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HN50

VLF radio receiver build

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This is today’s work, about 3 hours of soldering.  I think once again I have made the layout too snug (the inductors were a bit of a squeeze to get on), but otherwise so far I am pleased.  Will stop now as I am starting to make mistakes, but the next job is getting the flying leads on to the potentiometers and battery holder.

B3A4E301-D4EC-4269-A3DD-9373A2A9B4E6.jpeg.ec883bfabd440afcd5079cb47642d020.jpeg

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After more than a lot of frowning the radio is now 90% working (I wired the capacitors up wrong so both controls work backwards).  

I have also had to spend more than a bit of time debugging the circuit as I now realise the board had several important ommissions and would not work.  Mainly the +9v line to the op amp was going to the wrong leg.

A little reminder to myself of what happens when I rush or don’t pay attention.  But then again I have had voltmeter out comparing values to the prototype and also checking connectivity so it has been useful practice.

96A25D2A-E9D4-45B0-9B4C-EDB6ADA1BE50.thumb.jpeg.e0d7bbe550107e77b548ce811cabf30b.jpeg

I have a few days off this week so I will sort the potentiometers and insulate the underside of the board. And maybe make that second headphone socket do something.  

That case looks huge!

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After a bit of work today the potentiometers got sorted.  Well, they took 10 minutes to change, the following 2.5 hours was me trying to work out why the radio had stopped working.  In the end I traced to it a loose connection caused by me tugging on one of the leads.  I had plans to make a nice insulated shoe for the circuit and battery to sit in, but in the end I opted to use silicone sealant and glue them in place. 

Further down the line I am going to redesign the circuit so that the potentiometers are soldered directly to the veroboard, but I am happy enough for this version to have flying leads all over the place.  Anyway, this is the latest pdf after some post build changes;

BBB-4 VLF radio with headphone amplifier.pdf

I have compared the physical size versus the first one I made, and I think the boards are comparable in size, looking at it now I just needed the larger case be able to handle two potentiometers (left pot is gain, right pot is on/off and volume).  So if the amplifier was given a fixed gain, it would be possible to squeeze it into the smaller case.

IMG_1182.thumb.JPG.53a323cfbc4dd4b80ebc52e505209a31.JPG

I also have fired up SpectrumLab in my back garden to see if me messing about with filters has made a difference (the BBB-4 with the filters certainly sounds more pleasant than the unfiltered Peanut Butter VLF radio).  First screen capture is the unfiltered peanut butter radio;

59f0c743beb09_Unfilteredgrab2.thumb.jpg.60f68b03a0a784e1dff6da86b19ab092.jpg

Mains hum is very obvious right at the bottom of the plot, and it really overpowers all but the loudest sferics when listening.

The BBB-4 with high pass filter attenuates a lot of this (little signal below 1kHz).  There are still harmonics, but they are not as loud.  Gain is set to minimum. 

59f0c76b3d2eb_Filteredgrab2.thumb.jpg.5ee4a0aae430d887f24f9596e146f5d8.jpg

From a visualisation point of view the filters do not seem to make much of a difference, but for ease of listening they do.

Both plots show sferics (vertical lines), VLF transmitters (solid horizontal lines), and I think the intermittent horizontal lines are Russian Alpha transmissions.

So, all in all I am quite pleased.  I have a few ideas for how I want to improve the layout in future versions, but for the moment I will leave it as is.  The next stage is to clear the prototyping board as I want to put together a version of this radio that is tuned to just one of the VLF transmitters.  That way I can see if I can get the variation in voltage logged by an Arduino datalogger and use that for SID detection.  So the radio and filter will be posted eventually here, but I might start a separate Arduino data logger thread.

Hope you enjoyed the post.

Dave

Edited by HN50
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24 minutes ago, Alien 13 said:

Great project, well done..

Alan

Hi Alan,

Thank you.  It has been quite a slow piece of work but I have enjoyed it.  

Dave

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Another slightly underwhelming update approaching, but I am feeling a bit chuffed.  :)  I have been learning how to program an Arduino ('Exploring Arduino' by Jeremy Blum) and have been able to;

1) Detect a varying voltage (used a spare potentiometer)

2) Get time from a real time clock

3) Log results from #1 and #2 to an SD card every minute

4) Use a transistor as a switch to turn on an LED

My thinking is that if I can master all the above I have the basic ingredients for my logging module.  Today I have been trying to get #4 modified to turn a radio on and off; the bit in the red box below is the transistor switch (2N3904 transistor).  I gather these can take a maximum of 200mA - the radio seems to draw 150mA so I think it might be okay. 

IMG_1188.JPG.a64fb5555e33ed0fbc96388bd0f0174a.JPG

Anyway, I got the radio hooked up to spectrum lab and several weeks of work/frowning gave me this;

5a1086f0cd4ef_Radioonoff.thumb.jpg.5bb8a2a422c58eb1d4f065aa5994cbe7.jpg

The radio comes on at ~57.75 seconds, is on for a second, then goes off.  :D  Hahahahaha!

