|WARG is in
the fortunate position of having a relatively large membership and more
money than they ever had in the past. Added to this, there is a wide
equipment that was not available in the past. WARG can now improve and
expand our network like never before.
Cataby 1980s This repeater was once linked to Perth, Mt.Saddleback & Katanning.
This page is to look at the pros and cons of what equipment WARG could use to update and expand our repeater network.
Heath VK6TWO has provided a comparison of the main contenders under consideration for WARG's repeater upgrade and expansion and can be found here
My opinion is, using the Hamtronics option is the best, and hence this information could be biased. However having built at least 12 repeaters, along with duplexers and antennas for WARG's repeater network since 1972, I do have considerable experience and know in detail why WARG is having such difficulty in making a decision, and moving on with implementing their decision....
WARG have been investigating updating our repeater network, primarily looking at our 2 meter systems. The discussion is looking at.....
Along with a new more flexible repeater network, linking our repeater network is also an important part of the updating of our repeater network.
The point of the discussion was to come up with a plan that was the best, not just a little better but the best for many years, even decades to come.
The most important issue is, what ever equipment is used, we need to understand in detail, the complex requirements. A single repeater is by comparison simple. When you decide to link repeaters and / or interconnect repeaters together on the same site, ease and flexibility of doing so is crucial. Added to this is the WIA news, which adds a further level of complexity.
The discussion has now been over several years and 3 possible directions to consider have been floated.
1. Using modified ex commercial equipment
The main issues with using ex commercial equipment is finding enough suitable radios and to look far enough ahead to future availability of ex commercial equipment. There is a real problem with ex commercial equipment not being available in sustainable numbers over many years, most probably decades.
Ex commercial equipment can simply not be suitable because.
However my experience over many decades is not to use ex commercial equipment. It really only has one main advantage and that is cheaper price. But if you examine the total price there could well be little advantage, as an amateur repeater requires many extra considerations, like rack mounting, control board, remote control and link interface. The ex commercial radio may well not save as much money as might be first thought, mainly due to finding work arounds to various limitations.
2. Using new commercial equipment
This option is expensive but the modern commercial rack mounting base station - repeater is of exceptional design and overall performance. As a straight repeater they all would work well as a basic amateur repeater. One limitation is however, some commercial repeaters use phase modulation rather than direct frequency modulation and as such have higher audio distortion levels up to 10% at full deviation. This in a single repeater is not of much concern but linking systems together compounds the distortion from end to end.
However new commercial repeaters are a basic repeater when we look at amateur requirements. A repeater in its simplest form is just a receiver and a transmitter connected together to repeater the incoming signal from receiver to transmitter. In the amateur situation only two licence requirements need to be added and that being time out and callsign identification. Many commercial repeaters meet these two basic requirements.
WARG are looking at all options for an up to date repeater that meets the significantly different amateur needs, when compared to commercial requirements. Linking is high on the list and some commercial repeaters do not have the required in - outs on an accessory socket. Also the built in time out and CW ID have to be disabled, as we would most likely use an external control board for all our control and interface needs, such as linking. Disabling time out and CW ID most likely is as simple as a program change but we have to be sure this can be done.
I have many reasons for not favoring using new commercial equipment, but above all is the complexity of the modern new commercial repeater. These modern radios are packed full of a wide range of fantastic facilities and options. However many of these options we do not need. They complicate the radio unnecessarily, use more power, make it more difficult to interface with if we need to make connections direct to circuits within the radio, and make it difficult to fix.
We have to keep in mind that we are looking at the long term, and future amateurs will be required to fix and maintain the network. Handing on a complicated radio for others to fix and maintain is not the best option. Amateurs more and more are coming into the hobby with less technical skills. The nuts and bolts of how a radio works and how, at component level, to fix and test such radios is being lost overall in amateur ranks.
These new commercial radios are reliable and do come with a warranty. However warranties run out and companies come and go, as does a particular model radio. Just because a particular manufacturer gives us promises, should not lead us to a false sense of all is well in the very long run. We are looking at perhaps decades of use. The FM880 is now 2 decades old...! Will the commercial companies still be there in 20 years time...!
