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. Basically a second radio (even a old hand held or mobile rig) is connected to a repeater that you want linked to another and uses that new radio as if it was a regular "users radio" on the other system. This "link" radio need not be duplex because of the way the link and repeaters are configured. Naturally the link (remote base) radio will need to be on the same band, frequency, split, and PL as the repeater you are linking to. Remote Base operations can be carried out on any amateur voice band, even HF! Links below 220 should be used on a part time basis because the FCC says that 'linking' must be done above 222.15 MHz, however Remote Base operation is left to individual and local interpretation.
Commonly, when deploying a link SYSTEM that will be * ON * full time - a repeater on 222.15 MHz. or above in the center of the desired coverage area is designated to be the system "HUB". You can remote base, or "link", as many "outboard" repeaters into the hub as you wish, providing you have a good RF path to the hub from all of the outlying 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. The controller at the outlying sites needs to have 2 ports, one for the repeater and one for the remote base radio.
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/
How a Remote Base works.....
Basically, a Remote Base link is an addition to a normal repeater,
which works like this: the user transmits 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 'hang time' (also called
"carrier delay") on the repeater transmitter; during this time is when
the courtesy tone, if any, is heard and the repeater transmitter drops
after this time (usually 1 to 5 seconds) has expired. A repeater
with a remote base operates the same as any other repeater, except that
it is in three modes: "remote base off" (i.e. repeater is normal), "remote
base receive (or monitor)", and "remote base transmit" (or transcieve).
In the receive or monitor mode the repater listens to two frequencies,
the normal input and also the frequelcy the remote base radio is listening
to. In most cases the courtesy beep is changed so that the listening
user can tell which receiver the signal is coming in on. When the
remote base is in transmit mode the user keys into the repeater on the
input frequency, the controller recognizes the user and keys the repeater
transmitter and the remote base radios transmitter, the user speaks and
their voice is heard not only on the repeater, but also on the remote base
transmitter. 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 remote base trnasmitter drops immediatly while the repeater
transmitter continues to transmit during the 'hang time' as usual.
The instant the remote base radio unkeys it reverts to receive mode and
the remote base user will hear the far end repeater's courtesy beep (if
any). The remote base could just as well be on a simplex frequency,
or even an HF frequency (yes, you can run a 20 meter SSB killowatt using
your 440mhz handheld).
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 during COS/PL]. 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 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 3AT) 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 tower mounted beam or corner reflector for more distant sites. Remember the FCC says linking antennas need to be directional. Some link systems are frequency and band agile, meaning you can select a particular band, frequency, split, PL frequency and even power remotely. The ACC controller company made this type of linking popular with the FC-1 and FC-900 link interfaces. A more modern combination is a NHRC-10 and an Icom 706 which covers 160m through 6m, later models added 2m and 450mhz.
Hopefully by now you see that this type of link system is just like operating a handie or mobile rig while sitting at the repeater site. Only difference is you have the ability to do it while away from the site; anywhere the repeater side of your remote base has coverage.
Another trick: you can have a repeater at a hilltop site, with a 420mhz link back to your house, and operate your HF station at your house as a remote base. it woudl take a two-port controller at the repeater site feeding the link radio, and a controller capable of operating the HF radio at you house controlled by the link radio.
Here are url's to 3 systems, local to me, using this type of linking
system:
http://www.kuggie.com/target
http://www.n8yib.com
http://www.shol.com/kuggie/ahra/hmft.html
Full Duplex?
A different method, commonly used in larger link systems, like those
of the Cactus Intertie (originally based in California but now in many
states), 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 complete repeater (remember it's duplex),
so duplexers are often required along with modified radios that will operate
full duplex for extended duty cycles. The controllers needed for
this type of system are complex and expensive, and implementing this type
of system (correctly) is not an easy task. This type of system *could*
have the links transmitting all the time, but usually doesn't. This
eliminates any 'lag' time for the system to become active, and usually
sounds just a bit better due to running "flat audio" throughout the system.
There are articles on flat audio at this web site.
Here are url's to their systems so I'll not go into trying to explain
them here - again:
http://www.cactus-intertie.org/
http://www.qsl.net/nera/
Internet Linking:
The latest type of linking to hit the amateur scene is via the internet.
IRLP, I-Link, EchoLink, app_rpt - Asterisk, 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.
Here is information on those systems:
IRLP
I-LINK
Echolink
Echolink Boards
app_rpt - Asterisk
The Asterisk app_rpt Project
Page last modified: March 24 2003 @ 8:54 Local Eastern
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