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EasyPal Audio Levels

EasyPal is a program written by Erik VK4AES.  It transfers any data file format on HF, VHF or UHF using a bandwidth of about 2.5 kHz.  It is typically used with SSB mode on HF.  These notes refer only to setting audio levels when using FM mode.

A free download of the program can be obtained from here.  Get the version dated 7 OCT 2014.

See the bottom of this page to get a help file for EasyPal.

If the same PC, radio and interface cable are always used together, the ideal volume settings won't change once they have been set up.

RF Signal Strength

Audio levels should be set while testing with a known-good EasyPal station over a reasonable or strong radio path.  Once set correctly over a good RF path, EasyPal is more likely to decode weaker signals.  Data modes are not usually good at working over weak signal paths, but if EasyPal does decode at least one data segment it can request missed segments to be sent again.

Audio Adjustments

Windows software volume controls adjust the transmit and receive levels.  The data interface between PC and radio may also have adjustments.  If you connect to the radio via a data port, the radio may not have any means of adjusting audio levels.  If you connect via a headphone socket and mike socket, the normal volume control will affect the EasyPal receive audio.  If you have mike gain adjustment on the radio, it will affect EasyPal transmit audio (FM deviation).

These notes assume you use a standard data port, but the principles don't change.  To get reliable results each time that EasyPal is used, notes must be made on the best setting for each volume control.  For the situation of using a standard data port and a data interface cable with adjustable audio attenuation in both directions, this is simple.  Put both Windows volume controls at 50%, then adjust the hardware volumes for the required audio levels.

PC Audio

Usually, you must disable all sound effects and non-flat equalisers, as they add distortion and prevent a flat audio response.  Laptop PCs often have only a mike input socket and a headphone socket.  If a desktop PC has a Line-In socket, the circuitry is usually better quality and should be used instead of the mike socket.  Mike boost amplifiers may be low quality and shouldn't be enabled unless really necessary.  Stereo balance controls should be set to the centre.

The Windows Wave volume is usually best set at maximum, leaving only the Master Volume to adjust the EasyPal transmit audio.  Assuming a laptop PC is used, the two Windows volume controls to be adjusted will be Master Volume for transmit and Microphone Volume for receive.  Note that the PC will have a Microphone Volume control for both Play and Record.  Ignore Play.  You need to adjust the Record Microphone Volume.

Receive Audio Level

This has almost no effect on EasyPal's ability to decode a data file.  EasyPal will decode a file over a large variation of receive audio levels.  Set the Windows Microphone Volume at 50% and adjust the hardware volume control on a known-good received data signal (not open squelch noise, speech or waterfall messages) to be visible in EasyPal's green RX volume bar.  If it is set to the black vertical line at about 95% of the EasyPal's RX volume bar, a large range of receive audio levels will fit into EasyPal's audio spectrum analyser display.

That is the receive audio level sorted out.  The ideal transmit audio level takes longer.

Quick Transmit Audio Level Adjustment

This method is just to get things working the first time you use EasyPal.  It is based on two facts.  Too high a transmit audio level (FM deviation) will be impossible for other stations to decode and EasyPal will decode files over a huge range of receive audio levels.

Either monitor your own FM signal with another radio (it is probably best to remove its aerial to prevent the receiver front end from frying) or get another station to listen to you.  Transmit with a loud voice.  Try to remember how loud it sounded.  With EasyPal transmitting a short file, set the transmit audio to be very much quieter than your voice.  Do this on the data signal, not on any initial waterfall signal.

As EasyPal will decode an almost non-existent audio level on a strong RF signal, this method will guarantee initial success at transferring data files.

Ideal Transmit Audio Level

Once you have some success at using EasyPal, it is best to set the FM deviation to an ideal value.  This is done by another station telling you its received Signal to Noise Ratio (SNR) when you make a series of data transmissions using different transmit audio settings.

Signal to Noise Ratio

The FM mode has a quieting effect on received signals.  As the signal gets stronger, the background noise gets quieter.  A strong signal will have a high SNR value in dB (deciBels).  A weak signal will have a low value.  EasyPal indicates SNR once it has locked to a received data signal.  Notice that this SNR value seems to be averaged and it increases with time.  For that reason, when setting up your deviation level, use the same file all of the time, so comparing SNRs will be valid.

For a silent carrier and a fixed RF path loss, the SNR should remain the same.  With received EasyPal data, the SNR is affected by the deviation level.  It also increases up to a maximum value over time, so use the same transmitted file which takes perhaps 20 or 30 seconds to send.

EasyPal won't lock to the received file unless the initial SNR is about 9 or 10 dB or higher.

The Method

Choose a test file to transmit and arrange a friend to decode your EasyPal data files over a reasonable or strong RF signal path.  EasyPal tells you the time the file will take to transfer.  Set Windows Wave Volume at maximum and Master Volume at 50%.

You will be changing your hardware volume control and need to note its setting and the SNR at the decoding end.  If it is a 270 degree potentiometer, you may be able to guess "degrees clockwise".  If it is a 10 or 18 turn preset potentiometer, you could start at zero transmit audio, then try at 1 turn, 2 turns etc.  I design circuits so that clockwise is louder and anticlockwise is quieter.  Many people do not!

You send the same file each time.  You write down the settings of your volume control.  Your friend tells you the SNR value.  You end up with a table and the maximum SNR value will be seen.  You could then try small changes of transmit audio near that maximum SNR value to improve it.

Ignore any bad segments.  Don't waste time with Bad Segment Requests.  As long as it synchronises, all you are after is the SNR value.  A few seconds after a file is decoded, the EasyPal session log will show the final SNR.  That is where your friend should look to quote the SNR value.

That actual absolute SNR value isn't too important.  You want to achieve the maximum you can get with the radio path used and different transmit audio levels.  Once you have found the best setting, that is it for life if you use the same radio, data interface cable, PC and don't change anything which would affect your transmit deviation level e.g. wide bandwidth / narrow bandwidth.

Sample Table

This table was made in the opposite way to the above suggestion.  The data interface transmit audio volume was kept constant and the Windows Vista Master Volume was changed.  The best deviation level was at 40% volume.

Transmit Volume (%)

Received SNR (dB)

Note

100

13

0 bad segments out of 71

90

16

0 bad segments out of 71

80

19

0 bad segments out of 71

70

22

0 bad segments out of 71

60

24

0 bad segments out of 71

50

25

0 bad segments out of 71

40

27

0 bad segments out of 71

30

26

0 bad segments out of 71

20

24

0 bad segments out of 71

10

17

0 bad segments out of 71

5

11

59 bad segments out of 71

1

--

No sync.

 
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Page updated on 09 January 2017

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