3. Hamtronics Option
This is the option I favor and have long held the position, primarily because it is simpler.
To begin my reasons for this opinion some explanation as to why WARG's repeater network has been in decline.
WARG's repeater networked, both linked and stand alone, has been in decline for at least a decade. So why was the network expanding during the 1980s and 1990s and now in the past decade in decline...?
WARG not only rebuilt and expanded its 2 metre network but also started to link repeaters. At one time many repeaters were linked.
The reason for this decline is mainly equipment. The link equipment used was amateur converted commercial equipment. A decade or two ago there were limited options with equipment and often the choices were poor and they failed. Endless traveling to sites to try and patch up poor quality equipment, and in some cases design, just became too costly and difficult, simple as that.
So not to repeat the earlier failures, equipment is the most important issue. Reliable but simple link radios if we want an expanding linked repeater network.
Back to the Hamtronics option
Hamtronics is an American company that produce high quality stand alone receiver, exciter and PA modules, along with various pieces of repeater control boards, DTMF controllers etc, the list is a long one...And they are designed primarily for the amateur radio repeater builder. And they have low idle current, most important for our solar sites. Also both VHF and UHF units are available which allows for 6 metre, 2 metre and 70 cm repeaters to be constructed that are the same, except for the frequency band they operate on. Plus the UHF units would be our link equipment......
One design for all our needs, including linking....!
Hamtronics Receiver (new version)
To have the best repeater there is a range of requirements. One of the most important is the mute performance of the repeater's receiver. Amateur radio is in part about getting the most from the least. Amateurs will dig a signal out of the noise because that is the nature of Amateur radio.
So is it with the repeater's receiver. To hold onto a weak mobile or hand held signal requires a sensitive receiver, no desensing from the repeater's transmitter and a good receiver mute.
Not all mutes in FM receivers are the same. Some chop up a weak mobile signal while others hang in there and repeater the weak signal at a higher readability. The reasons for this are several, such as mute stability, sensitivity and mute hysteresis. Too detailed to go into here but most important.
The Hamtronics receiver has been designed with this in mind. Not all commercial radios are, because commercial radio sets a higher signal level as the minimum. Noise free is the design intention. Weak signals just annoy the users and they complain.
Hamtronics offer a proportional mute, one that adjusts switch off, depending on receiver signal strength, such as weak mobile signals. The current FM880 repeaters have a simpler version of this proportional mute. I don't know of any commercial radios that do, but some may.
If we go the commercial way we need to test the receivers mute performance before we decide on a given commercial repeater.
Below are a series of videos testing the Hamtronics VHF receiver.
Hamtronics VHF verses FM880 (828)
Hamtronics power supply test
Hamtronics receiver temperature test (-3 to 43 degrees C)
Hamtronics Exciter - 2 watt output
What you see above could be connected up as a basic repeater with 2 watts output......!
The point has been made, why not use high current commercial units at mains powered sites and Hamtronics at solar sites...? Good point but this is less flexible in that we now have two different types of repeaters, rather than concentrate our limited resources on just one design.
Several Australian repeaters have been built using the Hamtronics repeater units, even some in VK6. All units, receiver, exciter etc come ready built, all that is required is to place them in a suitable rack mounting box and connect them up.
Voice repeaters, in their basic form, receiver, transmitter and control board are not that complicated. Most if not all amateurs could, given the right direction, put together a voice repeater using the Hamtronics units. Later additions, like linking, can easily be added as this interface is built into most repeater controllers.
The Important point is the simplicity of easy to see and access printed circuit board units. Commercial alternatives have a lot going on, often on one complicated circuit board. If connections are needed to these circuit boards, due to the lack of in out rear panel connections, it can be difficult to find the right points and difficult to make the connections to surface mount boards. You run a high risk of circuit board damage.
