This document is intended to give you a basic understanding of our repeater systems. My goal is to make this easy to understand for any licensed amateur radio operator (you did study for your exam, right?). The system contains much more than is shown here and there is a whole lot more functionality. But, for now, let's start simple and build your knowledge from a good foundation of the basics. When we're done you'll have all the knowledge necessary to effectively use our systems to the fullest. Notice that I've included plenty of links that should help explain any terms you might be rusty with. For a refresher on repeater basics please take a look at what I've written on the subject.
Before we talk about the radio portion of the repeaters, let's briefly talk about transceivers. Chances are that most any radio you have for amateur radio use, be it on HF, VHF, UHF or above, is what is known as a transceiver. They call it this because the circuitry inside works as either a transmitter or a receiver. If you like to build your own QRP gear or you are a fan of the older radios from before the 1980's you might use separate transmitters and receivers, but these days that is the exception and not the rule. Most amateur radio operators either transmit or receive at any given time, not both at the same time. So your average mobile or portable radio is constructed in such a way that it is either a receiver or, when you key down, a transmitter. This allows the radio to reuse components, does not require expensive and bulky filtering and is the best bang you get for your buck. Therefore the radio you operate is much smaller and much less expensive than it would be otherwise.
The basic concept of a repeater is that it receives a signal on one frequency and, at the very same time, transmits what it hears on another frequency. Since a transceiver can only transmit or receive at any given time, it would not work by itself as a repeater. Sure, you could use a transceiver as the receiver and another as the transmitter...and some folks do. But this is wasteful when you consider that one used as a receiver would never make use of the transmitting components, and vice versa. There are a host of other reasons that it is not a good idea to use transceivers as part of a repeater, but that gets technical and is better discussed elsewhere. For now let's just stick to the fact that our receiver needs to be independent because it needs to be receiving all the time, even when the transmitter is transmitting.
Please take a look at the following diagram:
At the top, in the upper left you see a triangle. That represents an antenna, in this case it is a UHF (70 cm band) omnidirectional antenna installed at the top of a 60' tower. The component just below this is a duplexer. It allows us to connect two radios to an antenna at the same time, in this case a receiver and a transmitter. If we attempted to do this with a simple "T" connection the transmitter power would, at best, swamp the receiver. Chances are it would smoke the receiver as the input of a receiver is delicate and sensitive, it is not built to absorb power. The duplexer is a filter that keeps energy intended for one radio from going down the wrong path and interfering with the other radio. As you can see from the arrows, energy from the antenna comes through the side of the duplexer tuned to 449.075 MHz and into the receiver. Energy on 444.075 MHz from the transmitter goes up and out the antenna. The"bottom line" here, what you really need to know, is that the duplexer allows the transmitter and receiver to operate using a single antenna at the same time.
Below the duplexer, and connected to it, is the Vertex VXR-7000. All by itself this radio can function as a self-contained repeater, complete with a built in controller. If we used it in this way you could ignore everything else in the drawing. Anything heard by the receiver on 449.075 MHz would be sent out the transmitter on 444.075 MHz. Viola, a repeater. Look over to the right of the drawing. You see the same thing but in VHF. So we could have a VHF VXR-7000 sitting there doing the same thing. For most of you, the way you operate, that would satisfy your basic craving for repeater operation.
We aren't using it that way however. We operate the VXR-7000 in "base station" mode which disables the built in repeater function and allows us to connect the receiver and transmitter independently to the repeater controller. Again, look at the direction of the arrows making the connections between the VXR-7000 and the RLC-3.
As I said, the Vertex radios can be used as full functioning self-contained repeaters just as they come from the factory. So why would we use an external repeater controller? Well, I'm glad you asked. You see, that's where the power comes in....the power to do great things. Our particular repeater controller, the RLC-3, is a special computer device that does a whole lot of audio switching and mixing as well as various timing and control functions. Think of it as a programmable computer that works with audio. It's important that you understand that it works with audio....it doesn't care if that audio connects to a radio, phone line, MP3 Player, computer or anything else. Below is a photo of an RLC-3 with it's cover off.
Notice on our block diagram that the UHF VXR-7000 is connected to port 1. That is to say that the UHF receiver is connected to receive port 1 and the transmitter is connected to transmit port 1. There is a reason I say it that way and you will come to understand this soon. Anyway, the radio ports are the cards to the left of the unit in the photo above.
We could program the RLC-3 so that anything it hears on RX Port 1 gets sent out TX Port 1. If we do this we then have a basic repeater. Of course we could have accomplished the same thing for a lot less money by using the internal controller in the VXR-7000.
We can also program the controller to send anything it hears on RX Port 2 to TX Port 2. If that's all we tell the controller to do then, based on our block diagram above, we will have a UHF repeater and a VHF repeater. Each will function independently.
But the RLC-3 is a very capable device and it can send audio from any receive port to any transmit port, even to/from multiple ports at the same time. So imagine that we modify our program so that anything heard on RX Port 1 is sent to both TX Port 1 and, at the same time, TX Port 2. If we do that then anyone talking on UHF will not only be repeated on UHF, they will be heard on VHF as well. If we also modify the programming so that RX Port 2 is sent to TX Port 2 and TX Port 1......well now....now we have a UHF repeater and a VHF repeater and the two of them are linked together.
That is how we normally operate by default. On any given day you use either the 145.230 or the 444.075 repeaters without even thinking about them being connected. You think nothing of it. It just works. The audio sounds great. Of course the audio is outstanding because we've kept it all right there in one box and molested it very little as we routed it where we want.
Hopefully by now you can imagine that you can do much more with this repeater controller. What if there was a third radio attached to the controller and it connected to an IRLP node? What if a forth radio was connected and it was a link to a repeater system at another location? These things are possible with what we have.