R1.1
Copyright © 2016 SDRplay Limited
20
SDRuno User Manual
8. External converter offset
Up to four converter offsets can be stored in each instance of SDRuno. Offset settings are available in
Main window->Sett.->OFFSET.
8.1 Changing a converter frequency offset
Enter the new frequency in the edit box to the left of the relative button then press the ENTER key.
8.2 Enabling a converter offset
Click on the relative offset button.
8.3 Disable active offset
Click on the
NONE
button.
8.4 Inverted spectrum mode
Some converter is designed so that its LO frequency is greater than the input signal frequency; because
of this the output spectrum is inverted. In such case the inverted spectrum mode must be activated,
clicking the INV button. Also the I and Q channels must be swapped (Main window->OPT->Swap I and Q
Channels).
9. CAT
CAT control has been around for at least 25 years so it is a well-known technology: there is no need to
review the basics here but a little refresh may be useful to understand how CAT has been implemented in
SDRuno.
Whatever CAT protocol we choose, there is always a controlling device and a controlled one. In origin
controlling devices were PCs and controlled devices were physical radios (receivers or transceivers) and
accessories (rotors, switches, amplifiers etc.). Physical communication ports (serial ports for example)
were used for the data exchange.
Per definition, in a CAT session only the controlling device can initiate a transaction. For example, the PC
might send a “give me the VFO A frequency” while the radio might reply “the VFO A frequency is 3561230
Hz”.
The logical roles can’t be exchanged.
Now that we have software radios (like SDRuno) a CAT session can be no more necessarily only between
a program inside a PC and an external device but can be also between different programs inside the
same PC (and even in different PCs).
In order to achieve this we need a way to interconnect programs; one common solution is using special
software tools to create “virtual com ports” pairs interconnected with “virtual null modem” cables. Then
applications can see the virtual com ports as real ones, using them for communication. More on virtual
ports later.
Another requirement we need is that the software radio must “impersonate” a controlled device and react
the same.
