Sound Card Interfacing (updated 8/25/09)

There are many sound card interfaces out on the market today and most should be able to be utilized with RoMac 10 Band Equalizer & Receive Filtering software.

There are a few terms that one should become familiar with before we delve into the nitty-gritty of hooking up an interface for use with the Equalizer software. First lets tackle the serial port.  There are a few signals on the serial port that we are interested in. To key your interface you can use either the RTS, DTR or both signals. The default is RTS. You may configure the signal line to use in the Setup->Settings->Serial port dialog.  This signal originates from the computer (software) to the soundcard interface unit. When sent, places the radio in the transmit mode.  If your present sound card interface and digital software places your transceiver in the transmit mode, so far so good.

The other signal on the serial port that is needed to utilize all features of the Equalizer software is the "CTS" or the "DSR" signal. The default is CTS, which most sound card interface's utilize. This signal originates from the sound card interface to the computer. This signal tells the software that the transceiver is in the transmit mode (actually that the sound card interface has been placed into the transmit mode). Most sound card interface units that utilize the "RTS" or DTR signal to place the transceiver into transmit, will supply this signal, when the PTT switch is activated (closed). This signal is only required for "Rig Interface Mode" and certain modes of the CW I'der.

See Help File for more information on using the Rig Interface Mode (Under Serial Port settings).

If you going to use the 10 Band Equalizer for just equalizing your transmit audio the interface does not need to have the CTS and/or DSR signal.

If your present sound card interface works with some kind of digital mode software, you may be assured that the Equalizer software will work correctly in both transmit and receive.

Commercially made sound card interface units route the sound cards "Line Out" (speakers) and "Line In" audio paths correctly. After all if they didn't, they wouldn't work with all the digital software on today's market.

Some of the higher end sound card interface units also take care of routing the microphone audio correctly. If your interface unit has the capability of routing your microphone audio to the "microphone in" on the sound card you're all set, although I prefer to wire the microphone directly to the sound card in order to avoid any frequency restricting transformers that may be in line when using an interface unit.

Please note that some interface face units use an inexpensive audio isolation transformer that may have an effect on the audio pass band.  In those cases you are better off connecting your microphone directly to the sound card. Cabling your microphone directly to you sound card and using a ferrite core (type-43 or type 31), may also help reduce any RF on your audio. See FAQ #3 for more information.

If your sound card interface doesn't have this capability, simply cable the microphone directly to the sound cards "Microphone Input" (use stereo jack, ground to sleeve, hot side to tip, leave the ring not connected. Balance microphones should be wired hot to tip, minus and shield to sleeve, and ring left unconnected. See FAQ #13 for microphone wiring issues) and leave all other cabling as outlined in the sound cards interface units documentation. 

Most sound card interface units that we have looked at, that have some kind of PTT arrangement, will supply the correct serial port signals for our software to function correctly

Click here  for a simple to build interface unit that supports all modes of the RoMac 10 Band EQ and Receive Filtering. 

The RoMac 10 band Equalizer and Receive Filtering software has five different modes of operation. The table below outlines the serial port requirement  for each, and which features of the software may be utilized. The software utilizes the "microphone in" for transmit audio and the "line in" for receive audio. The sound cards "line out" (speakers) is utilized for either audio to the transmitter  for the transmit EQ, or to the speakers for receive filtering. See FAQ #18 for more information....

Software PTT Mode

Serial Port Requirements

Software Features Available

"Xmit Only" None Transmit Equalizer Only.
"Space Bar (Spc Bar)"
Software controls radio
RTS or DTR Signal to Key Radio via interface or CAT commands. Transmit EQ, Receive Filtering and CW I'der. Push to talk only from software with space bar.
"Noise Gate"
Software controls radio.
RTS or DTR Signal to Key Radio via interface, or CAT commands. Transmit EQ and CW I'der. Acts like Vox. When noise gate opens, software keys transceiver.
"Rig Interface"
Rig Interface controls software and Radio.
RTS or DTR to key radio via interface and CTS or DSR from rig interface to set TX/RX in software.

Not available when using CAT commands. (Disabled)
All features available, transmit EQ, receive filtering, and CW I'der. PTT from rig interface switches software between transmit EQ and receive filtering, and keys radio.
Receive Only None Receive Filtering

CW Identifier Serial Port Requirements
(In Addition or with Serial Port Requirements Outlined above)

Key on Time RTS or DTR to Key Radio via interface, or CAT commands
Key Next Xmit CTS or DSR from Rig Interface and RTS or DTR to Key Radio via interface, or CAT commands
Key Every Xmit CTS or DSR from Rig Interface and RTS or DTR to Key Radio via interface, or CAT commands
Click on Status RTS or DTR  to Key Radio via interface, or CAT commands
Disabled None

Using CAT Commands to and from radio. (No sound card interface - Audio routed directly to radio)

If using CAT commands and the radio supports a command to ask the radio if its in transmit or receive all modes except the "Rig Interface" are operational. "Space Bar" and "Noise Gate" modes available only from equalizer software. All CW I'der modes are operational. Click here for more information...
Keying Radio and/or Sound Card Interface via CAT program.
All modes of CW I'der operational. "Xmit Only" and "Rig Interface" available when keying from CAT program. "Space Bar" and "Noise" gate available from equalizer software. With this option selected, keying from the radio and/or sound card interface is also available. Although the "Rig Interface" mode is available, the software can not develop the proper delay, if keying from the radio.(CAT commands enabled).