News Page 21 - SARCNET

The following section provides installation and configuration of FreeDV. FreeDV is a Windows/Linux/MacOS app, which requires a PC to be connected to your radio. In operation, it fully controls your radio's frequency, mode and PTT. It also requires an additional microphone and speaker connected to your PC as it doesn't use the existing ones connected to your radio.  

Easy Setup

1. Make it safe: Connect your radio to a well-matched antenna or dummy load. Set your radio output power level to minimum.
2. Connect your PC to your Radio, via a USB cable, or using a signal interface unit for older radios
3. Connect an external microphone and speaker to your PC. USB devices are recommended over plug-in analog devices.
4. Open the device manager, on a windows PC, or enter dmesg on a Linux PC, and record the following information (For device manager: You will find this under Audio inputs and outputs and Ports (COM & LPT)):
1. The serial radio control device or port number
2. The audio output/playback device for your radio
3. The audio input/recording device for your radio
4. The audio output/playback device for your external speakers
5. The audio input/recording device for your external microphone
5. Get your station's Maidenhead Grid Square locator here
6. Lookup your radio's serial control (CAT) port's baud rate in the manual and check it in the radio configuration
7. Determine if your radio interface uses CAT or serial port DTR/RTS for PTT signalling
8. Download the latest version of FreeDV for your PC here.
9. Start the FreeDV app and select Tools | Easy Setup
10. Enter the above information into the window shown below and press OK
11. Warning: Pressing the Test button will cause the radio to transmit a full-power carrier signal on the default FreeDV frequency. Make sure that this frequency is compatible with your radio, antenna and licence conditions and is clear to use. Make sure your radio output power level is set to minimum as some radios cannot tolerate full-power carrier signals. We recommend only testing the transmitter after the receiver and transmitter setup is completed below. Do not press Test now.
    

Easy Setup Window

Audio Config

Select Tools | Audio Config - Use this window to check the audio device configuration for both transmit and receive. Note the separate Transmit and Receive tabs. Use the Record and Play buttons to test your connections. Familiarise yourself with the additional settings here. All devices shown will be specific to your PC setup.

Audio Config Window

CAT and PTT Config

Select Tools | CAT and PTT Config - Use this window to check the radio control settings. Press Test PTT to set the radio into transmit mode without sending any signal. This test is safe to use now. Familiarise yourself with the additional settings here.

CAT and PTT Config Window

Options

Select Tools | Options... - Use this window to check reporting and radio control configuration. Only the first two tabs are relevant initially. An important setting is under Rig Control: Use USB/LSB instead of DIGU/DIGL. Modern radios provide different modes for analog and digital operation. This is useful in separately configuring the modulation levels and other radio settings. Check that the FreeDV mode settings match the radio mode settings. Familiarise yourself with the additional settings here.

Options | Reporting Window

Options | Rig Control Window

Filter

Select Tools | Filter... - Use this window to optionally enable graphic equalization on your microphone input and speaker output. Note the use of an AGC for the microphone - It will be mentioned later in Microphone setup.  Familiarise yourself with the additional settings here.

Filter Window

Setup and Operation

The following section provides the setup and normal operation of FreeDV and FreeDV Reporter.  

Receiver setup

1. Open the FreeDV main window
   
2. See image: FreeDV Main Window - Modem Stopped below.
3. Press Stop Modem if it is started
4. Set the Mode to RADEV1
5. Press Start Modem
6. See image: FreeDV Main Window - Modem Started below.
7. Set the Report Frequency (MHz) to the desired band and frequency for testing
8. Check that the radio frequency is automatically set to the required frequency and mode - check analog or digital mode
9. Observe the receiver's waterfall display if it has one
10. Select the FreeDV Waterfall display. Observe that the waterfall display is similar, albeit back-to-front if using LSB.
11. Select the FreeDV Spectrum display and observe the FreeDV Level meter.
12. Adjust the radio receiver volume controls for a mid-range FreeDV Level meter display
    
13. In normal operation, select the FreeDV Frm Decoder display so that you can identify any problems with a transmitting station's audio.  

