Mobile Directional Lightning Detector

I have discovered that lightning causes interference to AM radio receivers from a great distance. This is due to the way the AM recievers operate, Amplitude Modulation, and the spark of lightning causes a wide band pulse of energy around 500Khz. This means that while I am out chasing storms, I can listen to the AM radio around 530Khz, and determine the relative activity of the storms around me.

The interesting part of this, I can use the radio to listen to a storm even though it is not producing Cloud-To-Ground (CG) lightning. The radio can also recieve the Cloud-To-Cloud static discharge as well. The only problem is the radio and antenna of the car is Omni-Directional (I receive the signal from all directions), so I cannot use the radio to determine where the stronger storms are around me.

I started looking online for Lightning Detectors, and what commercial products I found were either expensive, not informative. There are some portable lightning detectors on the market that will estimate the time a storm will arrive, based on the same AM Pulses. Other detectors are dependent on a computer with expensive software, and it uses other similar stations to triangulate the location of a lightning strike.

I started thinking about Doppler Shift Radio Direction Finding, and even asked a local Elmer if I could use the same technology tuned for the 144MHz band on the 500KHz lightning pulses. This was ruled out due to the need to adjust the antenna size and spacing to achieve what I wanted to do, making this a non portable project.

Directional Lightning Detector
below my mobile HAM Radio
APRS and NOAA WX

The Elmer did suggest an alternative technique for radio direction finding, and that was to use the signal strength. This is what most people do when they first go Fox Hunting (Radio Direction Finding), they put a handheld radio against their body, and while rotating, they observe the signal strength meter. Using the body as an attenuator, you find the dip in signal, and the signal is coming from directly behind you.

I came to the conclusion that I could build four Lightning Detectors, and build a four element antenna so I could determine direction of lightning activity. I found some diagrams online for Lightning Detectors, and placed a parts order with Mouser.

I started building the recievers into a box, and used a 5v regulator for each receiver. I had some issues with two of the receivers, and that required some troubleshooting and replacing a few blown components. I also noticed some interactions between the receivers while testing, so I added a diode to the ground of each reciever and that seemed to isolate the recievers from each other.

Built receiver box

I salvaged an IDE connector from an old motherboard and used a computer case wiring harness to enable me to disconnect the front panel lights to work on the unit if necessary. While I was building the units, I added the Red LEDs to each receiver for testing purposes, but I didn't bother to remove them once complete.

Bearing indication of lightning

Testing each receiver is easy, simply take a multimeter on conductivity test, and when you test between the GND and the antenna lead, the circuit should activate the LED for a moment. The lightning simulator from TechLib is also useful, but a similar can also be done with a BBQ sparker or an Aim-N-Flame. A small spark will cause a similar burst of interference as a bolt of lightning. Because of the small size, the sparker test stops working when more than a foot away from the antenna.

Next, I started building a simple antenna array for the recievers. I used a tupperware container, and wrapped cardboard with aluminum foil.  I double stick taped the foil so it would stay on the cardboard. I created a small channel under the bottom square, so I would not damage the RG-174/U Coax. I placed two hard drive megnets inside the case, under the base square of the antenna, so I could Mag Mount the antenna to the top of my car.

Ground wire, and magnets on bottom

Before securing the base of the antenna to the case, I poked a hole in the center of the case, and ran a ground wire. This would allow the antenna to use part of the car as a ground plane. This might not be the most efficient design, but I am not transmitting with this unit, only recieving.

Antenna Elements

Next, I started building the ellements. I took the ground from each coax, and soldered them together in the center. I added the cross to isolate each antenna. This design would give me an eight way direction of the storm, in theory. I also added a ground wite to each of the crosses, and soldered it down onto the base. I checked that I had a good ground with a multimeter. Next, I took a few feet of wire for the element and attatched it to the cross with more stick tape.

Here is the completed antenna. Now if I can just get people to accept it, instead of yelling at me, while driving 70 MPH, that I "have something on the roof". I think a gray can of spray paint should do the trick.

Now if I can just get a few thunderstorms in the area.

Ed KI6PSP http://KI6PSP.blogspot.com

FM Radio Broadcasts on Apple Products

iPhone 4 and the iPad 2 has an FM Receiver and an FM Transmitter. But don't expect to be able to record your local radio station, or transmit your tunes wirelessly to your stereo in the car. According to a complete tardown by ifixit.com, the iPhone4 and the iPad 2 uses the Broadcom BCM4329 for connectivity. It boasts 802.11N with Bluetooth® 2.1 + EDR AND FM (TX AND RX).

