|During the decades that Roleystone has been
the home of amateur repeaters, a number of interesting experiments have
been conducted from the site.
The 10GHz Beacon
For several years Roleystone had a 10 GHz beacon located at the 200' level and using a horn antenna, radiated a signal pointed West. The power level was 20mW. The beacon was FM modulated with the callsign VK6RGH.
Roleystone 10GHz Beacon
12 volt power was fed up RG58 coax which can be seen in the photograph above. The beacon was all amateur built but the amateur who built it escapes me. The beacon service was discontinued after several years for reasons lost in time..
Roleystone has a 10 element Yagi pointed South for linking the VK6 WIA news to Mt.William and Busselton. This provides a good 2 metre signal to Mt.William some 100 kilometres South and an acceptable signal to Busselton 200 kilometres South.
Chris VK6KCH came up with the idea to use the beam, when not in use by the VK6WIA news, to be connected to VK6RAP 2 metres. This provided a stronger signal to be sent and received by VK6RAP 2 metres.
The beam switching was via DTMF control and a coax relay switched between the normal antenna and the 10 element Yagi.
Signal strengths to the South were considerably stronger and provided increased coverage by VK6RAP 2 metres. The system was disconnected after a trial period.
Mast head Pre-amp
The coax run at Roleystone, due to the height of the tower is considerable, some 280' (85M) from the top to the bottom. Using the best coax we could find, at a price WARG could afford, the loss was 4dB or more. The Pye F60 had a sensitive receiver (Nuvistor front end) but it could be improved by the addition of a grounded gate pre-amp, using the ARRL repeater Handbook design, specifically designed for repeater use. This pre-amp did improve the Pye F60's sensitivity by 6dB and had been used in a double screened box at the original VK6RAP site.
2 metre pre amp from the ARRL FM & Repeaters Hand book
The pre-amp was a two stage grounded gate FET design with low gain of about 15dB. Pre-amps have to be used carefully on repeaters as they can cause many problems to the repeaters receiver, due to the strong repeater's transmitter signal.
The FETs used 2N5484 (MPF106) or MPF102. The FET I used was the TIS88. There would be many UHF FETs that could be used today.
The pre-amp was installed at the very top of the Roleystone tower. Power was feed, either up the coax, or via a separate cable (can't remember) and the repeater's receive performance was increased by 10 dB, yes 10 dB, a combination of the coax loss being eliminated and the improvement to the F60's receiver.
To this day Roleystone has not had a more sensitive repeater.
Antennas used at Roleystone
There have been many antennas tried at Roleystone on the 2 metre repeater VK6RAP. The very first antenna used with the Pye F60 repeater was a commercial folded dipole. The repeater used split antennas one for receive and one for transmit. It was not until a duplexer was constructed that thoughts turned to trying to improve the antenna.
Way back then there were very few options when it came to antennas. There were few amateur commercial antennas and the Ringo Ranger made by Cush Craft was one of them.
Ringo Ranger Antenna by Cush Craft for 2 metres.
These antennas are two five eights in phase with a phasing section (delay) in the middle and end fed by a tuned single loop and parallel capacitor made up by the bottom section. Being end fed meaning high impedance, ground radials are not needed, at least that is the theory. This proved perhaps to be wrong, as several years later Cush Craft released a new Ringo Ranger that had ground radials...!
They are quoted as having 6 dB gain but this must be in relation to a quarter wave antenna, so as compared to a dipole the gain, if all is working correctly, should be about 4 dBD. Worth having so WARG purchased one and it was installed on VK6RAP.
The difficulty in deciding if any given antenna is better than the previous one is, unless accurate tests are done, reports from amateurs can be very unreliable. Just the thought of a new antenna can convince some amateurs that signals are better. Signals from a repeater can vary due to changes in local noise or even weather conditions that bend VHF radio signals up or down even in the main service area. The changes are not great but these changes can be noticed by amateurs and reported as changes in a repeaters performance.
Two Ringo Rangers in phase
Two Ringo rangers connected in phase were made up and installed at Roleystone as shown below.
Two Ringo Rangers in phase at Roleystone.
As the antennas are up side down to each other, the two antennas are 180 degrees out of phase with one another, so the matching harness had to have an extra half wave added to one of the antenna feeds.
The gain should have been about 6 dBD, but as the two Ringo Rangers in phase were replacing a single Ringo Ranger the increased signal strength would have only been 2 to 3 dB. This is not a big increase. Results were difficult to decide upon. Reports from amateurs were mixed and few if any amateurs, who were far enough away from Roleystone, took signal strength measurements before and after.
This further highlighted the difficulty of deciding if antenna changes made a difference and the considerable work to make up and install new antennas was worth the effort.
The two phased Ringo Rangers deteriated over time and were replaced with two phased dipoles which I constructed using the double bazooka design. These dipoles are easy to make and present a low SWR. Constructed from coax and placed inside a plastic pipe they are a great 2 metre antenna.
Double Bazooka Antenna