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 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

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And then I met Lara Croft! But this story doesn’t have a happy ending…

I have a very modest PC which runs 24/7 in support of my website. The on board 800MHz graphics was fine for most things, but not particularly good for gaming.

For years I’ve been following a development called Space Engine. The program (for PC) has been in beta mode for at least five years. It’s a graphics hungry universe simulator which recreates the known (and unknown) universe on a scale of 1:1. It’s totally awesome. It ran reasonably well on my machine when set with the lowest graphics settings, and I loved it.

About a month ago, Space Engine launched its first paid (but still under development) version on Steam. It costs just under £20. To cut a shortish story even shorter, it didn’t run at all with my graphics card. This was kind of expected, although disappointing. I needed to upgrade the graphics card, so I bought the (recommended) Nvidea Geforce GTX 1060 for about £180.

Yay! It ran perfectly for all of… 10 minutes. As the graphics became more complex (ie when cruising near a super-massive black hole), the PC fans got faster and faster, then it shut down. That’s the thermal protection kicking in… but that’s not surprising that close to a black hole. To get an idea, check out this video:

In fact I found that it crashed the computer far too often, and I soon realised that I should make sure the graphics firmware was up to date. Sure enough, the supplied driver version was about six months old. The update and some lowering of the graphics card clock speeds reduced the number of crashes.

Now, what’s this all got to do with Lara Croft? Well, I’ll tell you. Nvidea were bundling Shadow of the Tomb Raider with the graphics card, so it occurred to me that they would only do this if they were confident that the card would run ok with it without getting too hot. As I wouldn’t normally play games like this (mainly due to my rubbish system!) I gleefully downloaded the massive 28GB game overnight, and gave it a try.

It seemed to run fine, (except Lara seems to look a bit like Princess Fiona from Skrek, but that’s not going to be the fault of my system).

I digress… So I ran the game for about 10 minutes, playing through the intro and in-game videos with ease, and then on to some actual game play. I then hear the fans in my PC winding up the revs faster and faster as the intensive jungle scenes are shown. “Ah!” me thinks, “This game is supposed to run fine with this graphics card, else they wouldn’t have offered it for freeeee!!”

It was the last thought I had before… BANG! Followed by electrical crackling noises, and my screens went dead. The strong and sweet smell of burnt insulation wafted around the room and all was quiet, except for my daughter calling from the room next door “Dad, what just happened?”

I fear that I should have heeded the warning signs when I was orbiting Saturn a couple of days ago…

So, the long and the short of it is that I hadn’t checked the power budget and it blew at least one resistor in the power supply.

The GTX 1060 requires 400W. My PC had a 500W PSU. It also had a motherboard with a 4 GHz CPU, three disc drives and multiple fans to supply. The picture above is the result.

So, an 850W PSU is on the way, costing another £55.

My appointment with Lara is on hold… so meanwhile here is a video of Space Engine on Youtube for you to enjoy.

My feeling is that the site is now running “optimally”, excepting for some caching on the left side bar. Opening the site in an “incognito” browser window on a mobile or desktop will stop any caching at all and may be the best option.

Since it went live last week I’ve added some new features. On both the European Sporadic-E and HF Propagation (W Hemi Zoom) maps, via a link below the maps you can find timelapse videos. These are located on a 3rd party site ( Using controls below the videos you can adjust the period of view and frame rate.

Server: Running
Live maps updating: Normal
Map upload rate to server (FTP): Once per 1 minutes
Map page refresh rate: Once per minute

Hair loss: 40%

Following the site move to my new web host (Krystal) I’ve had several issues. By far the worst was image caching which prevented pages from live-updating.

I knew the key was in the .htaccess file, but it took a while to find the correct coding to defeat caching that worked on my server. That’s done now and the map pages are updating normally on desktops. There’s still a caching issue on mobile browsers where the left side info bar images are very out of date (by hours). I’m not sure if I can solve that particular problem as it might be a phone-based cache. Switching off “Lite” mode (on Androids) might help.

Server: If you can read this it’s up!
Live maps updating: Normal
Map upload rate to server (FTP): Once per 2 minutes
Map page refresh rate: Once per minute

Hair loss: 90%