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For use in Sysop mode, your transceiver connects to a hardware interface, which in turn connects to your computer's sound card and serial port. 

Audio from the receiver goes to the interface board or your sound card's line-in jack, and audio from the sound card's speaker out (or line out) goes through an attenuator to your transmitter's microphone input.  (The attenuator is needed to reduce the sound card output to microphone level).  If your rig has a line-in connection, sometimes available on a back-panel accessory jack, you can usually connect the sound card output directly to line-in. 

Interface Types

Two types of interface boards are supported by EchoLink:

ASCII-controlled:  This type of interface, which is specifically designed for EchoLink, accepts ASCII commands from the computer over its serial port.  These commands key and un-key the transmitter, and request information about incoming DTMF digits.  High-quality boards of this type are available in kit and assembled form from WB2REM or VA3TO.  Details of the original WB2REM circuit were also described in QST for March, 2002. 

Direct-controlled:  This type of interface, which is commonly used for PSK31 and other digital modes, keys the transmitter in response to signals over the serial port's RTS or DTR pins.  The interface usually includes an attenuator to simplify the connection between the computer's sound card and the transceiver's mic jack.  This type of interface may be the best choice if you intend to use digital modes in addition to EchoLink, or if your set-up requires additional isolation between the computer and the transceiver.  The interface does not include a DTMF decoder, but EchoLink's internal decoder may be used instead.  The RIGblaster from West Mountain Radio is an example of this type.

Carrier Detect

In Sysop mode, EchoLink needs some way of knowing when there is activity on the local receiver.  The most common way is to use EchoLink's built-in VOX (voice-operated switch).  The VOX monitors incoming audio from the receiver.  When properly adjusted, the VOX will trigger only when a station is being heard over the receiver.  One advantage of using VOX is that no other connections between the receiver and the PC are required.

VOX is particularly useful when EchoLink is connected to a transceiver which is monitoring the output frequency of a repeater.  The VOX will trigger only when a station is actually speaking through the repeater, and will not generally respond to the repeater's "tail", which could be as long as 10 seconds after each transmission.

However, VOX is not completely reliable, since it is unable to detect a dead carrier.  Also, it introduces an additional delay of a second or so after each transmission.  To help circumvent these issues, EchoLink also supports a direct connection between the receiver and the computer's serial port for positive carrier detect.   This type of connection is especially useful for simplex links.

Many transceivers have a back-panel connection (called "busy" or "carrier detect") which tracks the squelch circuit directly.  This can be wired to the CD, DSR, or CTS pin of the PC's serial port, and EchoLink can be configured to respond to it instead of using VOX.  Typically, this connection must be made through a simple interface, such as a one-transistor circuit.  The circuit should drive the CD, DSR, or CTS pin high (+5V or above) when the squelch is open, and low (0V or below) when it is closed.  Several versions of the interface products mentioned above also support this feature; check the product literature for details.

To enable this feature, choose Sysop Settings from the Tools menu, select the RX Control tab, and choose Serial CD, Serial CTS, or Serial DSR.

Repeater Linking Tips

One of EchoLink's strengths is its ability to link any number of repeaters to each other, or to simplex stations. Here are some tips for setting up and configuring EchoLink to be used as a link to a local repeater.

Remote or Hard-Wired?

There are two ways a repeater can be connected to EchoLink.

With the "hard-wired" approach, the PC on which EchoLink runs is co-located with the repeater controller, and interfaced directly to it, with no additional RF hardware. This allows positive carrier and PTT control between the repeater controller and EchoLink, and eliminates extra "hops" in the audio chain. It also eliminates the need to ID a link transmitter. One disadvantage of this technique, however, is that it requires reliable Internet access at the repeater site, which may be in a remote location.

With the "remote-link" approach, an FM transceiver is connected to the EchoLink PC at a convenient location in range of the repeater, and tuned to the frequency pair of the repeater. In this configuration, the transceiver behaves very much like an ordinary local repeater user, transmitting on the repeater's input frequency (on behalf of EchoLink users) and receiving on the repeater's output frequency. Although this allows the EchoLink equipment to be placed in a more convenient location, it presents some challenges with respect to RX control.

