Fsk & 2 - microHAM microKEYER Manual

The FSK channel is used by the application program to send the FSK keying signal. FSK is used primarily
for RTTY. It is very important to understand the difference between FSK and AFSK.
FSK is a digital (On/Off) signal used in the transceiver to generate a frequency shift. FSK must be
supported by the transceiver (this mode is commonly labeled RTTY or FSK).
AFSK is an analog (audio) signal used to modulate the transceiver for digital modes as RTTY, PSK31,
AMTOR etc. Computer sound card generated AFSK or PSK does not require special transceiver support
and can be applied with LSB, USB or FM modes. Some radios have dedicated modes for AFSK (generally
labeled PKT, DATA, LSB-D or USB-D) with special features.
It is very important to properly adjust the audio drive level of an AFSK system so as to not overdrive the first
transmit audio amplifier stage in the transceiver and produce a wide, distorted signal, full of intermodulation
products. It is important to appreciate that distortion generated at this point due to overdrive CANNOT be
reduced or eliminated by the reduction of the microphone gain control – it is the signal level that must be
adjusted to be about the same as would be expected from a microphone. The microphone gain control then
becomes a form of transmit power control.
An initial indication of proper audio drive level can be seen on the ALC meter of the radio. Provided that
there is NO audio processing in circuit and that the microphone gain control is in its normal operating
position, then, if the ALC does not show or just starts to indicate during transmission, the signal is likely to
be clean. It is also important is to turn off the microphone compressor, ANY transmit audio equalizer, AND
transmit DSP when AFSK is used. DO NOT use any form of digital modulation (sometimes called
"Transmit DSP") with AFSK or PSK. Some transceivers bypass these circuits automatically when signal is
routed to the rear audio jack instead of the microphone jack, but some do not (for example, the TS-850).
If your transceiver supports FSK, use FSK for RTTY whenever possible. It's the only sure way to
get a clean RTTY signal no matter the microphone gain or compressor (processor) settings on
your radio.
When a COM port is assigned in Router but not in the application program (or the application is not
running), Router will indicate the channel is closed.
When an application opens the COM port, Router will indicate the channel is open and display baud rate,
number of data bits, parity and number of stop
bits in use. For example, 45 5N1.5 means: 45
Baud, 5 data bits, no parity, 1.5 stop bits.
The second FSK port is useful when operating
split with radios that have two receivers (e.g., FT-
1000, FT-2000, FT-9000, K3, Orion or IC-7800). The second instance of the RTTY program should specify
"right channel" for its audio source and should be configured to use the 2
NOTE: microKEYER supports only one audio channel. There is no connection between the audio
output from the second receiver and the sound card. To decode audio from the second receiver, it
is necessary to build a small audio isolation network (transformer) and use custom audio
connections.
Radios without a second receiver can use the 2
different decoding algorithm to provide diversity decoding and transmit from either program.
microHAM © 2010 All rights reserved
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FSK & 2 FSK PORTS
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FSK port for a second RTTY program with a
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Edited by Geoff Anderson, G3NPA
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FSK port for its FSK output.