General notes
micro Keyer provides extensive flexibility in routing audio among the computer sound card, transceiver, and station microphone.  This allows customizing the audio configuration to meet the needs of a specific software program and operator requirements for particular operating mode.
 
From transceiver through micro KEYER to the computer.
micro Keyer always routes audio from the transceiver to the computer sound card; operation is "What you hear is what you get."  Receive audio (including monitor audio and sidetone if the transceiver supports it) goes to the computer SOUND CARD LINE IN.  This allows real time decoding of digital modes (RTTY, PSK31, etc.) and/or recording the received audio directly to a computer file. 

An audio cable must be connected from the micro KEYER SOUND CARD IN jack to the computer SOUND CARD LINE IN.  If the computer does not have a LINE input, the MICROPHONE input can be used but the micro KEYER end of the cable must remain plugged in to the IN jack.
 
From computer through micro KEYER to the transceiver.
Audio generated by the computer can be used for several purposes.  For example, it can be used as memory voice keyer in voce modes (SSB, AM, FM), or for modulation of digital modes (AFSK/RTTY, PSK31, MFSK, etc.).  The micro KEYER provides three audio routing settings: Setting A disconnects the computer audio and connects the microphone to the transceiver microphone input; Setting B routes the computer audio to the transceiver rear panel audio input (PKT or AUX depending on manufacturer); Setting C routes the computer audio to the transceiver microphone input.  Since the PKT or AUX input of most radios bypasses the microphone preamp and other audio processing stages which can distort digital modulation generated by the sound card, Setting B is recommended for digital mode operation.
 
An audio cable must be connected from the micro KEYER SOUND CARD OUT jack to the computer SOUND CARD LINE OUT or HEADPHONES jack.
 
From station microphone to the computer or to the transceiver.
A microphone which matches the pinout of your radio should be attached to the micro KEYER RJ45 connector.  If the transceiver and microphone are terminated with circular 8 pin FOSTER connector, the (optional) cable set contains an adapter.  Heil microphones can be used directly by plugging them into the EXT MIC jack located on the rear panel of micro KEYER.  Setting A connects the station microphone to the transceiver microphone jack.  Setting B or C connects the station microphone to the computer SOUND CARD MIC IN. 
 
When the station microphone is connected to the SOUND CARD MIC IN, an optional pre-amplifier can be enabled by moving two internal jumpers to the second position.  The sound card microphone input is usually not sensitive enough for low level dynamic microphones (like the Heil elements) and the preamplifier needed to provide sufficient drive for sound card operation.
 
An audio cable must be connected from the micro KEYER SOUND CARD MIC jack to the computer SOUND CARD MIC IN jack.
Audio routing depends on three possible routing settings A - B - C in USB Device Router program as well as the method and source of T/R (transmit/receive) keying.
 
These settings are applied when transceiver is in receive mode or keyed by the internal VOX circuits.
 
A - This setting disconnects computer generated audio from the transceiver and connects the station microphone to the radio.  This setting is useful for those who operate SSB with VOX and do not want the transceiver triggered by sounds generated by the computer.
 
B - This setting routes audio from the computer sound card output to the transceiver rear audio input and connects station microphone to the sound card mic input.  This setting is useful for those who operate digital modes with VOX control.
 
C - This setting routes audio from the computer sound card output to the transceiver microphone input and connects station microphone to the sound card mic input.  This setting is useful for SSB operation with VOX or PTT and software (for example: WriteLog) which is able to route microphone audio thru the sound card.
 
These settings are applied when the transceiver is keyed by a computer generated PTT signal (on a virtual serial port) or by WinKey PTT.
 
A - This setting disconnects computer generated audio from the transceiver and connects the station microphone to the radio.  This setting can be used for CW or FSK mode and is useless for SSB or digital mode operation.
 
B - This setting routes audio from the computer sound card output to the transceiver rear audio input and connects the station microphone to the sound card mic input.  This setting is useful for digital mode operation when the computer generates a PTT keying signal on a COM port.  This is the preferred setting for digital mode operation.
 
C - This setting routes audio from the computer sound card output to the transceiver microphone input and connects the station microphone to the sound card mic input.  This setting is useful for SSB message (“voice keyer”) playback and recording with software capable of providing a PTT signal on a serial port.  This is the preferred setting for SSB contest operation using WriteLog or the N1MM Free Contest Logger.
 
This setting is applied when transceiver is keyed by the microphone PTT or a footswitch attached to the Footswitch jack on the back of the micro KEYER.
 
A - This setting disconnects computer generated audio from the transceiver and connects the station microphone to the radio.  This setting is very useful for SSB when is required to have microphone connected directly to the transceiver and stop a message in progress without hitting keyboard Esc key first.
 
B - This setting routes audio from the computer sound card output to the transceiver rear audio input and connects station microphone to the sound card microphone input.  This setting is useful for digital mode operation when the computer does not provide a PTT keying signal and you wish to have T/R switching fully under control by footswitch and not by VOX.
 
C - This setting routes audio from the computer sound card output to the transceiver microphone input and connects station microphone to the sound card microphone input.  This setting is useful for SSB operation when computer does not generate a PTT keying signal and you wish to control T/R switching manually by footswitch.
 

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