Table 1 Equipment list
OPAMP 082 (dual)
100K Linear Trimpot
Capacitor Electrolytic 220uF
Capacitor Electrolytic 47uF
OPAMP 741 (dual)
Audio Isolation Transformer
DIP-8 IC Socket
Capacitor Poly 1000pF
Capacitor Poly 220 pF
Capacitor Poly 100pF
‘T’ shaped connectors
Fig. 1 Circuit diagram
2.3.1 Building the on-board electronics
1. Connect the amplifier across the ends of the loop antenna with a terminal block.
2. Provide positive and negative voltage power for U2 with a 12V battery.
3. Provide zero point mid-way between the positive and negative voltage power a traditional 741-type op-amp.
4. Connect voltage point to the input of U1 which is wired in a voltage follower configuration.
5. Bring the output from the amplifier board to the PC soundcard using a 75 Ohm coax cable.
6. Isolate the cable against locally induced interference by a pair of audio isolation transformers at each end.
7. Build the amplifier on the breadboard and test it with the signal generator and oscilloscope.
8. Construct it permanently on a breadboard
Fig. 2 Finished on-board electronics
2.3.2 Building the antenna
Connect the pipes in such a manner where it is stable enough to support the cable.
Fig. 3 Finished antenna
2.3.2 Determining the natural resonant frequency.
1. Connect the oscilloscope probes directly across the open loop terminals.
2. Make a single loop of wire about the same diameter as the antenna and position it about 10cm distant and parallel to the antenna.
3. Connect the signal generator across the ends of the single loop of wire.
4. Set the signal generator to produce a sine wave at about 5kHz.
5. Measure the voltage induced in the antenna at that frequency using the signal generator and record it.
6. Increase or decrease the signal generator frequency systematically and record it.
7. Continue testing until it is possible to identify the natural resonance of the antenna by the peak voltage.
2.3.3 Tuning the antenna to the frequency of the VLF station
1. Decrease the resonant frequency, increase the value of the polypropylene tuning capacitors connected across the ends of the loop.
2. Connect the tuning capacitors at the tuning stage with crocodile clips and breadboard.
3. Place the capacitors in parallel on the breadboard to build up the value you need, and then link them to the antenna ends with test wires terminated in crocodile clips.
4. Repeat the test with the signal generator to find the resonant frequency until reaching the desired frequency.
5. Finalise the construction of the antenna.
6. Connect the antenna to the terminal block that is on the breadboard.
2.3.4 Setting up the radio telescope
1. Point the antenna in the direction of the transmitter
2. Choose a site that has the least local interference
3. Mount the antenna and fine tune the orientation of the antenna.
4. Connect the system to the PC soundcard.
2.3.5 Installing the PC software and finding the signal
1. Digitalise the signal received at the sound card.
2. Measure the VLF frequency of interest.
3. Produce charts of power against time by graphing them.
2.4 Risk assessment and management
It is advisable to avoid going into the rain to repair the systems, should any of them malfunction.
- Electrocuted by electric in power socket
- Antenna struck by lightning while we are holding the other end of the antenna
- Electrocuted by broken wire
- Burnt by Soldering
- Cuts and bruises
- Cuts when sawing
2.5 Data Analysis
1. To test whether it is working
2. To test whether it can capture a solar flare
3. To check whether our data matches the NASA data.