146.1 - 146.7
Chapter 2
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The chip board cabinet had a Sun roof fitted at some stage to keep as much water off as possible. After a couple of years a 5'x5' garden shed was placed over the top of the cabinet to improve the life of the cabinet. Some water had effected the chip board but over all it had done a good job. Eventually the chip board cabinet was removed and unceremoniously dumped a short distance from where it had given shelter to Perth's first repeater for a number of years. |
The remains of the chip board cabinet
The garden shed.
| This garden shed remained for
about 15 years before it was
replaced
with the existing much larger enclosure. The inside of
the garden
shed
was insulated and at a later date had an air conditioner fitted.
|
VK6RAP Mark 2
1970's
|
The Pye F60 had done a great job and had accelerated VK6's first repeater getting on air.
Shown above is a poor photograph of inside the shed at Roleystone, showing the two IC22a repeaters in the bench top rack with duplexers below. Bottom right is the only photograph found so far of Perth's first voice repeater, the Pye F60. A person is kneeling down and is blocking most of the view. All along the intention had been to replace the Pye F60 with a solid state version. The VHF group had designed and provided kits for building a 25 Watt FM mobile. This design was chosen to build up a solid state 2m repeater. Such a repeater was built and proved to be limited in its performance. The new solid state repeater worked but receiver performance was not as good as was required. Also the transmitter had a noise output that could be better. However this design did provide service for a number of years and was WARG's first development of a solid state 2M repeater. The exciter design is still used as the VK6 WIA news link transmitter from Roleystone to VK6RMW Mt.William |
The Duplexer
| Repeaters in VK6 on 2M all began with split
antennas, one for receive and one for transmit, spaced vertically at
least 50' (15M). This worked well but required two coax feeds and two
antennas. It was inevitable that thoughts turned to building a
Duplexer, a device that allows the repeater's receiver and transmitter
to share the same coax and antenna. Duplexers are very sharp notch filters, one section has a notch on the transmitter's frequency and is placed in the receiver's input and the other section a notch in the receiver's frequency and is placed in the transmitter's output. Duplexer's are such an important and difficult part of maintaining a good repeater that a section on WARG's 2M duplexer is to found here. Not a lot was known about duplexers, but what was known is that a lot of dB separation was needed between a repeater's receiver and transmitter, some 80 to 100dB....! a lot. That is to say the transmitter's 20 watts, for example, has to be reduced to about 0.001uW (microWatts) going into the repeater's transmitter...! The numbers in terms of dB isolation are huge. The original VK6RAP, the Pye F60 had a nuvistor (mini valve) front end and a very low noise valve transmitter that only required about 50dB of isolation. However transistors are less tolerant to strong signals and noisier when used in transmitters. |