Transmitter setup

1. Reduce the transmit power to a minimum for testing. Perhaps use a dummy load for safety.
2. Set the FreeDV TX Attenuation control to mid-range
3. Press the PTT button to transmit
4. See image: FreeDV Main Window - Modem Started, Transmitting FreeDV Signal, From Mic Display below
5. Observe your radio changes to transmit mode
6. Safely increase your transmitter power to the desired level while monitoring your antenna SWR and transmitter ALC
7. If too much ALC level is observed, decrease FreeDV TX Attenuation and increase your transmitter power level to compensate
8. Note: FreeDV TX Attenuation sets the signal level into your transmitter, while the radio power level sets the output power
9. Press the PTT button again to receive. Note: It will take some time getting used to the PTT being on the PC not the radio.
10. In normal operation, select FreeDV Frm Mic to monitor your microphone level. Check your radio's SWR, ALC and output power level whenever you transmit.
11. See image: FreeDV Main Window - Modem Started, Receiving FreeDV Signal, From Decoder Display below  

Microphone setup

Since your voice is digitised at the transmitter and then reconstructed at the receiver, it is very important to set your mic level correctly. Note that unlike analog modes the transmitted FreeDV signal, over the air, bears no resemblance to the microphone audio.

1. Press PTT to transmit
   
2. Select FreeDV Frm Mic display
   
3. See image: FreeDV Main Window - Modem Started, Transmitting FreeDV Signal, From Mic Display below
4. Talk normally into the microphone
5. Adjust the FreeDV Mic/Spkr Level control so that your audio waveform peaks are around +/- 0.8
6. Note: FreeDV uses a microphone Automatic Gain Control to help maintain the level set above. It may take time to adjust as you speak.
7. Ignore the Too High indication on the FreeDV Level indicator
   
8. Stop talking and check the residual audio waveform: There should absolutely be no signal displayed! FreeDV does not like ANY background noise like fans, hum, music or monitored audio. It confuses the voice encoder and is greatly accentuated in the received audio, causing harsh sounds and voice distortion.
9. Press PTT again to receive
10. To test the microphone setup:
1. Press PTT to transmit.
2. Press Record
3. Speak normally for a period.
4. Press Record
5. Press PTT to receive.
6. Select Tools |  Start Play File - From Radio ...
7. Select the latest FreeDV_FromRadio .wav file.
8. Your recording will be played back.
11. In normal operation, select the FreeDV Frm Mic display so that you can identify any problems with your own audio.
12. Notes:
    
1. The FreeDV microphone level is only adjusted when the PTT is activated.
2. Setting the microphone level does not change the transmitter input signal level or its output power level.
3. You do not need to readjust the FreeDV TX Attenuation or radio power level after adjusting the FreeDV Mic Level.
4. FreeDV takes full control of the PC audio devices. Do not try to adjust them using the operating system windows.  

Hard-Wired PTT Setup

FreeDV Press-To-Talk (PTT) operation is normally via the onscreen PTT button or the keyboard spacebar. Both of these methods are problematic: If the FreeDV window looses focus, amidst all the other windows on the desktop, finding it can be time-consuming. While the spacebar is an alternative PTT method, holding it down for more than a second causes the PTT to go on and off at the keyboard-repetition rate.

The ideal solution would be a combination momentary-operation and locking, hard-wired PTT switch: This can be achieved using a USB to TTL* Serial Adapter module as shown below. The module must support a CTS input. Connect the CTS input (blue wire) and GND (green wire) to your PTT press-button or toggle switch. Open the FreeDV | Tools | CAT and PTT Config window and in the PTT In frame: Select Enable PTT Input, for the Serial Device select the USB to TTL Serial Converter module's COM port and select CTS = +V. The switch will now control the FreeDV PTT! If you have problems with RF getting into the CTS line, add a 0.01uF chip capacitor to the rear of the PCB.

