Amateur Repeater Linking

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by Kevin Custer W3KKC
Maintained by Mike Morris WA6ILQ

The 'best way' to link repeater sites is really dependent on the situation and personal preference, so instead of giving you the 'best' way, I'll give you a few examples of how it can be done and you can decide what it the best for your situation. This article assumes you will be linking amateur repeaters, but the procedures could be followed to link commercial sites as well; assuming you are within the rules of the particular commercial service.

The "Remote Base" type link system is the most common because of its simplicity and low cost. The term "Remote Base" comes from the situation that you are installing a base station that will be controlled remotely. Basically a simplex radio (an old mobile rig or even a handheld with external DC power and an external antenna) is connected to a repeater that you want connected to another. This Remote Base radio need not be duplex because of the way the link and repeaters are configured. The remote base radio will need to be on the same Band, Frequency, Split, and PL as the repeater you are connecting to and will essentially be one more "user" of the destination repeater. Remote Base operations can be carried out on any amateur voice band, even HF! Full Time Links below 2M should be used on a part time basis, however Remote Base operation is left to individual and local interpretation.

The remote base linking can be a single destination repeater, or multiple destinations can be set up, with a "hub" system that all the remote bases talk to. Think of the remote bases as "spokes" to the "hub.

Commonly, when deploying a FM link SYSTEM that will be * ON * full time - a repeater on 222.15 MHz or above is positioned in the center of the desired coverage area and is designated to be the hub repeater (which is usually on a different band from the "outboard" or "spoke" repeaters).

The hub is the main repeater in the system. You can remote base, or "link", as many "outboard" or "spoke" repeaters into the hub as you wish, providing you have a good RF path to the hub from each of the outboard repeater site(s). All ID's from the hub are heard through the entire system, so if you like voice ID's, they need only exist on the hub. Since you can disconnect or "un-link" any repeater from the system, all outboard repeaters should have their own controller with ID. This controller needs to have 2 ports, one for the repeater and one for the remote base radio.

The controller needs to be programmed to provide "remote base off", "remote base monitor" and "remote base transcieve" functions. In "monitor" mode the local repeater is listening to the "hub", but not transmitting to it. In "transcieve" mode it is. The repeater controllers at the spoke sites are programmed to come up in "remote base monitor" mode after any power outage or reset.

The NHRC controller company (and several others) make a few models of controllers that have remote base link capability.

Here are a few I have worked with before:
http://www.nhrc.net/nhrc-4/
http://www.nhrc.net/nhrc-5/
http://www.nhrc.net/nhrc-6/
http://www.nhrc.net/nhrc-10/

The Scom 7K is also an excellent choice, it's port #1 is a full repeater, the Port #2 is easily configured as the remote base. The receive-only port #3 is ideal as a control receiver or as a weather receiver.
The Scom 7330 is a full 3-port controller with 9 receive-to-transmit paths.

How a Remote Base works.....
Basically, a Remote Base link works like this: A repeater with a remote base operates the same as any other repeater; the user keys into the repeater on the input frequency, the controller recognizes the user and keys the repeater transmitter. Audio from the repeater receiver is transferred into the repeater transmitter, and the user is heard on the repeaters output frequency. When the user unkeys, the controller usually puts some "carrier delay" or "hang time" on the repeater transmitter; during this time is when the courtesy tone is heard (if there is one) and the repeater transmitter drops after this time (usually 1 to 5 seconds) has expired. When a remote base is connected and in transcieve mode the user keys into the repeater on the input frequency, the controller recognizes the user and keys the repeater transmitter, at this same instant the controller also keys the remote base radio, the user speaks and their voice is heard and not only transmitted over the repeater, but also the remote base transmitter frequency. If the remote base is dialed on a repeater frequency, the users voice is heard on the linked repeater also. When the user unkeys, the repeater transmitter continues to transmit during the 'hang time', however, at this instant the remote base radio unkeys and starts receiving. The remote base could just as well be on a simplex frequency, or even an SSB HF frequency.

With this type of link, the remote base transmitter is only "on the air" when the user is transmitting; thus the link transmitter follows the activity of the local user, (i.e. link PTT only while the repeater receiver is unsquelched - no courtesy beep on the remote base transmitter). Activity heard on the remote base receiver makes the controller key the repeater transmitter and this audio is heard over the local repeater transmitter. So, immediately after the user unkeys the audio from the linked repeater is transmitted over the local repeater and you hear its courtesy tone and hang time. Since the remote base transmitter is low power and keyed off and on, its duty cycle is really no more than the user so you don't have to be overly concerned about it burning up because of not being rated for continuous duty.

Many times a handheld radio (like the Icom IC-2-AT (2 meters), IC-3-AT (220 MHz) or IC-4-AT (440 MHz) on low power is plenty good enough to link to another repeater. Remember you are linking one repeater site to another and many times this path is "line of sight". Remote base antennas can range from a simple rubber duck when linking to another local repeater to a roof-mounted or tower mounted beam or corner reflector for more distant sites. Remember the FCC says linking antennas need to be directional. Many link antenans are horizontally polarized just to minimize the space occupied on the roof or tower. Horizonal polarization also delivers several dB of free isolation from the vertical repeater antenna(s). Some link systems are frequency and band agile, meaning you can select a particular band, frequency, split, PL frequency and even power remotely. Some even have remotely controllable beam antennas (i.e. you can turn the beam and read back the direction). The ACC controller company made this type of linking popular with the FC-1 and FC-900 link interfaces.

Hopefully by now you see that this type of link system is just like operating a handheld or mobile rig while sitting at the repeater site. Th only difference is you have the ability to do it remotely - while away from the site; anywhere your repeater has coverage.

Here are URL's to 2 systems, local to me, using this type of linking system:
http://www.kuggie.com/target/
http://www.ahra.fm/

Full Duplex
A different method, commonly used in larger link systems, like those of the Cactus Intertie (mostly southwestern USA), NERA, and other larger systems use full duplex radio systems to accomplish their links. This type of system is likely better for full time systems if you can afford it. It's expensive because every link is just like running another repeater (remember it's full duplex), so duplexers (or dual beam antennas with decent physical separation) are often required along with modified radios that will do duplex. The controllers needed for this type of system are complex, multi-port and expensive (if purchased commercially), and implementing this type of system (correctly) is not an easy task. This type of system *could* have the links transmitting all the time. This eliminates any latency or 'lag time' for the system to become active, and usually sounds better due to running "flat audio" throughout the system.

The RLC Club Deluxe 2 can have up to 6 ports and is popular on larger systems.

Here are URLs to their systems so I'll not go into trying to explain them here - again:
http://www.cactus-intertie.org
http://www.neradc.org/

A note on link frequencies:
However you do your point-to-point linking, remember to coordinate your link frequencies with the local coordiators. Many areas use frequencies in the 420-439 MHz range for links, but in some areas these frequencies are not available. In Ohio, for example, links are between 433-434 MHz, and 445-447 MHz due to the "Line A" situation.

Internet Linking:
The latest type of linking to hit the amateur scene is via the Internet. IRLP, I-Link, EchoLink, Allstar and others have shown that the internet is a great way to connect repeaters together that have quite a distance between them (or poor radio path) and have access to a good internet connection at the repeater site.

The big issue is latency - when you key your transmitter and it takes several seconds for the far end system to recognize you.

Here is information on those systems:
AllStar Link
IRLP
http://www.ilinkboards.com/
http://www.synergenics.com/el/
http://www.ilinkboards.com/echolink.html