|The Cataby repeater site has undergone a
major upgrade. The following components were replaced....
The concept of the upgrade is to produce a high power repeater. With all the various components working an ERP (effective radiated power) of 1000 watts is possible. The repeater that has been in operation since 1984 has a ERP of less than 60 watts....
For the moment the repeater has been reduced in power to produce 50 watts out of the duplexer, the PA running at 70 watts.
The past repeater has a transmitter power of 23 watts. With the repeater running at 70 watts this produced an increase of 4.5 dB.
The new antenna is a complete change in design, from the existing co-linear to a 4 dipole array. The co-linear has 6 dB omni directional. The 4 dipole array is not omni directional but a figure 8 pattern with the major gain North and South. The reduction in gain to the West and East should have little effect, as there is little or no operation from the East and the Western coverage is limited by the Indian ocean. It could be with the extra power no difference will be noticed.
However what we gain from the 4 dipole array is an increase from 6dB North South to 10dB (perhaps more) North South.
So with the increased power producing 4.5 dB and the antenna change producing 4.5dB equates to a 9dB increase. However this figure may be on the optimistic side. An overall increase would be at least 6dB.
Half wave spacing of a dipole produces the figure 8 pattern. 4 dipoles with 1/4 wave spacing have a gain of 9dB. The half wave spacing produces more gain in the North South direction. The 10dB as mentioned above could be more, perhaps as high as 12dB.
A most interesting experiment
VK6 has not had a "high" power repeater. Powers of 20 to 25 watts are the norm. Just how much further the service area will be is yet to be seen. Of course to gain the most from a system like this requires amateurs to run powers as close to 50 watts as possible. 50 watt equipment is common and should gain the best advantage of this interesting experiment.
Equipment rack inside Cataby shed
The new receiver is a Simoco SRM 9000.
The transmitter is a Motorola MaraTrac
The all important repeater controller is the NHRC-4. This controller gives a lot of remote control capability, most important for a remote site. All the repeater's functions such as call sign, time out, shut down etc can be controlled remotely.
All the various components in a repeater are equally important. If any one is not performing then the repeater does not perform. The duplexer is crucial in so many ways in a repeater. It has to isolate the receiver from the transmitter, and even more so as the power is increased to 100 watts.
The new Cataby duplexer is using 6" (15 cm) which have a higher Q than the 4" (10 cm) ones that it is replacing. The overall pass attenuation is better than 2dB and the notch attenuation better than 100dB.
Replacement duplexer for Cataby
It was originally intended for the 4 dipole array to be mounted half below the top of the mast as shown below. The height of the Cataby mast is 60' (18m). However consideration about the strength of the mast has change this to mounting the antenna lower down as shown in the photographs.
Original mounting consideration
New CoaxThe replacement coax will be LDF-450 terminated to multiples of the TX wavelength. The connectors are Andrews compression terminations. Building entry via a gas discharge surge protection, then a wavelength terminated patch cable to the duplexer.
External coax entry point into building
Internal coax entry point showing gas discharge surge protectors
Solar Power Supply
Cataby is a solar site. If the power system does not work then the site is off air. The equipment used is listed below.
New DC power system consists of,
6 Sungel 2SG650
batteries. 2v cells……650 a/h
Plasmatronics PL20 Solar Regulator.
30 Day History, High volts, low volts, A/H in , A/H out.
User defined equalization, float, boost and low volts cut out parameters.
Fully Programmable to site requirements.
1 200w Solar Panel.
14 amps available in full sun.
Battery supply at Cataby
Battery supply at Cataby