Since version 4.5, Remote SDR offers the possibility of receiving and transmitting messages in RTTY.
Starting RTTY mode
A click in the “Digital” selection box opens a window dedicated to RTTY mode. Then click “Start”. RX Audio must be “On” to view something. The audio level is irrelevant.
On a single page are all the elements to control reception and transmission in RTTY.
In the upper part, the settings, a “waterfall” view of the audio spectrum, the response curve of the filters as well as an XY representation of their outputs.
In the middle part, the result of two detections. One based on amplitude comparison, the other on phase.
In the lower part the zone of the messages to be sent and the macros of the predefined messages.
This zone allows the choice of the baud rate and the frequency offset between the “Mark” and the “Space”. The audio frequency of emission of the Mark can be equal to the reception or predefined.
A checkbox allows to exchange the frequency of the “Mark” and the “Space”.
The selectivity Q of the bandpass filters centered on the “Mark” and the “Space” is adjustable.
It is possible to add a notch filter to eliminate unwanted noise.
Two detection processing are carried out simultaneously. One is based on the comparison of the output amplitudes of the “Mark” and “Space” filters, the other compares the phase rotations.
If we are well calibrated in frequency, the phase comparison proves to be more effective in noise. If one is slightly offset, the amplitude comparison gives better results.
It is possible to display the raw output of the detectors (orange curve) and the decision 1 or 0 (green curve) after filtering on the duration of the bit.
On the side, buttons allow you to force the letter or symbol mode.
The spectral analysis represented in the form of a “waterfall” makes it possible to calibrate the frequency of the 2 filters by a click on the screen or the wheel of the mouse. The red and green curves give the frequency response of the filters set on the “Mark” and the “Space”.
The representation in XY of the output amplitudes of the filters makes it possible to ensure a good setting in frequency when a cross appears instead of a cloud of points.
At the bottom of the page is the text box to send. To simplify typing, there are 16 predefined messages. To modify the title, write on the button. To modify the content, double-click. The callsigns, names and report can be defined by abbreviations which will be replaced by the values defined in the fields.
The transmitted text may or may not appear in the zones of the two detectors. Remember to uncheck the “TX Txt Out” box if you traffic in Full Duplex, so as not to mix up the message sent with that received.
A TX On/Off button launches the HF transmission.