|This proposal is to detail how several
country repeaters, within UHF range of Roleystone, could be linked with
a minimum of equipment. The idea is based on the previous linking that
was done from Roleystone to Cataby and Mt.Saddlebck, but is expanded to
include other country repeaters.
See block diagram below......
The concept is not new and is, at least in part, what WARG intend doing, particularly as the Mt.Saddleback linking equipment is already built and awaiting installation. What I have added is an expansion of the network to include Hoddywell and Mt.William.
A similar linking hub is operational at Mt.Barker in the South linking several VHF repeaters.
The most important aspect of this network is for it to work well. When you link a large number of repeaters, what ever happens on one repeater is reflected right through the network. Particularly if the concept is for all the repeaters to be linked at all times.
The most important part of the network is the central linking hub at Roleystone. This is a normal repeater and is working now on 434.8 receive and 439.8 transmit.
This repeater requires the following......
Past experience with the most difficult part of the link was with Cataby. The distance is 155 kilometres and the path is marginal. However the previous link did work and only requires about a 6dB improvement for reliable noise free linking.
Where this can best be achieved is at Roleystone. LDF550 coax is already run and this would result in a 2dB improvement. The previous coax was part LDF550 and part LDF450.
The antenna is where the greatest improvement may be made. I have always been skeptical of amateur commercial antennas, particularly the multi band VHF - UHF ones. They offer several bands on one coax, but do they work as well as the manufacturer would like us to believe...? For starters they often quote dB gain figures with reference to an isotropic radiator, which adds 2 dB of gain to the antenna as compared to a dipole. This is deceptive as we use a dipole as the standard antenna and no one makes and uses an isotropic antenna, even if you can.
Asking around on various email reflectors, about how well these multi band antennas work, results in little feedback. What I have had supports the dipole antenna as being better than the multi-band antenna.
Even if you do some research on the net, as to which multiband is better than another multiband, you get a wide range of results. Some are better than others, even though they are the same size and quoted gain figures. All in all very unreliable to base an important aspect of a linked repeater network on antennas that may not work as stated. And in particular the central linking hub at Roleystone.
UHF antenna at Roleystone
Tests need to be done to find out just how well the Roleystone UHF repeater on 434.8 - 439.8 is radiating. I know at my QTH the UHF repeater is way down on VK6RAP 2 metres, but this may be an issue at my end. Testing I have done show VK6RAP UHF is 22dB down on VK6RAP VHF.
If required I would change the UHF antenna at Roleystone being used by 434.8 - 439.8 to at least a two dipole array. Four dipole array would be better but may not be needed. Quarter wave mounted out from the tower the gain is 6dB, genuine. The antenna pattern is cardioid so you don't get the 6dB in all directions, but with the correct placement those distant repeaters requiring the most signal strength could be optimised.
With so many repeaters being linked, there are some amateurs in the country areas who may not want their local repeater connected to the linked network. This is difficult to understand, as many of these country repeaters lie idle for 99% of the time. And the linked traffic is other amateurs.
However to respect this opinion, ways can be found to overcome this problem.
This is how it could work, so local traffic when required, is local traffic only.
The local country repeaters are equipped with "reverse CTCSS" for want of a better word. Rather than turn on the CTCSS to link, you turn on the CTCSS to not link. Any amateur who wants only to contact local amateurs on the local repeater encodes there transmission with a given CTCSS tone. When the repeater receives this tone, the linking from this repeater is inhibited. The repeater is a stand alone repeater when ever the user has the required CTCSS tone on their transmission. Any amateur in the local service area who wants to reply to the call also enables the required CTCSS tone and a normal local only QSO takes place.
This CTCSS tone could also disable incoming linked traffic along with a time delay before the repeater reverts back to normal linked operation, say 15 seconds. This prevents any linked traffic from interrupting local QSOs between overs.
Also CTCSS encoded on the repeater could be used so local users don't hear linked traffic if they so desire.
To give an example...
Two amateurs who only want to hear local traffic and communicate with local amateurs, encode their radios with the same CTCSS encode decode frequency. The encode turns off the linking.
The CTCSS encode on the user radio also places a CTCSS tone on the repeater's transmitter which will only open the mute on the other amateur's CTCSS decoded radio. Hence the two amateurs only hear each other.
What happens if the link is operational......?
The two amateurs would not know this and simply transmit. Unless another amateur in the service area was in a linked QSO or was listening to a QSO this would not be an issue as the linking is simply turned off.
One would say that the two modes of operation are incompatible, and this is true up to a point, but with the low usage of many country repeaters I don't see this as much of a disadvantage compared to the dual function use of a repeater that can be linked or not linked and yet be user friendly.
You might ask why not do the reverse and require a CTCSS tone to turn on the link..?
The advantage of the link always on and not requiring a CTCSS tone is, any amateur traveling through the area, unfamiliar with the repeater situation, only needs to be on the repeater frequency to make contact with amateurs far and wide. End result a greater chance of a QSO and greater use of idle country repeaters.
However......Reversing the "Reverse CTCSS"
If the reverse CTCSS idea is not what is wanted, then the more conventional normal CTCSS to turn on the link could be used. Local users then don't need a CTCSS tone to operate the repeater for local contacts and don't key up the link.
There are many options with CTCSS and it could offer the ideal usage and an amateur could choose their operating preference....To be linked or not to be linked....Even as discussed above, not to hear linked traffic and not even know there is a link.