(*) Note: If you have an RS-232 adapter instead of a TTL adapter, you need to connect the PTT switch between the RTS output (pin 7) and the CTS input (pin 8).

Important: You might be tempted to wire the CTS/GND lines in parallel with your existing desk microphone PTT switch, such that the PTT signal will go to FreeDV and the radio at the same time. Dont! The USB to TTL Serial Converter module must only control the PTT signal to FreeDV, while FreeDV must control the PTT to the radio via the CAT cable. This is because FreeDV holds the PTT active at the end of each over for a short period in order to transmit an End-Of-Over Information Frame, over the air. The parallel connection would cause this frame to be cut off. The result is that your callsign will not appear in the RX Call column of FreeDV Reporter, and worse, everyone's receiving decoder will produce a burst of gobbledegook at the end of your over.

Options:

1. You could wire up a "PTT Selection Switch" to direct the PTT signal to either the FreeDV USB to TTL Serial Converter or to the radio.
   
2. If your radio has a 12V PTT line (e.g. a relay coil pulled up to 12V) you might need to add an opto-isolator to the USB to TTL Serial Converter to protect it.
3. You can wire the PTT line in parallel with your existing desk microphone PTT switch if you are using Thetis software with an SDR radio. Thetis supports saving and restoring individual databases containing all the radio settings for each mode you use. So, for the FreeDV mode database: Turn off Setup>General>H/W Select>Hardware Options>PTT. For the Analog SSB mode database: Turn it on.      
   

USB To TTL Serial Adapter module

CAT and PTT Config for Hardwired PTT

FreeDV Operation

Start the FreeDV app - The FreeDV main window is displayed

1. FreeDV starts with the modem stopped
   
2. The Start button is displayed
3. The following settings are only available when the modem is stopped:

1. Audio Config
2. CATT and PTT Config
3. Mode

FreeDV Main Window - Modem Stopped

Press the Start Modem button

1. The FreeDV modem is started, in receive mode
2. The following controls and displays are only available when the modem is started:
1. Stop Modem button
2. Switch to Analog
3. Start Voice Keyer
4. PTT
5. Mic/Spkr Level
6. SNR and Level meter
3. When no signal is being received the waterfall will display a random, salt-and-pepper pattern
4. The SNR meter will not be active
5. The RX level meter should indicate a low-to-mid range audio signal from the radio
6. Check the waterfall for stations using the frequency:
1. Look for vertical lines in the waterfall which often represent carriers, CW or RTTY signals using the frequency.
7. Press Swich to Analog
1. Listen for SSB signals using the frequency.
8. Press Switch to Digital
   

You should always check the waterfall and analog mode to see if the frequency is in use before transmitting.

FreeDV Main Window - Modem Started, Not Receiving FreeDV Signal

Start receiving a FreeDV signal

1. You can hear the decoded FreeDV signal from the speaker
2. Use the Mic/Spkr Level control to adjust the volume
3. The FreeDV speaker level is only adjusted when the PTT is deactivated
4. The SNR meter shows the current received SNR. The SNR changes quickly so turn Slow off to monitor it carefully.
5. The RX level meter should indicate mid-range audio signal from the radio   
6. The Sync indicator shows a FreeDV signal is being decoded
7. The waterfall shows a 1.5 kHz wide signal centred on 1.5 kHz. The signal comprises 30 OFDM carriers spaced at 50 Hz.
8. Either side of the main signal are some vestigial filter artifacts. These are not part of the signal and can be removed with RX filtering - See later.

FreeDV Main Window - Modem Started, Receiving FreeDV Signal, Waterfall Display

Select Frm Decoder while receiving a FreeDV signal

1. The station's audio waveform is displayed. It is a bit low here: Only +/- 0.5.
   
2. There is some background noise between words
3. The station's SNR is 12dB: 2 full S-points above the local band noise level. Lower power levels could be used.
   

