“Welcome to the Brave New World – you had better be brave!”
You came here looking for knowledge that has been hidden from your eyes. You’ve come to the right place.
The first future tool I will show you is called Sonic Radar. This is way of detecting vehicles and aircraft far beyond what normal senses will allow. It takes only an afternoon to make the simplest form of this radar and $100. This demonstrator will detect single engine aircraft out to 7 miles, large trucks out to 12, and dual engine turboprops out to 30 under optimum conditions. You can download the instructions here as a .zip – and share (not copyrighted).
How Does It Work?
Every vehicle, be it an aircraft or ground transport, creates a wake of specific sound frequencies as it moves. These signatures can be clearly seen in real-time by using a waterfall projection program (provided free here), a laptop, and a sub-woofer converted to an amplified microphone.
This system comes in a range of sizes and capabilities. From a single microphone demonstrator to an integrated vehicle detection system that can cover thousands of square miles. The Type I demonstrator provides detection and approximate distance only; a Type II system can give you a rough bearing of the sound source, as well.
Let’s talk Decibels. This is a logarithmic unit of measuring power. To say something has a 3 Decibel (dB) rise in strength is to say it has doubled in its power. A 6 dB rise is 4 times the original strength. A 10 dB rise is 10 times.
The basic Type I demonstrator will provide 27 dB over your normal hearing in the range of 100 Hz to 600 Hz – where the majority of vehicle signatures are located. Type II can amplify 35 dB, Type III 42 dB, and a Type IV system up to 49 dB.
To put his into perspective, let’s say something is generating a 100 Hertz (Hz) sound and you can barely hear it at one mile. A Type I system will see it on the waterfall graph at about 12 miles, assuming line-of-sight. A Type II at 20 miles, Type III at 28 miles, and finally the Type IV system at 37 miles.
There’s a dB loss that happens, of course, due to distance. That’s the inverse-square law. There’s also air attenuation – air absorbs the sound energy and this is dependent upon temperature and humidity. In general, the lower the temperature and higher the relative humidity the better sound travels.
As frequencies go up the air attenuation goes up as well. What this means to you is a lower-frequency sound (like a motorcycle) can be detected far out, yet a higher frequency source (like a micro drone) must be much closer – in addition to its lower power output.
As vehicles come towards or away from you there is Doppler Shift. For a prop-driven aircraft this difference may be around 100 Hz.
Here’s a table describing what detection ranges you can expect for common vehicles and sound sources:
Wind and ambient noise levels can interfere with detection. In general, this system provides the best sensitivity below 10 mph winds and in a rural environment. It can still be used, however, in a noisy urban area with the right settings in Spectrum Lab (the program used to display the sound sources).
A note on using a woofer as a microphone. Most woofers are 4 Ohms impedance, and you may wonder about connecting into an audio amplifier which is expecting much higher impedance. There’s no issue. I’ve experimented with a pile of audio matching transformers and nothing works as well as directly connecting the woofer to the amp. An example of what you were taught in school departing from reality.
BUILDING A TYPE I DETECTOR
Parts and Procurement
1 12” Sub-Woofer, 4 Ohms Impedance
1 1.5 KOhm resistor
1 1 uF Capacitor, Tantalum or Equivalent (Not Electrolytic)
1 Audio Amplifier, Radio Shack 32-2056 or Equivalent
1 Audio Cable, 25’, with 3.5mm Mono Audio Male Plug Adapter
1 Audio Cable, 6’, RCA Male to 2.5mm Male Stereo Plug
1 Set of Headphones, 2.5mm plug
A note on procurement. Always purchase these items with cash. Some vendors (like Radio Shack) have an aggressive “know your customer” program in partnership with the Feds. They will ask for a phone number or an email address. Make up one in your mind beforehand and give them that. Smile and be polite. Leave your cell phone at home when you go out purchasing these items.
1) Strip one end of the 25’ audio cable, leaving the woven shield and center conductor. The other end should have a 3.5mm male plug adapter.
2) Connect the woven shield ground to the (-) terminal of the woofer.
3) Connect the center conductor to the (+) terminal of the woofer.
4) Connect the audio cable to the amplifier “microphone in” jack with the 3.5mm plug.
5) Connect the 6’ RCA audio cable to the output of the amplifier. You will be using only one channel, either Left or Right – your choice.
6) Cut the 6’ audio cable in half. Strip the newly formed ends for 1” leads. Solder in the filter as shown:
7) Wrap the filter in electrical tape, ensuring the leads won’t short.
8) You should now have a cable coming from the amp output with a dongle in the center containing the filter, and the end of the cable should be a male 2.5mm stereo plug.
Installing Spectrum Lab and Testing
1) Download Spectrum Lab
2) Unzip to your desktop
3) Install the program
**NOTE** if you plan to use a computer that will be connected to the Internet for this project be aware Spectrum Lab communicates back home. Use a program like ZoneAlarm to selectively block this program from Internet access (unless you want to get audio data from remote Sonic Radar sites via TCP-IP, as part of an integrated detection system which is discussed later).
4) Test the internal microphone in your laptop by trying to record and playback sounds using Microsoft Sound Recorder (installed on all versions of Windows). Don’t proceed until you are successful at this.
5) Right-click the speaker icon in the lower right and select Recording Devices (or Properties for some computers).
6) You will have to dig around the microphone properties to find the “microphone boost” check box. Check that box. Every sound card driver seems to be different and not all offer this enhancement.
7) Run Spectrum Lab.
Under the top tab “Start/Stop” ensure the Start Sound Thread and Audio Input are checked
Under the top tab “Options” Select Audio Settings. In the upper left corner ensure your sound card is selected as an input device.
