Connecting a Transceiver

The most common EchoStation configuration is to connect an FM transceiver to the sound card and COM port of your PC.  This configuration can be used either as a simplex repeater or as an announcement machine, since it is not necessary in either of those modes to transmit and receive simultaneously.

The three connections should be made as follows:

  • Transceiver to Sound Card (Receive Audio)
  • Sound Card to Transceiver (Transmit Audio)
  • COM Port to Transceiver (PTT Control)
  • Receiver to COM Port (Carrier Detect; optional)

These connections are described in detail below.

Transceiver to Sound Card (Receive Audio)

This is usually a simple matter of running a shielded audio cable from the radio's speaker jack (or "line out" jack) to the Line In connector on the sound card.  If you are unsure which connector on the sound card is Line In, consult the documentation that came with the sound card.

In some cases, the Line Out (or Rec Out) signal from the radio is not strong enough to be used with the sound card's Line In connector.  The Microphone In connector can usually be used instead.  In either case, be sure the sound card software's Recording control is set up to receive audio on the connector being used.

Sound Card to Transceiver (Transmit Audio)

If the transceiver has a Line In connector, a shielded audio cable can be run directly from the sound card's Line Out connector to the radio's Line In connector.  Otherwise, it is necessary to connect to the radio's microphone connector using an attenuating cable, or a cable with an attenuator connected.  This prevents the radio's microphone circuit from becoming over-driven.  10 to 20 dB of attenuation is usually needed.

If an interface device such as the RIGBlaster is used, the correct attenuator is built-in.  All that is necessary is to connect a shielded cable between the sound card's Line Out connector and the RIGBlaster's Line In connector, and to plug the RIGBlaster's microphone cable into the radio.

COM Port to Transceiver (PTT Control)

In most cases, it is necessary to wire the PC's COM port to the radio's push-to-talk circuit, to allow the computer to turn the transmitter on and off.  (If the radio supports VOX, this connection can sometimes be omitted).

EchoStation uses the COM port's RTS and/or DTR pins to control the transmitter.  The program asserts the pin(s) to switch the transmitter on, and drops the pin(s) to switch it off.  The specific COM port to be used, and the choice of RTS and/or DTR, is selectable on the Transmitter tab of System Setup .

The PTT circuit in most radios "floats" high during receive, and is grounded to begin transmitting.  A simple one-transistor switching circuit can be used to connect the COM port to this type of radio.

If an interface device such as the RIGBlaster  is used, the PTT switching circuit is built-in.  All that is necessary is to connect a standard serial cable between the computer's COM port and the connector on the back of the RIGBlaster, and to plug the RIGBlaster's microphone cable into the radio.  The choice of RTS or DTR has no effect since the RIGBlaster responds to either.

Receiver to COM Port (Carrier Detect; optional)

EchoStation must be able to detect whether the receiver is squelched (not receiving a signal), or un-squelched (receiving a signal).  In most cases, the VOX capability built in to EchoStation is adequate for this purpose.

However, in some cases, it is desirable to rely upon a direct connection between the receiver and the PC, rather than using VOX.  This arrangement can make the program more reliable with very quiet receivers, where a silent full-quieting transmission has approximately the same audio level as a squelched receiver.  It also avoids the need for setting the VOX level precisely.  This connection is also required for running EchoStation in Simplex Autopatch mode.

If the transceiver (or receiver) has a "channel busy" or "carrier detect" connection, often available on the back-panel accessory connector, it can be wired to the CD, DSR, or CTS pin of one of the PC's COM ports for this purpose.  The specific COM port and pin to be used is selectable during set-up and configuration, and can even be shared with the PTT function, with the appropriate cabling.  For configuration information, see System Setup .

If COM port carrier-detect is enabled in EchoStation, the program monitors the CD pin of the selected serial port, and considers the channel "busy" when the pin is asserted (high), and "squelched" when the pin is dropped (low, or negative).  A simple interface circuit can be built which drives this RS-232 signal with the carrier-detect signal from the radio.

A sample interface circuit is shown below.  The MC1488N chip is available from Radio Shack (276-2520).  The negative supply voltage is "borrowed" from the computer's TD pin.