FreeDV Main Window - Modem Started, Receiving FreeDV Signal, From Decoder Display

Press the PTT button and select Frm Mic

1. Use the Mic/Spkr Level control to adjust the microphone level only in transmit mode
2. The microphone audio peaks are measuring +0.4 and -0.8. Human voice is often asymmetric. However, the peaks should not exceed +/- 0.8
3. The microphone level is zero (no green line) between words, as there is no background noise

FreeDV Main Window - Modem Started, Transmitting FreeDV Signal, From Mic Display

FreeDV Reporter Setup

Select Tools | FreeDV Reporter - The FreeDV Reporter window is displayed

This FreeDV Reporter window displays the following columns:

1. Callsign - The call signs of all operators reporting to FreeDV Reporter.
2. Locator - The Maidenhead locator of each station
3. km - The distance to each station from your location
4. Hdg - The heading to each station from your location
5. Version - The version of FreeDV used by each station
6. MHz - The operating frequency in Megahertz of each station
7. Mode - The FreeDV Mode used by each station
8. Status - The status of each station: RX, RX Only or TX.
9. Msg - The message being sent by each station
10. Last TX - The last time the station transmitted
    
11. RX Call - The last call sign received by each station  
12. Mode - The mode used by the last call sign received by each station
13. SNR - The Signal To Noise Ratio received by each station
14. Last Update - The last time the station info was updated

The rows are displayed in the following colours:

1. Red - The station is transmitting FreeDV
2. Teal - The station is receiving FreeDV
   
3. White - The station is not receiving FreeDV
4. Purple - The station has recently changed the message
5. Grey - The station has been selected

FreeDV Reporter Window - Unfiltered and Sorted by Call Sign

FreeDV Reporter Operation

The FreeDV display can get very cluttered with many stations on different bands, all around the world, all using FreeDV. The position of stations in the list changes frequently. To view only the stations on your frequency and to stop them moving around the list, do this:

1. Select km ^
2. Select Band: All
3. Select Track
4. Select Freq

Your station will always be displayed at the top of the list and only the stations on your frequency will be included in the list, sorted by their distance from you. Please send a message identifying yourself, such as your name and location, to everyone using FreeDV. Enter your message and press Send. Save your frequently-used messages by right clicking on the send button.

FreeDV Reporter Window - Filtered and Sorted

You can further optimize the layout by using the Show menu (new in version 2.2.1) to select only the columns you need and then sorting the columns by dragging them into the best positions. In order to get the most important Callsign and SNR columns together we sorted the columns, left to right, into the following order:

1. Callsign
2. SNR
3. RX Call
4. km^
5. Status
6. MHz
7. Version

Hints and Tips

1. Don't blow up your radio - Check it's output power level, ALC and SWR each time you PTT.
2. Always check that the frequency is not in use before transmitting. Since you can't hear CW, RTTY and analog SSB signals through FreeDV in Digital Mode you have to press "Switch to Analog" to listen and also check the Spectrum/Waterfall displays before transmitting.
   
3. FreeDV audio can be categorised as follows:
   
1. Practically Perfect.
2. Strangled: Screeching and high-pitched.
3. Explosive: A cough or a sneeze is greatly exaggerated.
4. Garbled: Readable, but interspersed with unreadable voice-like sounds.
5. Gibberish: Completely unreadable voice-like sounds.
6. Muted: Constant, occasional or frequent audio drop-outs.
4. When FreeDV audio is less than Practically Perfect the cause can be:
1. Incorrect microphone audio level settings: Too high or too low.
2. Windows microphone "enhancements" are turned on: Causes your voice to sound high-pitched and strangled.
3. Any form of background noise will be significantly exaggerated and cause garbling of you own voice.
4. Turning on "Monitor Transmitted Audio" (right-click on PTT menu) will create significant echo and background noise.
   
