VLF radio receiver build

[HN50]

I need to get round to building a case for my ST102, but with a lot of diy recently I can't quite face any more sawing.  So I had been thinking about a little project for my holiday.  

I had stumbled onto some websites showing circuit diagrams for VLF radios to listen for lightning - the astronomy bit is that they can also apparently pick up the effects auroras :).  Electronics has always been a bit of a mystery to me, I understand what the individual bits do but arranging them to do something useful other than lighting up a LED is beyond me.  In the end I opted for the peanut butter radio in the following link;

http://www.techlib.com/electronics/vlfwhistle.htm

I then ordered a breadboard and enough components to make four (insurance from accidents, dodgy soldering, rabbit attack etc).

After a day of poring over the diagram and adding components to the breadboard the creation in the photo came into being.  The aerial is the looped wire with the knot in the end, while the wire seemingly connected to nothing is the earth.

To my considerable surprise when I turned it on I could hear it making a humming noise. I took it out into the garden and I think that all the A/C power cables nearby are interfering, but I could start to hear the frying pan sound of lightning.  

Following the schematic was fun, and although the circuitry is all over the place it wasn't as difficult to do as I thought it would be - a bit like a crossword or sudoku.  So if you have ever wondered about trying it,  give it a go.

The prototype is not very rugged as the earth and aerial keep falling out, so the next part is to replicate it on veroboard and fully solder it.

And that I think is where everything will get rather more tricky!

Dave

 

 

 

Edited August 17, 2016 by HN50

[HN50]

Have been soldering this afternoon, still more to do but might have to stop for evening (too much frowning!).  But anyway, two pictures of progress so far.

[Alien 13]

That`s good progress looking forward to seeing how it performs, might have a go myself at one of the projects in the link.

Alan

[HN50]

Hi Alan,

Thanks for the reply, if I get a double pin connector I will see if my iPhone can record it.  There are a few national trust sites nearby that are well away from power lines so hopefully domestic interference will be little to non-existent.

Another website I found us this one;

http://www.stormwise.com/project1.htm

I think that is simpler but it looks like it is intended for speakers rather than headphones.  

Dave

[HN50]

I carried on soldering and found that it did not work.

I started trying to debug the circuit and found that the way I had laid it out was rather difficult to follow - rather than using the line of the copper strip to get the current to earth I had used wires to jump across them, so there were a heck of a lot of additional solder joints that could be avoided with better circuit layout.

So I started again (and decided I really should buy a multimeter) with the strips going along the length of my board and not across it.  After a day's soldering I turned on Attempt 2...

It still didn't work.

There was a burst of noise when turned on, then nothing.  At this point I put it aside in annoyance and did something else for a week and a half.

However an unfinished project does irk me, so earlier this afternoon I got it out and used the multimeter to try and find if there were any accidental short circuits messing things up.  I didn't find any, however I did find a connection to earth that should not be there, so I cut the rail.  To my surprise the receiver came to life - a loud hum from nearby a/c cables, but the crackling of lightning was there to be heard.   

The first photo shows the first attempt on the left, with the second version functioning attempt on the right.  The second photo shows the back of the circuit.  My soldering is pretty messy, and in a few places in my haste I tore off the copper track with a cold solder joint.

I want to work out how to get my phone to record the output, but I am quite pleased I got it working before I went back to work.  

This electronics lark is kind of fun.  The next task is to get it a case.

 

[Alien 13]

Good job, now you have built one project the world is you oyster lots of cheep stuff out there to build.

Alan

[HN50]

1 hour ago, Alien 13 said:

Good job, now you have built one project the world is you oyster lots of cheep stuff out there to build.

Alan

Hi Alan,

Thank you.

Yes, I was thinking I could try some other projects, it has cost me less than I was expecting.

Though I might make the same receiver again just to make sure I didn't fluke it.

Dave

 

[HN50]

I bought a housing for it and squeezed everything in.  Not terribly elegant but at least it is now in a protective case.  Next time I need to think more about the length of leads for things like the headphone socket and switches.

Now I just need to figure out how to record from it.

 

[HN50]

I have been thinking about more about this and decided to make it again, except this time I would crunch it down in size.

I found an iPad app called StripboardCAD and used that to lay out the components.  The attached photo is of work so far.  That isn't a 2p though, it is a manhole cover.  I am using Soviet components.

