of the original VK6RTH 2 metres but there have been considerable modifications to VK6RTH and they are below.

VK6RTH issues & modifications....2003 by Tony VK6YAG

During 2003, VK6RTH 2 metres, had a number of issues, which were in simple terms, a dead receiver along with a previous history of the repeater's mute remaining open for periods of time. Tony, VK6YAG, took on the task of sorting out the problems with VK6RTH 2 metres.

The receiver was dead and had to be replaced. This was easier than trying to sort out what was wrong with the receiver board. Lightning damage was suspected and this could have resulted in several faults with the receiver board hence the easy option of replacing the receiver board.

The next "fault" condition was the mute remaining open with a noisy signal for periods of time. Tony tracked this down to the URC101 control board, which it was discovered, radiated a low level carrier on 146.200 MHz (and some other frequencies). The signal did wander a bit in frequency, but when it was on 146.200 MHz, the mute would open on VK6RTH.

URC101 copper screen

URC101 control board shield...VK6RCT shown

Tony has since fitted the copper screen box to VK6RCT & VK6RAV


VK6RTH URC101 control board with top screen cover removed.

Also there were some issues with low battery voltage at Tic Hill. Changes to equipment at the site had seen the power budget rise considerably and the solar system did not last well enough through the winter.

A 9 volt regulator was added to supply power to several of the circuit boards. There is a good low volt drop out 10 regulator in the FM880, but the 9 volt low drop out regulator gave some extra head room, while the battery supply problems persisted during winter.

Also the speaker amplifier and weak mute board had failed as well, so Tony installed a speaker amp in place of this board and a separate weak mute board which is now located in the receiver compartment. Also installed was a audio mute switch for the speaker audio and the transmitter audio.

VK6RTH extra boards

Extra boards inside VK6RTH....Audio muting & weak signal mute

VK6RTH new speaker amp

New speaker amp...Was speaker amp & weak signal mute

Transmitter frequency drift

VK6RTH had also been showing transmitter frequency drift of as much as 5 KHz. The drift was tracked down to the transmitter crystal and it was found to be temperature sensitive.

Tony fitted a small temperature controlled oven that raises and maintains the crystal at a constant temperature, about 40 degrees C.


VK6RTH temperature controlled TX oscillator surrounded by styrofoam.

VK6RTH mods-1

A 9V low voltage drop out regulator was fitted to feed the various circuit boards and new speaker amplifier.

VK6RTH FM modulator mod

Modifications to transmitter FM modulator.

VK6RTH modifications block doagram

Block diagram of modifications to VK6RTH...Note also done to VK6RAV

VK6RTH 2 metres is of the FM880 design. For a detailed description of the FM880 design go to FM880

There are some unique differences with the VK6RTH FM880. This is as a result of the repeater operating for a long time at Tic Hill and having a range of situations that required circuit additions.

For a period of time VK6RTH 2 metres had to be changed to CTCSS input due to interference to the repeater. A 123 Hz CTCSS tone was required to activate the repeater for normal voice operation. To inform users of the change a voice message was added. If the repeater was triggered without the required CTCSS tone a voice message was transmitted to let users know of the CTCSS requirement You could not talk through the repeater just trigger the message.

Also added to VK6RTH 2 metres is DTMF control of other equipment. The 12V power can be switch on and off to all equipment (except VK6RTH 2 metres) at Tic Hill.

VK6RTH 12V power control

VK6RTH voice logic control

The circuit above is of the logic interface for the voice message that was on VK6RTH many years ago due to a CTCSS requirement. The actual digital voice unit's physical location is unknown. The circuit is included as the interface circuit above is still in VK6RTH 2 metres.