5. A cough or a sneeze: FreeDV was optimised using machine learning for human voice, not influenza.
   
6. RF feedback into the microphone or CAT control USB cables: Pass the cable 6 times through an FT-140/43 toroid.
7. Frequency offset: FreeDV can tolerate +/- 50 Hz transmitter frequency offset. There will be no decoded voice at +/- 100 Hz offset. This can be problematic for older (tube) radios with analog VFOs.
8. Having Ionospheric, frequency selective, multipath fading: Vertical, horizontal or oblique striations or holes in the waterfall display.
9. Static Crashes caused, by lightening, creating short periods of negative SNR.
10. Low signal level, poor propagation or slow fading causing signal to fall well below the band noise level. -2dB SNR will work. -3 to -5 dB SNR may work under calm conditions. Less than -5 dB SNR will be muted.
11. Normal: FreeDV will always perform better than analog SSB under the same conditions, so don't panic if the audio drops out.
5. Press To Talk:
1. Learn to use the on-screen PTT, not the radio PTT. Keep the FreeDV window in focus. Get ready: Pre-emp PTT changeover!
2. While the keyboard spacebar can be used for PTT, holding it down too long will causes oscillation of TX and RX mode.
3. A hard-wired PTT switch can be constructed using a USB-TTL Serial Converter. See above.
6. Use FreeDV Reporter effectively:
1. Set up filters and sorting.
2. Send your name and location.
3. Save frequently used messages (Right-click on Send).
4. Indicate your operator status in your message: Include "Away" if you are not able to respond.
5. Welcome new stations appearing for the first time on FreeDV Repoerter and help them to get set up.
6. Don't ask "How are you receiving me?" all the time - Check FreeDV Reporter first.
7. Monitor your SNR at all receiving stations. If you are less than -2 dB, increase power or wait and repeat what you just said.
7. The maximum digital power level in Australia for the various licence types is 120 W Average (Advanced),  30 W Average (Standard) and 10 W PEP (Foundation). Note that your Peak Envelope Power will be significantly greater than Average power. See below.
8. Use Frm Radio display when setting up to monitor the received audio level.  
   
9. Use Frm Mic display while transmitting to monitor your mic audio level.
10. Use Frm Decoder display while receiving to monitor the other station's audio. Report issues of incorrect level or background noise.
11. Adjust the Frm Radio audio level peaks to +/- 0.8 using a combination of the radio's RF and AF gain controls just as you would when receiving a SSB signal: Reducing the RF gain may improve SNR.
12. Adjust the Frm Mic audio level peaks to +/- 0.8 using the FreeDV Mic Level control. Ignore Clipping indications.
13. Initially turn off all receiver processing like noise reduction and noise blanking. Select Fast AGC. Experiment to see if they improve SNR.
14. Set both your TX and RX bandpass filters on your radio, if you have them. The bandpass should be 750 Hz to 2250 Hz. This will  (slightly) improve SNR on receive, but greatly improve your Peak to Average Power Ratio on transmit.
    
15. Don't have long QSOs on the FreeDV calling frequency. QSY.
16. Don't test on net frequencies, which are monitored by stations all day: QSY or use a dummy load.
17. Where to QSY? See your band plan for where Digital Voice mode is acceptable. E.G. In Australia on 40m: 7060-7074, 7080-7300.
18. Request a station to QSY to your frequency:
1. Turn off Band or Frequency Tracking
2. Select a station on a different frequency using the left mouse button - Deselect a station with the right mouse button - The station colour will change to grey.
3. Press Request QSY - The station will receive a prompt to optionally QSY to your frequency.
19. Use only the radio output power level needed for a positive SNR at receiving stations. Adjust power with FreeDV TX attenuation control.
20. You can leave FreeDV running all day on speaker with no background noise and be alerted to anyone calling on the frequency.
21. Long USB and Analog audio cables are easy entry points for RF. RF in the shack is rarely a good thing. This can cause noise on USB microphones and USB CAT control issues. This is called RF Feedback.
    
