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)

Software required:
SDR Console v3 x2 instances (download here)
Zello v2.6 (free account required)
VB-Audio Cable (first one free)

Zello (PC version)

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).

Zello (Android version)

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 wit hthe 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…


This article was first published on Sciencemag.org on 9th October 2020.

Starlink already threatens optical astronomy. Now, radio astronomers are worried

The 197 radio astronomy dishes of the Square Kilometre Array (SKA) in South Africa will sit within a radio-quiet zone the size of Pennsylvania where even a cellphone is forbidden, to preserve the array’s views of the heavens. Yet that precaution won’t save the telescope, due to be completed in the late 2020s, from what may soon be overhead: tens of thousands of communications satellites beaming down radio signals straight from the heavens. “The sky will be full of these things,” says SKA Director General Phil Diamond.

The rocket company SpaceX has already launched hundreds of Starlink satellites, the first “megaconstellation” intended to provide internet service to remote areas. The satellites have aroused the ire of optical astronomers because of the bright streaks they leave across telescopes’ fields of view. Now, radio astronomers are worried, too. This week, SKA released an analysis of the impact that Starlink and other constellations would have on the array. It finds they would interfere with one of the radio channels SKA plans to use, hampering searches for organic molecules in space as well as water molecules used as a key marker in cosmology.

SpaceX is promising to address the concern. But radio astronomers are also seeking regulations. The United Nations Office for Outer Space Affairs (UNOOSA), which discussed the SKA analysis at a workshop this week, is considering ways to keep satellites from polluting the night sky with light and radio signals, not just for astronomy, but also for wildlife and the public. Astronomers also hope the International Telecommunication Union (ITU), a U.N. organization, will step in. “The radio spectrum is a resource that is being consumed by private companies that typically have no regard for science,” says radio astronomer Michael Garrett, director of the Jodrell Bank Centre for Astrophysics in the United Kingdom. “It’s only government intervention that can stop this state of affairs in my view.”

So far, SpaceX has launched more than 700 Starlinks out of an initial goal of 1440, and it has won approval for 12,000. Other operators, such as OneWeb and Amazon’s Project Kuiper, have similar ambitions. Studies suggest wide-field optical surveys will be worst affected, with satellite tracks marring most images. The team building the Vera C. Rubin Observatory, a survey telescope in Chile due to see first light next year, has been working with SpaceX to reduce the impact. The company has changed the orientation of satellites as they move up to their final orbit, painted them a less reflective color, and fitted “visors” to reduce reflections. Since August, all launched Starlink satellites have visors, SpaceX’s Patricia Cooper, vice president for satellite government affairs, told the UNOOSA workshop this week. “We’re trying to look for a path where we can coexist,” she said.

The analysis from SKA, which when complete will be the world’s largest radio observatory, highlights the new concern. The band that Starlink uses to beam down internet signals takes up a sizable chunk of frequencies from 10.7 to 12.7 gigahertz, within a range known as band 5b that is one of seven bands SKA’s South African dishes will target. The SKA analysis calculated the impact of 6400 satellites, taking into account both direct signals and leakage called “side lobes.”

The team calculated that satellite transmissions will lead to a 70% loss in sensitivity in the downlink band. If the number of satellites in megaconstellations reaches 100,000, as predicted by many, the entire band 5b would be unusable. SKA would lose its sensitivity to molecules such as the simplest amino acid, glycine, a component of proteins. “If it was detected in a planetary system that was forming, that would be a very interesting piece of information,” Diamond says. “This is a new area that SKA is opening up.” The band could also contain the fingerprints of water molecules in distant galaxies, a tracer that cosmologists use to study how dark energy is accelerating the expansion of the universe.

Since 1959, ITU has protected a number of narrow frequency bands for astronomy. But in recent decades, digital receivers have allowed telescopes to “operate over the whole spectrum,” Diamond says. “We’ve learned to coexist with transmitters,” typically by excluding them from a radio quiet zone or siting telescopes in remote areas. But they have no control over transmitters flying overhead.

Radio astronomers want the satellite operators to turn off their transmitters, move to other bands, or point them away, when they are flying over a radio observatory. Tony Beasley, director of the U.S. National Radio Astronomy Observatory, says they have been discussing these options with SpaceX. “In the next year or two, we will be doing tests where we’re going to be trying to coordinate in real time, technically, with them.” Beasley says this is a reflection of SpaceX’s corporate culture: “They want to do cool stuff; they don’t want to do any harm.”

Other astronomers don’t want to count on corporate goodwill. At the UNOOSA workshop, they pushed for two recommendations: that all future satellites in low-Earth orbit be designed to avoid beaming at radio telescopes and radio quiet zones, and that they control the leakage from their side lobes. Those recommendations, along with others discussed this week for protecting optical observatories, will be debated at a series of U.N. subcommittees next year before going to UNOOSA and, ultimately, the U.N. General Assembly for approval.

Beasley is philosophical about the situation. “SpaceX is legally transmitting inside one of their bands and there are going to be impacts for anyone trying to do radio astronomy,” he says. “These spectrum allocations represent the goals and intent of society. We make [them] to enable commerce and to enable defense and all kinds of activities. We have to come to a solution that satisfies all these to some extent.”

*Correction, 12 October, 7:30 a.m.: An earlier version of this story incorrectly stated that glycine is a component of DNA.

By Daniel Clery Oct. 9, 2020 , 2:25 PM

Posted in: 

doi:10.1126/science.abf1928