VLF Radio Project

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We love the northern lights, but being in Finland, although the winters are dark, the summers are bright, and we can’t see northern lights for around 3+ months in the summer. Despite the fact we can’t see them, they are actually still there, so we were thinking, how can we still “be in touch” with northern lights if a) the skies are too bright or b) it’s cloudy. The answer is very low frequency radio waves which will enable us to “hear” the northern lights (amongst other ionospheric sounds).

So we bought a VLF (very low frequency) radio receiver kit from NASA and set to work!

It took a long time to arrive from Florida, but once it arrived we set to work building it. Again, like the magnetometer project, it is just a blank PCB (circuit) board with a ton of electronics that you have to solder on. We’re getting pretty good at soldering now thanks to our aurora service projects, so, this VLF receiver was a breeze. It took only 2 evenings and it was done without any issues whatsoever. I don’t have any photos of the soldering/building part, as I just want to get on with it once I get started. But here’s the finished article:

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During testing I was travelling around a bit and going to a local hill trying to listen to what was happening in the ionosphere. I was hooking it up to my iphone to record sessions. They were pretty fruitless though (no northern lights and no particularly interesting sounds). It must be mentioned though, the crackling you can hear on the live stream (which is lightning all over the planet) which is now, pretty normal, when I first heard that sound I was overwhelmed. Imagine being able to hear lightning strikes thousands of km away, even in a different continent!

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Early testing. Hammer was used a grounding rod with my finger on the grounding stud on receiver.

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Recording to iPhone

So I was quite happy with the sound quality so I set up a permanent position for the receiver to stream live here on the website. VLF radio is very susceptible to interference. Even more so than the magnetometer project (!). The VLF radio can hear the electicity cables in your house. Infact just walking next to the house with the radio and heaphones nearly blew my eardrums out. So it was going to have to be far away from the house, much futher than the magnetometer! Which caused a few headaches.

Permanent setup

Version 1

So I had a brainwave of using FM transmitter to send the audio signals from the VLF radio, to a normal radio which would be connected to the laptop in the garden (which is used for the magnetometer and sky camera).

Here’s some pics of it’s install:

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Small copper pipe is a grounding rod. Big copper pipe in background is a 3 metre makeshift antenna. It works quite well, but was picking up a lot of AC interference.

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FM Transmitter

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Audio cable from the headphone socket on HIFI to the laptop mic input.

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Weather proof

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Black cable going into the front of laptop is the audio cable from the HIFI which is set on radio mode receiving the VLF data from the FM transmitter.

Conclusion:
It worked, but the FM transmitter was awful. The maximum range was about 5 metres and the sound quality was pretty poor. So a lot of work and expense for very little in return. I listened to it for a couple days before I got sick of hearing radio fuzz and white noise and decided on a new set up. I was also getting a lot of AC hum from a nearby power lines so the antenna was going to have to be re-located much further away from the house (and power line behind the house).

Version 2

So it was going to have to be a long cable to get out there and connect the VLF radio directly to the laptop. I had about 30 metres of 3.5mm audio cable already, but I was looking at putting the VLF radio about 70 metres away. The 3.5mm audio cable was costing €10 per 10 metres, so I did not want to spend €50 for metres worth. However, purely by chance, I was looking in the bargain basket in the discount store and there was one of these USB Audio Grabber devices reduced from €20 to just €5! I had no idea if it would work, but for 5 euros, well worth a gamble. My logic was, I have tons of cat 5 cable from various projects, with the cat5 to usb converters I already have, I can effectively run any USB device 100 metres away! And so it proved, I connected this USB device about 40 metres away using the cat5 cable, then used the 30 metres of audio cable to connect the VLF receiver. It works flawlessly.

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Small solar panel keeps the battery topped up.

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Copper ground rod to ground the receiver

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VLF receiver, car battery, DC to DC power adaptor for receiver. 1.5w solar panel keeps the battery topped up. (Will need bigger solar panel for winter).

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Pink stuff is Ant repellent due to the box being warm and dry, the ants have taken a real liking to it. It’s just concentrated Chrysanthenum, Ants hate the smell of it.

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This Birch tree is the Antenna. I whacked a pretty big nail in about half way up and connected 25m of solid core copper wire to the nail. Simple, but very effective. It by far beats the cooper pipe we had on previous version.

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This is the view from standing near the house. That Birch tree at the end of the driveway on the left is the antenna and the VLF receiver is in a box next to it. The wooden pole to the left is the earlier versions antenna. A 3 metre copper pipe. It was picking up too much AC noise, but it worked ok.

VLF radio is now up and running, you can listen to it live here

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