FreeDV GUI can be challenging to set up. The easiest way is to find a friend who has set up FreeDV and get them to help. Alternatively, this section contains several tips to help you get started.
For Receive only operation you just need one sound card; this is a great way to get started.
-For Tx/Rx operation you need two sound cards. One connects to your radio, and one for the operator. The sound card connecting to the radio can be a rig interface device like a Signalink, Rigblaster, your radio's internal USB sound card, or a home brew rig interface.
+For Tx/Rx operation you need two sound cards. One connects to your radio, and one for the operator. The sound card connecting to the radio can be a rig interface device like a Signalink, RIGblaster, your radio's internal USB sound card, or a home brew rig interface.
The second sound card is often a set of USB headphones or your computer's internal sound card.
Start with just a receive only station. You just need the basic sound hardware in your computer, for example a microphone/speaker on your computer.
@@ -87,13 +87,13 @@The Tools - PTT dialog supports three different ways to control PTT on your radio:
Once you have configured PTT, try the Test button.
Serial PTT support is complex. We get many reports that FreeDV PTT doesn't work on a particular radio, but may work fine with other programs such as Fldigi. This is often a mis-match between the serial parameters Hamlib is using with FreeDV and your radio. For example you may have changed the default serial rate on your radio. Carefully check the serial parameters on your radio match those used by FreeDV in the PTT Dialog.
Also see Common Problems section of this manual.
-Hamlib comes with a default serial rate for each radio. If your radio has a different serial rate change the Serial Rate drop down box to match your radio.
When Test is pressed, the "Serial Params" field is populated and displayed. This will help track down any mismatches between Hamlib and your radio.
If you are really stuck, download Hamlib and test your radio's PTT using the command line rigctl program.
FreeDV 700D is sensitive to tuning. To obtain sync you must be within +/- 60Hz of the transmit frequency. This is straightforward with modern radios which are generally accurate to +/-1 Hz, but requires skill and practice when used with older, VFO based radios.
FreeDV 700E was developed in December 2020 using lessons learned from on air operation of 700C and 700D. A variant of 700D, it uses a shorter frame size (80ms) to reduce latency and sync time. It is optimised for fast fading channels channels with up to 4Hz Doppler spread and 6ms delay spread. FreeDV 7000E uses the same 700 bit/s codec as FreeDV 700C and 700D. It requires about 3dB more power than 700D, but can operate reliably on fast fading channels.
-The 700E release also includes optional compression (clipping) of the 700D an 700E transmit waveforms to reduce the Peak to Average Power Ratio to about 4dB. For example a 100W PEP transmitter can be driven to about 40W RMS. This is an improvement of 6dB over previous releases of FreeDV 700D. Before enabling the clipper make sure your transmitter is capable of handling sustained high average power without damage.
+The 700E release also includes optional compression (clipping) of the 700D and 700E transmit waveforms to reduce the Peak to Average Power Ratio to about 4dB. For example a 100W PEP transmitter can be driven to about 40W RMS. This is an improvement of 6dB over previous releases of FreeDV 700D. Before enabling the clipper make sure your transmitter is capable of handling sustained high average power without damage.
Clipping can be enabled via Tools-Options.
On good channels with high SNR clipping may actually reduce the SNR of the received signal. This is intentional - we are adding some pre-distortion in order to increase the RMS power. Forward error correction (FEC) will clean up any errors introduced by clipping, and on poor channels the benefits of increased signal power outweigh the slight reduction in SNR on good channels.
The High Bandwidth option gives better performance on channels where the phase changes quickly, for example fast fading HF channels and the Es'Hail 2 satellite. When unchecked, the phase estimator bandwidth is automatically selected. It starts off high to enable fast sync, then switches to low bandwidth to optimise performance for low SNR HF channels.
The DPSK (differential PSK) checkbox has a similar effect - better performance on High SNR channels where the phase changes rapidly. This option converts the OFDM modem to use differential PSK rather than coherent PSK. DPSK is used by earlier FreeDV modes such as FreeDV 1600. It affects the Tx and Rx side, so both sides must select DPSK.
If you have problems with 700D or 2020 sync even though you have a strong signal - try these option.
+If you have problems with 700D or 2020 sync even though you have a strong signal - try these options.
If you have an interesting test case, for example:
The sample clock offset is the estimated difference between the modulator (tx) and demodulator (rx) sample clocks. For example if the transmit station sound card is sampling at 44000 Hz and the receive station sound card 44001 Hz, the sample clock offset would be ((44000-44001)/44000)*1E6 = 22.7 ppm.
This indicates the symbol timing estimate of the demodulator, in the range of +/- 0.5 of a symbol. With off air signals this will have a saw tooth appearance, as the demod tracks the modulator sample clock. The steeper the slope, the greater the sample clock offset.
+This indicates the symbol timing estimate of the demodulator, in the range of +/- 0.5 of a symbol. With off air signals this will have a sawtooth appearance, as the demod tracks the modulator sample clock. The steeper the slope, the greater the sample clock offset.
These features were added for FreeDV 700D, to help diagnose sound card issues during development.
-Tools - Options dialog:
+Debug FIFO and PortAudio counters: used for debugging audio problems on 700D. During beta testing there were problems with break up in the 700D Tx and Rx audio on Windows.
The PortAudio counters (PortAudio1 and PortAudio2) should not increment when running in Tx or Rx, as this indicates samples are being lost by the sound driver which will lead to sync problems.
The Fifo counter outempty1 counter should not increment during Tx, as this indicates FreeDV is not supplying samples fast enough to the PortAudio drivers. The results will be resyncs at the receiver.
@@ -417,7 +417,7 @@ FMA - Supports FMA extensions using YMM stateThe txThreadPriority checkbox reduces the priority of the main txRx thread in FreeDV which may help the sound driver thread process samples.
The txRxDumpTiming check box dumps timing information to a console that is used for debugging the rx break up problem on 700D. Each number is how many ms the txRxThread took to run.
The txRxDumpTiming check box dumps the number of samples free in the tx FIFO sending samples to the Tx. If this hits zero, your tx audio will break up and the rx will lose sync. Tx audio break up will also occur if you see "outfifo1" being incremented on the "Fifo" line during tx. Try increasing the FifoSize.
-This feature was developed for testing FreeDV 700C. Select the Test Frame Histogram tab on Front Page
Displays BER of each carrier when in "test frame" mode. As each QPSK carrier has 2 bits there are 2*Nc histogram points.
Ideally all carriers will have about the same BER (+/- 20% after 5000 total bit errors), however problems can occur with filtering in the tx path. If one carrier has less power, then it will have a higher BER. The errors in this carrier will tend to dominate overall BER. For example if one carrier is attenuated due to SSB filter ripple in the tx path then the BER on that carrier will be higher. This is bad news for DV.
@@ -428,7 +428,7 @@ FMA - Supports FMA extensions using YMM stateMonitor the error histogram for a few minutes, until you have say 5000 total bit errors. You have a problem if the BER of any carrier is more than 20% different from the rest.
A typical issue will be one carrier at 1.0 and the others at 0.5, indicating the poorer carrier BER is twice the larger.
Tools - Options - Half Duplex check box
FreeDV GUI can operate in full duplex mode which is useful for development or listening to your own FreeDV signal as only one PC is required. Normal operation is half duplex.
Tx and Rx signals can be looped back via an analog connection between the sound cards.
@@ -440,7 +440,7 @@ FMA - Supports FMA extensions using YMM state - Transmit Tab - To Radio select -> Loopback: Loopback PCM (hw:1,1)