In GSDR exist two options for direct sending I/Q signals sound card output to connect external programs. For now been tested with CW Skimmer program to decode CW signals in a wide frequency range. To start you need to install CW Skimmer and provide license and download the latest update from GSDR address:
First way is using only one audio card for SDR radio with 4 inputs/outputs (2 stereo pairs):
In this case, is used Delta 44 audio card in dual channel mode with 1/2 pair of input/output. Settings are standard for working with the G59 radio. Only difference is the new options in the command group “Direct I/Q output”:
- Enable: enable this function;
- IQ correction: suppress unwanted image signal with fixed values for Phase and Gain;
- RX Shift: indicates how much differs received frequency compared to Si570 local oscillator and must be identical to the value of CW Skimmer program (in the example below is for 24kHz).
In this configuration the reception of signals from input 1/2 passed unprocessed to output 1/2. With slider AF can only be corrected signal level (also does not work WBIR correction). Output 1/2 Delta 44 cards need to be connected to G59 (because it’s used for transmitting) and from the G59 audio output cable to the audio inputs on the card which is connected to CW Skimmer:
In this example is used 3/4 Line input for the Delta 44 sound card and Speakers from HD Realtek Audio (integrated on the motherboard) for decoded audio. It was necessary to set CW Skimmer in SoftRock-IF mode:
Value for Audio IF, Hz must be the same as in GSDR in order to decode and display work correctly!
Finally, it is necessary to setup GSDR CAT connection with CW Skimmer:
You can download virtual com port driver from address: http://sourceforge.net/projects/com0com/
Setting the CAT port of CW Skimmer is a little more complicated and consists of two steps:opening of the CAT and clicking on Configure. Choose COM20 and other parameters set as in GSDR must be identical. For Poll-time recommended value is 250mS which is an interval at which CW Skimmer refreshes the data by sending queries to GSDR (recieved frequency – FA command and the general state – IF command). Time out is the time to wait for a response before sending new one.
If everything is correctly connected after starting GSDR and CW Skimmers you will get the correct picture and sounds of decoded signals:
Here is a VFOA 14.014270 MHz for 24kHz LOSC lower. On CW Skimmer screen signals are visible coming from the G59 output in the range of 14006-14022 Mhz. Receiving filter width has no effect because the decoding is performed by CW Skimmer. With the left mouse button is possible to choose a new frequency inside CW Skimmer program and the command will be forwarded to GSDR (sometime with small delay, not yet determined the reason). Change is much faster using the GSDR traditionally.
In this example is used 3/4 input and 1/2 out of 44 in the Delta 44 in two-channel mode. The settings are identical to the primary audio card. Only difference is signal level control: it is used RX Gain (in the upper right corner). Due to the nature of VAC software little delay is present because data passes through the Ring buffer. It is best for the Sample Rate value to be identical to primary audio card to avoid resempling
(additional CPU time and losses in the signal dynamics).
Goran Radivojevic YT7PWR