VOX
If you want to use VOX (Voice Operated Transmission) then set this parameter to ENABLE. Any
incoming audio from the PC will then operate the Transmit/Receive switch and be transmitted.
When the audio stops, QDX will switch back to Receive automatically. The problem with this is
that any system sounds on your PC, if the PC is configured to deliver these to the QDX USB
sound card, will operate the transmitter and be transmitted.
The default setting “DISABLE” requires a CAT command from the PC host application (WSJT-X
for example) in order to enable the transmitter. This is discussed in this manual in the operating
manual section, on setting up WSJT-X for QDX.
If you wish to use software that does not support CAT Transmit/Receive switching, this may be
one reason why you would want to enable VOX.
If using VOX, you will also need to disable the CAT timeout feature (see below).
Rise threshold
This is a percentage signal level of maximum, above which the transmitter will be keyed down
(switched on). Its purpose is to ignore very low amplitude audio signals at the start of a raised
cosine keying envelope, whose audio tone could be decoded inaccurately due to quantization
error. This is discussed further in the Design section of this manual in the Audio Frequency
Analysis section. The default value of 80% should be fine for all purposes. The value should not
be set too close to 99%, since higher frequency audio where the number of samples per cycle is
small, may not contain a value sufficient to trigger this threshold in every cycle.
Fall threshold
This is a percentage signal level of maximum, below which the transmitter will be keyed up
(switched off). Its purpose is to ignore very low amplitude audio signals at the end of a raised
cosine keying envelope, whose audio tone could be decoded inaccurately due to quantization
error. This is discussed further in the Design section of this manual in the Audio Frequency
Analysis section. The default value of 60% should be fine for all purposes. The value should not
exceed (or be close to) the Rise threshold parameter, otherwise the transmitter will be repeatedly
keyed on and off falsely.
Minimum cycles
This parameter specifies the minimum number of audio cycles to use, in the measurement of
audio cycle period, for audio frequency calculation. This parameter is used in conjunction with the
Minimum samples parameter: both conditions must be satisfied in order for an audio frequency
measurement to be completed. This parameter is discussed further in the Design section of this
manual in the Audio Frequency Analysis section. The default value of 1 should be fine for all
purposes.
Minimum samples
This parameter specifies the minimum number of audio samples to use, in the measurement of
audio cycle period, for audio frequency calculation. This parameter is used in conjunction with the
QDX operating manual; firmware 1_04
17