8) Plug in your headphones into the headphone jack on the computer. Most computers will allow you to monitor what comes into the microphone port.
9) Turn on the amplifier.
10) Set the amplifier to “3” and plug into the microphone input on the computer. You should see a change in the waterfall display. If the computer asks if this is a microphone or line-in, select “microphone”.
11) If there’s no change in the waterfall display try adjusting the brightness and contrast slide bars on the far left center of Spectrum Lab.
12) If you still see no “static” or signatures on the display then begin to increase the volume on the amplifier.
13) Adjust the frequency bar at the top by right clicking it. Select “Zoom out by 50%” and then drag your mouse over it to the right until it shows the range of 0 Hz to 600 Hz. You are now ready.
If you aren’t able to make the system work, here are some things you can look at:
- Plug in a desktop microphone and see if making sounds shows up – if so, then there’s an issue with the woofer / amplifier / filter chain.
- If the desktop microphone doesn’t make a change in the waterfall then take a look at the settings for the microphone input in Windows. There may be a volume adjustment or mute checkbox that is misconfigured.
- A 60 Hz hum means a bad ground somewhere. Connecting the amplifier ground lug directly to the building grounding rod helps immensely. Also, connecting the amplifier output shield wire to physical ground also helps.
- Take some time to get to know Spectrum Lab – check out the tabs, look around. Be warned, however; some changes can’t be easily undone, so if in doubt, just reinstall the program. I’ve found that making the FFT input size 262144, the soundcard sample rate 48000, and the waterfall interval at 1000ms works well with my system.
Below are some signatures for common ground and air vehicles:
Four Engine Turboprop:
Single Engine Private Plane:
Large Dual Turboprop:
Dual Engine Private Plane (Skymaster):
In time you will become familiar with the patterns caused by vehicles. During operation you will be using the brightness and contrast slide bars to ferret out those patterns.
First contact will most likely be seeing a line appear on the waterfall. Shortly thereafter you may hear the vehicle in your headphones and determine what kind it is.
Wind can be problematic. However, there’s usually breaks in the wind where signatures will show up – be patient.
Aircraft generally provide sweeping lines on the waterfall diagram. Ground vehicles can be somewhat erratic. Micro drones are in the upper band and can be erratic as well.
An aircraft orbiting around your location (like a drone) will make a long vertical sine wave on the display, the period of which may be a couple of minutes. That’s a real bad sign. This is true of a circular flight path or a figure-8.
Beware the Siren’s Song!
Long nights at the prepper CQ are bound to cause anxious thoughts, especially after TEOTWAWKI. In your headphones you may hear voices, faintly, coming in and out of the static. Don’t panic. It’s not the ghosts of the millions of welfare voters who perished in the cities. It turns out this system occasionally catches short-wave transmissions.
ADVANCED DESIGNS: TYPE II – TYPE IV
Type I assembly was presented here as the following systems have similar construction.
The Type II system consists of four woofers at the ordinate points. The sensor array of woofers is constructed simply of a 4’ x 8’ plywood sheet cut into two 4’ x 4’ squares. 14” x 1” boards go from each corner, making four triangular sections. The woofers are placed in these sections, pointed out, and fastened. The remaining 4’ x 4’ plywood square is then screwed on the top, making a sandwich, if you will, of the woofers. All wood pieces need to be painted or stained and the entire assembly elevated a foot off the ground with posts.
To abate noise and wind you will need to staple the thick evaporative fabric from a swamp cooler to the sides of the sensor array. The best material is synthetic (the blue kind) and can be had at most hardware stores.
Use shielded audio cable throughout the construction of the system and properly ground the amplifier. Drive another grounding rod if you have to – I did.
The woofers are then connected to four separate amplifiers and filters. The outputs of these are then connected to a surround-sound speaker set (~$70). The central output of the surround sound system is connected to the laptop microphone input. This sums the four inputs so Spectrum Labs sees in all directions. YOU are the direction finder in this setup – arrange the speakers equidistant around you for best effect and make sure each speaker is aligned with its woofer outside – North to North, South to South, etc.
An alternative to a surround sound system is surround sound headphones. Skull Candy makes a set, the only requirement is they are able to take analog inputs. Most surround sound headphones use USB inputs.
This is essentially the Type I except the woofer is placed at the focal point of a C-Band antenna. You may want to make a weather-proof box for the woofer. Be careful not to aim the antenna where the Sun may pass at any time of the year; it will ignite the woofer. A layer of heavy aluminum foil over the front of the woofer should protect it.
Type IV and Integrated Vehicle Detection Systems
This system offers the best range and can be a crew-operated system. It is essentially a Type II with massive (8’ x 20’) collectors. The woofers need to have a feed horn – the quad section from a Type II would work well. The reflectors are parabolic sections that can be made from plywood. The outside of the building needs to be sheathed in canvas and painted to look “normal”.
Spectrum lab comes with an I/O functionality where one station’s audio inputs can be transmitted to another user. Look under the AD/DA Server Tab in Configuration. This would allow for an unlimited number of Sonic Radar stations to report to a central location – each remote station would need a corresponding instance of Spectrum Lab running at the central location.
The link between these remote sites could be via ad-hoc Wi-Fi or VPN Ethernet connection.
By using two 2’ satellite dishes and a Wi-Fi USB dongle, you can easily construct a Wi-Fi link stretching up to 12 miles or more. I would suggest ad-hoc and encryption as well. These antennas do not need to be outside; a good link may be possible by placing the antenna inside an attic. This keeps the weather and prying eyes away.
The next iteration will automate the detection and bearing based on a Type II system