With either approach, EchoLink should be configured with a callsign with a -R suffix, to indicate that the node is a gateway to a repeater, rather than a simplex frequency. If a remote link is being used, the software should be configured to identify itself on the air with the host station's callsign, which is not necessarily the same as the EchoLink callsign (or the callsign of the repeater). Since the link itself is not a repeater, a suffix such as /R in the ID is usually not appropriate (for U.S. stations).

Carrier Detect

One of the most important considerations for an EchoLink repeater node is the method of detecting the presence of a local RF signal. Although the best approach is usually to wire a COS signal into the COM port of the PC, it is often necessary (or desirable) to use VOX instead. Several techniques are described below.

COS from Repeater Receiver: If the node is hard-wired to the repeater controller, the best source of carrier detect is the COS output from the repeater receiver itself -- or an equivalent signal from the repeater controller. This ensures that EchoLink transmits to the Internet only when a signal is being received on the input. Also, the audio connection to the sound card should come from the receiver's audio output, rather than the repeater transmitter's audio path.

COS from Link Transceiver: If the node is remotely located, it may be desirable to use the COS signal from the link transceiver -- but only if the repeater's "tail" is extremely short. Otherwise, EchoLink will keep transmitting to the Internet 5 to 10 seconds after the local user finishes a transmission, severely interrupting the flow of a QSO. Some repeater-node operators have successfully incorporated DTMF tones in their custom Connect and Disconnect announcements to automatically shorten the repeater's "tail" while an EchoLink station is connected, on repeaters which support this type of remote command.

VOX: If the node is remotely located, but the repeater's "tail" cannot be shortened, VOX can be used. When properly adjusted, EchoLink will detect voice signals coming through the repeater, but ignore other incidentals such as the "tail", the courtesy tone, and the squelch crash at the end. This is very important when two repeaters are linked to each other, to prevent endless ping-ponging of one repeater bringing up the other. Here are some tips for adjusting the VOX for use with a repeater:

  1. Set the VOX threshold carefully. (This is the horizontal slider below the audio-level indicator.) The VOX threshold should be set just above the audio level of the repeater's dead carrier, so that it "trips" on voices, but not on the repeater's tail. Watch the purple SIG annunciator while adjusting the VOX threshold.
  2. If necessary, adjust the VOX delay. The default value of 1200 ms is appropriate in most situations. (If you decide to change the value, type it in directly, rather than using the up-down buttons.)
  3. Use the "Smart VOX" feature. This is enabled by checking the "Squelch Crash Anti-Trip" box on the RX Ctrl tab. When this feature is enabled, EchoLink's VOX will ignore short noise bursts, such as the repeater's courtesy tone and the squelch crash when the repeater's carrier drops. Set the time constant to a value slightly higher than the longer of these two signals. Typical settings are 250 ms for a repeater with a (short) courtesy tone, or 80 ms for a repeater with no courtesy tone. Note that the Smart VOX feature does not necessarily suppress these signals in the audio path, it merely prevents them from triggering (or holding open) the VOX.
  4. Anti-Thump: Use the Anti-Thump feature if the squelch crash, as heard over the repeater when your transceiver stops transmitting, seems to be triggering the VOX. Start with a low value and move it gradually higher until the SIG indicator no longer appears when your link stops transmitting.

When the VOX is properly adjusted, the "acid test" is to connect the link to the *ECHOTEST* conference server. After hearing the initial welcome message from the test server, the repeater should drop normally and then remain idle. If the repeater continues to be keyed up by responses from the test server, re-check the above settings.

When the settings are correct at both ends of a repeater-to-repeater link, both repeaters should remain idle except during an actual QSO, or while either repeater sends its ID.

CTCSS Control: If the node is remotely located, this may be the best technique of all -- but it requires cooperation from the repeater. In this set-up, the repeater transmits a CTCSS (a.k.a. PL) tone only while its receiver's COS is active; that is, only while a station is transmitting. The EchoLink transceiver is configured to open up only when this tone is received. The advantage of this system is that EchoLink triggers only on a true signal, and ignores incidentals such as courtesy tones and CW IDs. The disadvantage is that most PL-guarded repeaters transmit a continuous tone, even when no signal is present on the input, so it may require configuration changes to the repeater itself. (Note that this technique can be used whether or a not a PL is required to activate the repeater.)

 

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