1. Try looping USB and Analog Mic cables a few times through an FT-140/43 toroid.
2. For USB ports a USB hub, with internal magnetics, may help reduce RF input.
3. Unbalanced antennas should have properly designed current baluns which act as common mode chokes.  

Power Limits:

Foundation: Any Mode: 10 watts pX.

Standard: Mode J3E: 100 watts pX. Other modes: 30 watts pY.

Advanced: Mode J3E: 400 watts pX. Other modes: 120 watts pY.

In this instrument, the emission mode of a transmission made by a radiocommunications transmitter is the designation of the emission worked out in accordance with Appendix 1 (REV.WRC-19) of the Radio Regulations... which states:

Classification of emissions and necessary bandwidths, Sub-Section IIA – Basic characteristics

1.2.4) Single-sideband, suppressed carrier: (J)

2.3) A single channel containing quantized or digital information with the use of a  modulating sub-carrier: (2)

2.4) A single channel containing analogue information: (3)

3.6) Telephony (including sound broadcasting): (E)

pX (Peak Envelope Power - PEP): The average power supplied to an antenna transmission line during one radio frequency cycle at the crest of the modulation envelope.

pY (Mean Power): The average power delivered over a time period sufficiently long compared to the lowest modulation frequency.

With TX Filtering (700 Hz - 2300 Hz): 4.7 dB

Without TX Filtering: 3.3 dB

Using FreeDV with SDRs

For FreeDV we use our Apache Labs ANAN 200D transceiver with Thetis SDR Software. This is an excellent SDR combination with so many great features. For example: We use Thesis "Pure Signal" adaptive pre-distortion processing with our Elecraft KPA500 amplifier for very linear digital operation. Thetis also has the advantage of being able to save the entire transceiver configuration, including modes, bandwidths, audio input/output devices, levels, etc in separate databases. However, for anyone using Thetis software with an SDR (e.g. ANAN or Hermes Lite 2) there are a couple of settings that really make a difference to the receive audio quality. Without these settings you will get quite a bit of garbled audio from FreeDV. The basic idea is to ensure linear, wide and non-aggressive filtering. To set up Thetis for FreeDV go to the Setup | DSP | Options tab and enter the following settings in the SSB/AM section for both RX and TX:

1. Buffer Size = 64 (i.e. minimum)
2. Filter Size = 1024 (i.e. minimum)
3. Filter Type = Linear Phase (not Low Latency)
4. Filter Windows = BH-4 (not BH7)

FreeDV TX Band-Pass Filters

The vestigial side-lobes either side of the main lobe of the FreeDV waveform contain no useful information, but they are only 10 dB down. So we decided to filter them out using the TX bandpass filter capabilities on our transmitter. As can bee seen below, bandpass filtering the waveform from 700-2300 Hz, at the maximum permitted average power level of 120 W, increased the Peak-To-Average power ratio by 1.4 dB or 100 Watts Peak Envelope Power. So that was worthwhile. The measurements were taken using an uncalibrated Telepost LP-100A Digital Vector RF Wattmeter.

FreeDV Spectrum and Waterfall - No TX Bandpass Filtering

FreeDV Peak, Average and Peak-To-Average Power Ratio - No TX Bandpass Filtering

FreeDV Spectrum and Waterfall - 700-2300Hz TX Bandpass Filtering

FreeDV Peak, Average and Peak-To-Average Power Ratio - 700-2300Hz TX Bandpass Filtering

Conclusion

FreeDV is a game-changer, but it is not for everyone:

CONS: Additional PC, microphone and speaker. On screen PTT.

PROS: Better than analog SSB in all respects.

Call into SARCNET on 7083 kHz FreeDV any day from 9am to 6pm Melbourne, Australia local time!