Boom boom.

I have a metal case for it and will be using an aerial with a bnc connection as the previous attempt is not as robust as it could be.

The app also allows you to export a PDF of the circuit.  I have been in touch with the fellow who designed the radio and once I am happy it is working I was thinking of uploading it here. 

[HN50]

Free time today has meant I can get the radio finished.  The case is aluminium so not to difficult to drill, just a bit fiddly wiring up the potentiometer (it is a potentiometer switch combination, so there were 5 wires to keep track of)

I wanted to connect the case to earth as in the first attempt you needed to keep your hand touching a bolt, whereas if the whole case is earthed you just need to be holding it.  I soldered wire to a thin piece of brass and this sits between the potentiometer and case.  I also made a plastic 'shoe' that the circuit sits in to prevent any shorts from coming into contact with the case.  The bnc socket is an insulated one from maplins, while I bought a bnc aerial from eBay.

It looks a bit smaller and neater than my first attempt, though I can hear the battery moving a little so need to fashion something to hold it still.  I have been out in the garden and it does work, again over the mains hum I can hear the lightning clicks.  I am also pleased as I built straight off my plan as a test, so will upload that later.

All in all I am pleased.  It works (bonus!) and has a pleasing functional appearance.  I have the off work tomorrow so might try it out away from mains hum.

[HN50]

And this is the PDF for building the radio.  Some of the components are sitting a bit snug but I guess you could stretch the board lengthways to give yourself more space.

Dave

Peanut Butter VLF Radio.pdf

[HN50]

I have been using the radio for a little while now as it is quite nice to listen while off in the South Downs.  However the interference is pretty horrendous in my garden so I thought I would have a try at the version with the filter added to it.

I am awaiting delivery of a few polyester capacitors but this is work so far.  I have put together the plans in StripboardCAD and have been following them to the dot.  

I do rather like that massive fat 470uF capacitor, though it will make adding the potentiometer wires interesting.

[HN50]

As ever with these things I got the circuit wrong as it it didn't work.  Haha!  I also realised that the U.K. mains is 50Hz while the radio was set to filter 60Hz, so I am not sure it would have functioned as expected anyway.

I said I would build one of these radios for my nephew so I decided to try and design my own twin T notch filter and incorporate it into my earlier circuit plan.  

And use it as a test for my next iteration of the radio.

I went to the following website and used the calculation there to derive the resistor and capacitor values by means of an Excel spreadsheet.

http://www.radio-electronics.com/info/circuits/rc_notch_filter/twin_t_notch_filter.php

The filter has 4 resistors and 12 capacitors.  I then redesigned the layout in StripboardCAD so that the filter sits between the antenna and the IC input. 

I didn't quite believe it would work so retrofitted it into the first radio I made, and to my surprise it worked.  I could hear sferics but the mains hum was significantly reduced.  It took about 5 seconds for anything to be audible which I put down to the capacitors in the filter needing to charge up first(?).

Today I got to work on the actual circuit.  The circuit board is a bit shorter and wider than the previous one but still fits in the same case.  I also painted on a thundercloud from the weather forecast too for fun (good old Humbrol enamels).  

I am quite pleased as the filter is working.  It does not get rid of all the mains hum entirely but quietens it to a tolerable level. 

I'll post the updated plan later.  I have given up trying to record to my iPhone so instead I have downloaded spectrum lab and have started playing with that on an old laptop.

[HN50]

And here is the circuit plan.  Again, the fit of the components is a bit snug but you could always stretch the board lengthwise.  I think in the next version I need to do something about all the wires, possibly by fitting the potentiometer and on off switch directly to the board.

Peanut Butter VLF Whistler Radio with 50Hz notch filter.pdf

Edited November 27, 2016 by HN50
Extra comment

[HN50]

I had been meaning to compare the two radios before the version with the notch filter was sent off, so I quickly fired up Spectrum Lab and took the laptop outside into my garden.

The trace below is for the unfiltered radio at about 50% volume; any louder and it becomes uncomfortable.  Vertical lines are sferics with a few louder ones visible.  The horizontal lines up to about 6kHz though are the mains hum.