A little underwhelming, but baby-steps and all that.

Next I will try tinkering with the radio output so that it goes into the Arduino and gets logged, though at the moment I am trying to get the new version radio laid out and the narrow band filter working.

Dave

 

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7 minutes ago, HN50 said:

Another slightly underwhelming update approaching, but I am feeling a bit chuffed.  :)  I have been learning how to program an Arduino ('Exploring Arduino' by Jeremy Blum) and have been able to;

1) Detect a varying voltage (used a spare potentiometer)

2) Get time from a real time clock

3) Log results from #1 and #2 to an SD card every minute

4) Use a transistor as a switch to turn on an LED

My thinking is that if I can master all the above I have the basic ingredients for my logging module.  Today I have been trying to get #4 modified to turn a radio on and off; the bit in the red box below is the transistor switch (2N3904 transistor).  I gather these can take a maximum of 200mA - the radio seems to draw 150mA so I think it might be okay. 

IMG_1188.JPG.a64fb5555e33ed0fbc96388bd0f0174a.JPG

Anyway, I got the radio hooked up to spectrum lab and several weeks of work/frowning gave me this;

5a1086f0cd4ef_Radioonoff.thumb.jpg.5bb8a2a422c58eb1d4f065aa5994cbe7.jpg

The radio comes on at ~57.75 seconds, is on for a second, then goes off.  :D  Hahahahaha!

A little underwhelming, but baby-steps and all that.

Next I will try tinkering with the radio output so that it goes into the Arduino and gets logged, though at the moment I am trying to get the new version radio laid out and the narrow band filter working.

Dave

 

Impressive, you will learn lots from this project..

Alan

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5 minutes ago, Alien 13 said:

Impressive, you will learn lots from this project..

Alan

Thank you Alan.  Working with Arduino is rather fun, it feels a bit like old school programming when getting it to interact with home brew electronics.

Dave

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I am somewhat new to all of this. I am working on a loop antenna. I built a function generator (XR2206) to produce a "standard" signal for testing. Also I but together a frequency counter based on Arduino. I have been "playing around" with these circuits along with Spectrum software. Very interesting !

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1 hour ago, emirror6 said:

I am somewhat new to all of this. I am working on a loop antenna. I built a function generator (XR2206) to produce a "standard" signal for testing. Also I but together a frequency counter based on Arduino. I have been "playing around" with these circuits along with Spectrum software. Very interesting !

Hi,

Thanks for the post.  

Unfortunately, a whole load of non astronomy things have gotten in the way of my work on this since (Gulp! Can’t believe it...) last November.  

I had been having a bit of trouble building a band pass filter to tune to a single station.  It should be a case of a high pass and a low pass in series, but I think that something was not quite right with my workings, and I was investigating a different radio entirely.  Anyway I am hoping to get back on to this soon, and if nothing else I have a hankering to build a table top VLF radio.

Out of interest, what range of frequencies can the Arduino frequency counter detect?

Dave

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On 25/10/2017 at 19:33, HN50 said:

 

Dear Dave.

I have had really good experiences with you take on the peanutbutter vlf reciever and are now trying to build the bbb-4 with headphone amplifier. I'm not that strong in electronics yet, but your post are helping a lot, so big thanks for that!

I have a few questions that you might be able to answer? What is the potentiometer values and are the inductors really 0,1H? They are somewhat hard for me to find and pretty big compared to you images.

Best

HB

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On 08/05/2019 at 19:05, HB1 said:

Dear Dave.

I have had really good experiences with you take on the peanutbutter vlf reciever and are now trying to build the bbb-4 with headphone amplifier. I'm not that strong in electronics yet, but your post are helping a lot, so big thanks for that!

I have a few questions that you might be able to answer? What is the potentiometer values and are the inductors really 0,1H? They are somewhat hard for me to find and pretty big compared to you images.

Best

HB

Hi HB,

Firstly apologies, I only just saw that you posted on this thread.  I have been away from the site looking at programming with Arduinos and building my own, so the VLF has taken a bit of a back seat for the moment.   So I hope a late reply isn’t too late to be of use.

The potentiometers are both 10k.  I think though I had a dual gang 20k kicking around and wired it up in parallel. 

With regards the inductors, they were definitely both 0.1H.  Without wanting to sound cheap but I get my components from eBay :).  If you search;

Radial Ferrite Choke Inductor 10uH to 100mH
 

That returns several vendors (I am not connected to any).  
There are a few bbb-4 schematics out there and one lists them as being 82mH instead if that is easier to source.

63CF66A3-11C4-4188-A9AA-CFE47686C0FF.jpeg.727a23ae9c326db66273d46047378fb0.jpeg
That isn’t me in the text.

Once again, hope this isn’t too late to be of use.  Otherwise, thanks for the post and glad some of the stuff has been of use. 

Dave

 

 

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