FreeDV Digital Voice

Last updated on the 1 st February 2013

I have an old Windows XP system for digimodes programs that are hard (if not impossible) to run on Linux - like ROS and the IZ8BLY programs. This describes set-up and operating procedures for freeDV ON MY SYSTEM.
I hope to expand on the content as I myself get more familiar with the program.


If you are using digital modes, you have most of the things required to run freedDV already (TRX, PC, interface). All you have to do to add digital voice - and in particular the freeDV flavour - is the following:

1. Buy yourself a USB sound-"card" plus a headphone/microphone set, often called a "dongle". Sometimes these are integrated (for instance Jaycar AA-2032).

2. Download the software (free), at the moment I use only the Windows version:
URL to download: http://freedv.org/tiki-index.php

3. Install the hardware:
This will be done automatically. Plug in the USB soundcard (dongle). Windows will detect it.

4. Install the software:

Unzip the zip file and put the extracted files in a separate directory (folder):

Dir list

Create a desktop link:
link


You can have freeDV and one or both versions of the old fdmdv on your PC as long as you use separate directories. Of course you can only use one program at any given time!
This is how feeDV looks on RX:
freedv screen

Program Set Up:

Audio - Select Audio Options as follows.

This is an example from my set-up. I have an integrated sound system and a USB dongle. The settings are un-intuitive. To make the program work properly I had to swap the mic and headphone plugs on the USB dongle! There is no right setting of the "Audio Options" if this swap is NOT done. So beware and test thoroughly!

For RX:
RX audio settings

For TX:
freedv audio for TX
For audio level settings, use the Windows mixer:
NOTE THAT THIS IS MORE COMPLICATED THAN THE OLD FDMDV SETTINGS!
RX Input = Mixer for primary soundcard Recording Line-In or Mic-In (connect to receiver's speaker)
TX Output = Mixer for primary soundcard Playback Master Volume AND Wave volume (connect to transmitter's mic input)
Voice input = Mixer for USB Headphone Set Recording Mic-In (connect Headphone mic to USB dongle)
Voice output = Mixer for USB Headphone Set Playback Master Volume (connect Headphomes to USB dongle)
Select ComPort (PTT): Under Settings, click on ComPort, and port number, and then click OK.

Callsign: This is not only the callsign but also additional information that will be displayed on the bottom info window on your
QSO partner's screen. Keep it short: Call, name and QTH (max. 80 characters).

Operating Procedures:

Receiving Digital Voice:
"Waterfall"
is the default display for receive and will switch to "Frm Mic" for monitoring transmit mic audio level.

Tuning must be within a few Hertz for sync. This is done by using manual tune by moving the mouse pointer + to the center of the two bright BPSK carriers in the middle of the signal and left click.

For weak signals and/or when experiencing deep fades, open up the squelch by pulling down the slider. A value of 4.5 is too high for weak signal work. Adjust with signal present to find the best setting without dropping decoded speech.

Split allows independent tuning of the RX frequency. With click tuning, off- frequency signals maybe sync'd without changing the transmit frequency.

Analog changes mode to SSB by routing audio from the receiver's speaker to the  PC headset and the headset mic to the transmitter's mic input.

Transmitting Digital Voice:
Click on TX
and verify RF output level, then adjust your voice level for around 50% deflection on the mic-out display.

TX power out: Run 20-25 watts maximum with a 100w transceiver.
Note: This is an important setting. Attempting to run more power can cause distortion and will significantly degrade the SNR at the receiving station far greater than running lower power. If you must run an amplifier, adjust to about 25% of its maximum power output. Adjusting power for highest SNR and not highest S-meter reports will provide better results.
Generally, SNR can fluctuate rapidly on HF paths.

Analog: Enabling will bypass encoding and decoding for monitoring and transmitting in analog. This provides a quick way of listening on the frequency (with the headphones) and when needed, transmitting in analog (SSB) using the headsets microphone. To transmit, just click on TX and speak in a normal voice while watching the transceiver for proper drive level in SSB mode.
Note: Since the RX and TX audio is being routed through the sound card, a slight delay caused by system latency will occur.

QRGs Used:

FreeDV has only one "official" frequency - 14.236 USB. There are people (VK ONLY) on 7.199 LSB and 7.130 LSB also. The required bandwidth is about 1150 Hz. At the moment your best chance is to arrange a sked.
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