The next shot is the radio with the notch filter, volume at 100% which is quite pleasant to listen to.  Vertical sferics can be seen, but the overall mains hum is significantly reduced.  The filter is removing 50Hz (the bottom of the plot is black), but the harmonics (the diffuse purple band up to about 6kHz) still get through. 

I think, happy to be corrected. 

Whilst not scientific it seems to indicate the filter works. 

[HN50]

It has been a bit of a while since my last post.  I have tried again making another radio, but seem to keep messing it up somewhere.

I have decided to try and make a radio with individual transistors and have been looking around for the circuits and components for it.  That way I can make discrete radio parts and separately test they work.  

However it also occurred to me that if I am going to try and develop my own I need some test equipment in the form of a signal generator and an oscilloscope. 

I got one of those XR2206 signal generator kits and spent an hour and a half making it this afternoon. It was pretty simple and looks rather good in the Perspex case.  I am running it with a variable voltage transformer from Maplin.

After having built it I tested it by clamping the red out put to my radio antenna and the blue earth to the casing.  I then put on the headphones to listen, and was pleased to say that the roar from the mains was replaced by a high pitched whine that changed pitch when I moved the dials.

Next I wanted to see what it looked like when I connected the radio to the laptop and Spectrum Lab was running a trace.

The shot above is how the radio behaves inside and sounds even less pleasant.  However when the signal generator comes on it looks like the next shot.

I think the line at 4.5kHz is the frequency being generated by guestimation of where the knob is. At 3 seconds I twisted it which is what the fluctuations are.  I think though I am going to buy that oscilloscope kit other people have built to work out exactly what frequency the thing is producing as there are multiple lines in the trace.  

But anyway, at least the signal generator does something when switched on. 

Next is either the oscilloscope or a breadboard test bed.

[HN50]

It has been a bit of a while since I have done anything on this what with work and my attempts to detect SIDs with my laptop and a loop antenna, however I have been wanting to get back to it.  I had thought about trying to see if I could design one from scratch but in the end working with someone else's schematic would be more straightforward. 

I spent some time making a proper test bed for prototyping circuits as I had been trying to hold the breadboard in one hand, and antennas, volume controls, batteries and earths in the other.  I found some spare Perspex kicking around and made the thing below;

Everything is mounted in the board, and all you need to do is make sure you are touching the earth (the bolt on the left).

I have started making the BBB-4 by Stephen McGreevy as I would quite like to try a different design to the one I built before.  On its own it does not have an amplifier powerful enough to drive headphones, so I have also looked around for the circuit for this too.

The circuit in the screenshot works (I can hear that telltale spitting pan sound  ), though there is quite a lot of feedback on the volume.  

Anyway, I will look at that and if I can get it working I will turn it into another of those plans and post it here.

[Alien 13]

1 hour ago, HN50 said:

It has been a bit of a while since I have done anything on this what with work and my attempts to detect SIDs with my laptop and a loop antenna, however I have been wanting to get back to it.  I had thought about trying to see if I could design one from scratch but in the end working with someone else's schematic would be more straightforward. 

I spent some time making a proper test bed for prototyping circuits as I had been trying to hold the breadboard in one hand, and antennas, volume controls, batteries and earths in the other.  I found some spare Perspex kicking around and made the thing below;

Everything is mounted in the board, and all you need to do is make sure you are touching the earth (the bolt on the left).

I have started making the BBB-4 by Stephen McGreevy as I would quite like to try a different design to the one I built before.  On its own it does not have an amplifier powerful enough to drive headphones, so I have also looked around for the circuit for this too.

The circuit in the screenshot works (I can hear that telltale spitting pan sound  ), though there is quite a lot of feedback on the volume.  

Anyway, I will look at that and if I can get it working I will turn it into another of those plans and post it here.

Nice, its good to see a proper test bed..

Alan

[HN50]

4 hours ago, Alien 13 said:

Nice, its good to see a proper test bed..

Alan

Hi Alan,

Thanks for the post.  I have been experimenting with high and low pass filters this evening and I have to say that it all being mounted on a single rigid board makes it much easier to handle!

Dave

[HN50]

I have been working away and now have a functioning prototype.  I took the schematic for the bbb-4 receiver;

http://www.auroralchorus.com/bbb4rx3.htm

and married it to a headphone amplifier;

http://www.circuitbasics.com/build-a-great-sounding-audio-amplifier-with-bass-boost-from-the-lm386/

Which has given me something that looks like the following;

Looks ugly but does work.  The lower potentiometer is volume control, the upper is gain control.

