Remote Digital using SmartSDR 1.4 LAN over VPN

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  • Updated 3 years ago
This is a continuation after you have successfully setup a VPN to your home network to connect to your radio remotely.  Documentation on how to do that can be found here.   This setup will let you run digital apps locally over the VPN link to your remote Flex 6000 radio.


Currently DAX over VPN isn’t feasible.  For some fast internet connections it may be OK, but when I’m stuck in a hotel using my metered iPhone or the crappy hotel WiFi,  I doubt I could sustain a solid 2Mbps for any length of time.  A single DAX channel is uncompressed and streams at ~1570kbps.  The Opus codec currently uses 77kbps each direction.   Until DAX is optimized to work over WAN, I wanted to utilize the compressed opus stream and see if it was sufficient to do digital modes.   My results show that not only is it possible, but it works quite well.

To do this, we need a clever way of manipulating the audio in and out from SmartSDR and feed it into the digital app of choice and also get audio back out to SmartSDR.  If possible, we’d also like a copy of the audio sent to the laptop’s speakers for listening.   I have found a way to do this.

The product I use is called VoiceMeeter Banana.   I worked with Ed W2RF a few months ago testing VoiceMeeter's latency and for voice it is a bit too high without using ASIO drivers.   The added latency is about 40ms using WDM if you drop the buffers down to around 256.  For latency tolerant digital modes, this hasn’t caused any issue.   This method will not work with latency sensitive modes such as ALE400 or WinLink WinMor.

Download Link for VoiceMeeter Banana:

VoiceMeeter installs two sound cards and two microphones into your system.

Under Playback:
  VoiceMeeter Input
  VoiceMeeter Aux Input

Under Recording:
  VoiceMeeter Output
  VoiceMeeter Aux Output

The “VoiceMeeter Input” playback device routes to the virtual input labeled “Voicemeeter VAIO”.  The “VoiceMeeter Aux Input” playback device routes to the virtual input labeled “Voicemeeter AUX”.  “VoiceMeeter Output” microphone is B1 and “VoiceMeeter Aux Output” microphone is B2 inside the application.

In the top right corner, you will see A1, A2, and A3.  This is where you define routing the audio output to real sound devices, such as our laptop speakers.   In this setup,  I picked “Speakers”.  The left three Hardware inputs are where we get audio in from physical devices.  For Hardware Input 1, I picked my laptop’s internal microphone just in case I needed it.  Each input and output has it’s own gain slider.   I will use this setup to create two parallel audio paths.  FLDigi will be used as an example.

For this configuration, you must set “VoiceMeeter Input” as your default playback device and “VoiceMeeter Output” as your default recording device.

I route audio from “VoiceMeeter VAIO” to both the speakers (A1) and out of the VoiceMeeter AUX Output (B2).  We will now hear the audio from SmartSDR and have a way to route another copy of the audio into FLdigi.

I route audio from FLDigi back into Voicemeeter by setting the Playback sound card in FLdigi to “VoiceMeeter Aux Input”.  In VoiceMeeter we now enable that audio to flow out “VoiceMeeter Output” (B1) which is the system’s default microphone.  This feeds into SmartSDR and out to the radio. 

Make sure you have PC selected as your microphone in SmartSDR.  Make sure you are using DIGU to disable any processing of the audio signal.   Setup SmartCAT to PTT just as you would normally.   I use a PTT trigger.

Set SmartSDR’s main volume to 100%, and vary the Slice’s AGC and volume to satisfy FLdigi’s input level requirements.   Adjust either FLdigi’s gain output or manipulate the Fader Gain slider in VoiceMeeter virtual input “VoiceMeeter AUX” to make sure you do not overdrive SmartSDR’s input.

I was able to use every mode in FLdigi and JT65 without issue for hours.   If i kept my FPS and WF rate low, my total bandwidth usage was about 200kbps in and 120kbps out.

I recorded a YouTube video to better explain it.

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K6OZY, Elmer

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Posted 3 years ago

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Very nice! Thanks for sharing!