This article describes how to listen to multiple channels of HF and VHF utility radio services on a mobile phone, sourced from my SDR receivers at home. If you don’t have the time to always be in your radio shack to hear the action, this article is for you.
I will not explain how to install SDRs, antennas and computer programs. I’ll just tell you how to link them together to obtain the required result. It is assumed that the reader is already familiar with how SDRs and computers work.
I’m running an SDR Play RSP1a with 8 MHz bandwidth tuned to the MF and lower HF bands, plus an RTL Dongle tuned to 2 MHz of the lower part of the VHF Marine Band. The VHF SDR is fed from a discone antenna which is located on my chimney. The RSP1a is fed from a YouLoop located at ground level, but sometimes I take a split from the Discone feed depending upon the interference level. Channels regularly monitored include 2182, 3924, 5680 kHz, and a variety of public VHF marine channels.
Hardware prerequisites (for my setup):
2x SDR receivers (SDR Play RSP1a, RTL Dongle R280T)
Desktop computer running Windows 10 64bit (i7 9700 3GHz processor, 32GB RAM)
1 TB SSD Hard drive for OS and SDR applications
Samsung Galaxy S8 phone (with a large data plan)
Discone antenna (no preamp)
YouLoop MF/HF/VHF antenna (no preamp)
SDR Console v3 x2 instances (download here)
Zello v2.6 (free account required)
VB-Audio Cable (first one free)
What to do?
Zello is the hub of this exercise. It’s a “walkie-talkie” application designed to be used for audio chat across the internet on public or private channels, using “push-to-talk” or VOX (voice operated switch) methods. There are mobile versions for iPhone and Android, plus a PC version. There are also personal and business versions. The Zello website steers you towards the paid version without mentioning the free personal one, so follow my link and sign up for free. You can send audio from your home computer to your mobile phone (and vice-versa if needed).
Install the mobile app to your phone and the PC version to your computer. Open one or other and create an account. On the other device create a different account, and log in to both. Add each account as a contact on each device.
Zello allows users to set up public channels, but we’re not going to create a channel for this purpose. Public channels are unencrypted, and anyone can listen in (unless you wish to make your PC’s audio public, of course!) The connection between your PC and mobile will be via a direct “user to user” link, which remains encrypted and private. If you have more friends who you want to have listen in, they can also be added as contacts.
Next, install and configure the virtual audio cable on your PC, if you don’t already have one. The SDR(s) will need squelched audio to be fed to the virtual cable input, with Zello listening to the same virtual cable output (in Tools, Options, Audio). In my example I’m using VB-Audio Cable B.
Put Zello into “VOX” mode on the PC (in Tools, Options, Vox). Test it with the default settings and adjust the thresholds and trigger times later if needed.
Start your SDR software (in my case SDR Console v3) and set up the multiple tuners listening to your channels of interest. Ensure that the audio is squelched so that noises bursts are minimised, and select the virtual audio device for the output. If you have further SDRs for different bands, open “new instance” for each one with a different (saved) configuration from SDR Console’s menu and repeat the exercise, outputting the audio to the same virtual cable. Check that the squelch is enabled with the threshold as low as possible before noise causes it to break.
Now, when the SDR’s squelch opens, audio is sent through your Zello account as the VOX keys the link via the Zello servers and onwards to your mobile. The Zello system has the advantage of storing your incoming audio messages, so if you miss something you can scroll back through the history and replay it. You can also set the history to be kept for varying lengths of time.
To make things ultimately flexible, connect your phone via Bluetooth to your car audio system for when driving around, or to an earpiece for private listening.
And finally, a gratuitous picture of one of my curious cats…