I have also been playing around with an online filter designer and have added in a 230Hz high pass filter (try and take the edge off mains hum) and a 23kHz low pass (filter out long wave radio; without it you can hear voices  ).  As I mentioned earlier, I can't believe how much easier the test board makes things, as particularly with filters you can easily switch them in and out while the radio is working to hear the difference.

Next is to (once and for all) get it working with a spectrum analyser on my iPhone.  I have bought specially some 4 pole headphone sockets, so will hopefully get one working on the test board first. 

Dave

[HN50]

I have added a 4 pole socket to the test bed so that I can try and get the radio plugged into my iPhone and working with a (free-ish) app called SpectrumView.  I like SpectrumLab but getting out the laptop every time is a bit of a faff. So I added the socket at the bottom corner;

Black lead is earth, red microphone, white left and right headphones.  I am waiting for the silicone sealant to dry, however I very gingerly plugged it in and tried it in the garden...

The vertical lines are sferics.   There is a lot of hum from the mains, and I believe I can see three military transmitters at approx 18kHz, 19kHz and 22kHz but never the less I can now record to my phone.  I will try and take it somewhere more radio quiet in the South Downs as the small screen makes seeing stuff harder with the a/c hum, but otherwise I am quite pleased.  Just realised that the phone was not in aeroplane mode, I will try that as well next time.

At the moment the socket won't work with the headphones, however I am thinking of having two sockets on the finished thing; one for headphones, the other for recording. If I play some more it might be possible to have a single socket do both.

Dave

Edited August 3, 2017 by HN50
Grammar/no transmitters

[HN50]

I had a play this morning by rewiring the 4 pole socket to run from the second transistor rather than from the lm386 audio amplifier.  The BBB-4 is designed to plug into a recorder or laptop directly, however the visual settings on the iPhone spectrogram are basic and you can't alter the colour distribution to handle a weaker signal.  Anyway I wanted to see what the difference looked like;

Versus the plot from yesterday out the headphone amplifier;

I am sure this would not be a problem in SpectrumLab, but for the purposes of what I am trying to achieve I prefer the second.  So I think I will have the socket(s) out the headphone amplifier.

Dave

[HN50]

I have been playing around again with SpectrumView and I found that it does have a gain control in settings, so by adjusting it you can display a fainter signal better, as below;

I tried running it out the headphone amplifier again, however one thing I have found is that the plot does/can become a bit erratic  (overload/feedback? - limit of my electronics knowledge) as below;

So maybe it might be better to run any recordings from the second transistor as per the original BBB-4 design and have a dedicated radio for this (another project!).

I have also found that I can either run the headphones or the microphone at any one time. Again, probably a simple fix for someone with electronics knowledge but at this stage I am just happy to have a functioning radio. Given that this is intended as an audio project I have decided that the first iteration will just have a socket for headphones.

For the moment I have gone as far as I want with the prototyping, so I will fire up StripboardCAD and start laying out the circuit.

Dave 

 

[HN50]

I am still working on converting the schematics into a layout on StripboardCAD, but in the meantime I went out into the South Downs and a slightly more radio quiet location to try listening and recording with the prototype.

There is significantly less mains hum, though you can hear a little interference from longwave (I think) radio in the form of faint garbled speech.  However the low pass 24kHz filter is helping to remove some of that.

I played around with the gain on the radio and spectrogram, but the above is certainly better than in my back garden.

Tweaking the settings more and I could see quite a few more VLF transmitters (horizontal lines) from about 12kHz up;

I heard lots of sferics but no tweaks or whistlers, though I don't think midday is a good time to listen.  

The iPhone can be a bit temperamental in knowing when the the radio is plugged in, but my first version will be headphones only so I am not too fussed about solving this now.

Anyway, back to getting that circuit layout complete.

[HN50]

It has been a bit of a while getting the layout done, but I am starting to assemble the new circuit.  Have got the circuit board cut out and cut rails as per plan.  So I will get soldering tomorrow.

Not the most exciting of updates, but after a bit of a break due to work it is nice to see the build progressing again.

I am also keen to get the prototyping board cleared as I have started tinkering with an Arduino and have bought a data logging shield.