ROS VLF 0.8
and 0.4
Baud
Outline
Based on the ROS MF- 1 and MF-7 narrow band data modes , ROS VLF is a free running live key board qso mode , not requiring internet connection or
accurate time or frequency control ,
AFC of 78 Hz is provided for receive and once locked , the overall circuit stability must exceed 5 Hz during the tx
period.
Configured
for operation within the 8 KHz experimental band , using phase continuous multi tone frequency shift keying , with in a bandwidth of
25 Hz , allowing for a system Q of over 300 with out degradation and may be
transmitted using non linear amplifiers.
Provision is
made for the drive frequency division, inherent in some Class E/D amplifiers, by the ability to select ?normal or ? Class E/D? , this selection causes the transmit tones and modulation bandwidth to be
multiplied by a factor of
-2- to 16K / 50Hz , thus after amplification , the signal is reverted to 8k / 25 Hz
Rx frequency is
fixed and not affected by the Tx select function
All normal functions are retained, including the ROS-Chat , allowing text messages to be
broadcast to ?all? or
individual ROS users, via the internet . The Beacon timer cpu and Rx
monitor?s have been disabled to facilitate tx only operation. If connected to the www, reception reports will be uploaded to :-
http://pskreporter.info/pskmap.html
As in MF , spots
will show as band ?unknown?
The system utilises the soundcard to produce in effect a SDR radio operating at 8KHz . it is estimated that the 0.4 baud version will give a noise floor of
some -38 dB , the 0.4 baud version , produces a
higher CPU load than 0.8 , showing round 20% on a dual core lap-top
Data summery
Frequency tx/rx
8950-8975 Hz
Bandwidth
25 Hz
Baud rate
fixed 0.4 / 0.8
Rx
AFC range
78 Hz
Drift
tolerance
5 Hz
S/N 0.4 Baud
-38 dB
Two exe files are available , one
0.4 band , the other 0.8 baud. for
testing
73 - G ..