I can not emphasis this point enough. Remember we are not designing a new repeater network with linking just for amateur's who are available now, but well into the future. Amateurs come and go for a variety of reasons and we could well have the capability to put together a new commercial repeater network, along with the computer program interface, but we may not years down the track be able to keep it going.
And the very thought of having to rely on commercial sources to fix or modify even a small part of our repeaters or network horrifies me. May never happen but if we use complicated commercial radios it could.
The Hamtronics Project
If we decided to use the basic building units, which are....
With less amateurs being able to take on such a large project, for a variety of reasons, it is an important question to be asked. No point in buying all the equipment and then letting it gather dust year after year, while we wait for "them" to get on with it.
The way to approach, what is a big undertaking, is good management. Before any building takes place, a step by step plan, with information and diagrams needs to be done. I have already made a start on this and would offer to progress this with a more detailed plan of construction.
It is so easy today to circulate information...Even a step by step video could be made to show the construction...I have the HD camera and with Youtube, easy to make available.
This is my idea on how such a large project could be broken down into easy stages....
Firstly we don't have to make many repeaters or links at the beginning. Perhaps 2 repeaters (2 metres) and 4 UHF links. We need links more than we need repeaters at this point.
Decide on a rack mounting container. I would use the di-cast box option shown below.
Do the drawings that show the rack mounting box and the layout and positions of the various component items as already done below.
Rack mountable di-cast boxes used to house repeater...Larger view
Rear repeater in - out link and WIA news interface not shown yet.
Di-cast is an easy to drill and work material. In the picture above, as luck would have it, 3 di-cast boxes can be bolted side by side, and along with a front panel make up a rack width, easy to access RF tight container.
Fit control board to center box
All wiring would be colour coded...For example all 12 volt is in red and earth in black. Audio out green, audio in orange etc...
Stage 4...The PA
The design presented so far is for a 2 watt repeater or link transceiver, as the Hamtronics exciter has a 2 watt output. Interesting point about the 2 watts is flexibility.
We may find a use for a 2 watt repeater as is....For example to provide limited coverage in a particular city or country area to fill in a poor coverage area from existing repeaters, and this local area repeater is then linked to a wide area repeater.
And the 2 watt UHF version makes a useful link where higher power is not needed.
To finish the repeater for normal use a PA (RF power amplifier) would be added. The design layout has room for a PA as is. Extra heat sinking would be added as required to the underside of the transmitter box. The nominal 25 watt PA would work well with this design. Higher power PA's could be housed in a separate rack mounting box with the extra heat sinking they would require.
Hamtronics sell a single stage transistor PA designed specifically to raise the 2 watts to 25 watts. The price at $250 is high for what you get and this could be manufactured for about half this price.
Along with the Hamtronics PA there are other options....
VHF and UHF power modules could be used. Most (if not all) require only milliwatts input (20 to 50mW) to produce various power outputs. This would require an RF attenuator to be added between the Hamtronics 2 watt exciter and the PA module. This is just a resistive attenuator. A bit wasteful power wise but an option.
The old FM828-880 PA
The FM828 - 880 uses a 4 stage PA that takes about 50mW and produces an output of 25 watts. The output transistor is a BLY89a and is run way below its maximum output of 50 watts. As such the PA does not require any SRW protection. These PAs are very reliable.
WARG have a lot of these 2 metre PAs and they are a stand alone unit that is easily separated from the 828 or 880.
They could be used with the Hamtronics 2 watt exciter to provide 25 watts output. As the exciter puts out 2 watts, two options could be used to match the exciter to the 828-880 PA.
Resistive attenuator between the exciter and PA, or tap into the PA, at the driver transistor, between the 2nd and 3rd transistors.
This would be a no cost alternative to the Hamtronics single transistor PA or one we make ourselves.
Watch the video of the Hamtronics units mounted inside a rack mounting box
As I have said my bias is towards the Hamtronics option...Reasons..
Having taken the time to write up this proposal, perhaps anyone with a different opinion could do a similar argument for either of the commercial options.
The author, Will VK6UU Setting up microwave links for TV OB