Ham radio data modes can are fun and easy to get into. With a data interface sound card, QRP rigs like the Xiegu G1M or the Elecraft KX3 are perfect for data mode communication.
However, commercial data mode sound cards can be expensive which can put some people off. Why? Well they usually include group loop isolation (which is important), they also often include knobs and dials (which are not really so important). Also, they often include a VOX PTT control which is often not needed as long as you have a CAT PTT control of your transceiver.
However, if you wan to rough it a bit, cheap $5 USB sound card combined a $10 USB isolator can perform just as well. Perfect for those wanting to try data modes or for those that just want to keep things low cost.
On this page I'll show you how to make a basic data mode sound card the low cost way, with no compromise on performance.
I purchased the following items, all available from Amazon or ebay:
Without a method to electrically isolate the audio signals between the radio and the PC, it's likely that there will be excessive electrical noise transposed on to your audio signal. This can look like wavy lines on your data screen. The cause of this type of noise is often referred to as a 'ground loop'.
This type of noise can reduce your ability to decode signals, and may impact your transmitted signal. So sooner or later you'll probably want to solve this.
The USB isolator we use here will electrically isolates the sound card from the computer and eliminate those ground loops, improving your ability to decode and send data mode messages.
Connecting the sound card is relatively straightforward. If you get stuck, just stop and think about what is being connected to what.
Note: Ensure your CAT control is set up and working before starting. You will need to key your rig via the CAT lead.
Sound car assembly
1) The USB sound-card plugs directly into the USB isolator, this assembly plugs into your PC or Raspberry Pi
2) The Green jack socket of the sound card connects to the Microphone I/P of your radio. This will provide the audio signal sent from your PC to the radio
3) The Red jack socket of the sound card connects directly to the audio O/P of your radio. This provides the audio from you radio to your PC
4) Connect your regular CAT lead to your radio in the normal way, this will be used to Key your radio and set the frequency.
Fldigi is a good software package for the Pi, Ham Radio Deluxe is good for the PC. The settings for most data mode software differ, but are logical. Usually these settings can be found under the heading Sound card, or Audio.
Configure your favourite data mode software to talk and listen through your USB sound card. These things will usually be configured under the Audio menu, under Settings.
Left channel only!
Configure your software to send audio through the left channel only. This is the tip of the jack plug, this is usually configurable under the software settings.
PTT via CAT
Make sure you can key the radio via CAT, VOX will not work. So you need to get this working correctly for this to work.
Set the sound levels using the relevant sound control sliders for your operating system.
If you are using a Windows PC, I'd recommend using the 'Power mixer' app as this makes adjusting the sound levels easy.
On a raspberry PI just hit the Audio setting button in the top right hand corne er.
Tx output levels: Transmit in to a dummy load, look at your ALC level on your radio. Set the PC audio output level so that the audio level just touches the ALC bar (usually the middle of the ALC scale)
Rx input levels: Look at your data mode software audio bar, using both your PC Mic level and Radio volume knob, set the level appropriately.
I'm very happy with the excellent performance of this simple and low cost sound card. The USB isolator adds the magic by eliminating the ground loops. The Power mixer software makes understanding the sound card arrangement and setting the levels easy.
A great low cost sound card solution for all.
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