Do a quick Google search, and you will find a lot of apps that will let you listen to the radio, however none of them will be using this hardware feature, all of them will be internet radio. Its a shame that Apple locks out features like an FM Receiver, and a Transmitter, all in the name of maintaining its iTunes Marketplace. What is really disturbing is, the 2nd Generation iPod Touch, iPad, iPhone 3GS, and all of the newer versions of what I just listed, all have the capability in the hardware to at least receive FM radio broadcasts.

This shows that Apple has the capability to make their current products better, but wont enable those features because of fear it would hurt its profits on iTunes, not to mention opening a new can of worms over DRM. I remember recording FM radio onto cassettes, what happened to those days? Its not like it is completely banned, after all, I have a voice recorder with an FM receiver, that records directly to MP3.

And Apple wonders why people jailbreak their devices....

Ref:

iPad 2

http://www.ifixit.com/Teardown/iPad-2-Wi-Fi-Teardown/5071/2

http://www.broadcom.com/products/Bluetooth/Bluetooth-RF-Silicon-and-Software-Solutions/BCM4329

iPod Touch (2nd Generation)

http://www.ifixit.com/Teardown/iPod-Touch-2nd-Generation-Teardown/586/2

http://www.broadcom.com/products/Bluetooth/Bluetooth-RF-Silicon-and-Software-Solutions/BCM4325

iPhone 3GS

http://www.ifixit.com/Teardown/iPhone-3GS-Teardown/817/2

http://www.broadcom.com/products/Bluetooth/Bluetooth-RF-Silicon-and-Software-Solutions/BCM4325

iPad (1st Generation)

http://www.ifixit.com/Teardown/iPad-FCC-Teardown/2197/1

http://www.broadcom.com/products/Bluetooth/Bluetooth-RF-Silicon-and-Software-Solutions/BCM4329

--
KI6PSP (Ed)

Diamond X-50A

After a brief trip to the local HRO store (Burbank), the wife let me purchase a Diamond X-50A antenna. I wanted an antenna with a good amount of gain that was pre-tuned and I wouldn't have to mess with. I did think about getting the longer one (X-70A) with more gain, but I didn't want the variables of the multiple peices, hence the pre-tuned I was looking for. After installing it, it performs noticeably better than my stacked J-Pole antenna. I do see the improved radiation pattern from across town, with a higher S meter reading on my radio. I think my longer J-Pole had slightly better receive gain, but not as effective of a radiation pattern. Overall, I am very happy with it. -- KI6PSP (Ed)

Strange Repeaters throughout Town

This is what I am attempting to identify

Screenshot of my map.

I have worked to figure out what these are, and I believe they repeat data from our Gas meters by PG&E. On one of these boxes, I found a "Star" logo, and I found the same logo on the Smart Meter on my Gas Meter. These operate on 462.4125 MHz FM. Most of the repeaters are tethered to a street lamp, and supplied power from the light itself. One however is completely solar powered, so it must be something that is not heavily used or very low power output. I will attempt to gather more information, and locate others.

Here is my map of the boxes I have located:
http://maps.google.com/maps/ms?ie=UTF&msa=0&msid=106058093228991479326.0004904f367952e04491a

iPhone4 Antenna Problems

When you touch a bare antenna, you become part of the antenna and change the intended length of it. You will effectively detune the antenna, and reduce performance. I thought about this when the iPhone4 was announced, and assumed that they would insulate the antenna with some type of laminate, or plastic coating, I was wrong. I do think the design of the antenna is rather brilliant. Its designed to work when you hold it vertically or horizontally, but that goes out the window when you detune it. The Death Spot on the iPhone4, is basically shorting the 2 radios together. I wonder if you disable the Wireless and Bluetooth, if that problem will still be present. Apple's solution of giving out cases should have been from the beginning. I see this as poor research, development, and lack of proper field testing.

When they were Beta testing these in the field, the one Gizmodo found had a case to hide what it was. That case insulated the antenna. So their field testing results were flawed. I wonder if the engineer that designed the antenna was fired or not.

Antenna Polarization Demo

One of the most interesting Ham Radio related demos I have seen was done by Mike Herr (WA6ARA). He presented a demo of antenna polarization. He setup a small dipole (partially assembled Arrow Beam) to transmit 5 watts on 2 meters, while he had someone assist him by holding a custom dipole. The custom dipole was a simple foil wrap on a stick, with a small incandescent light bulb connected between the two elements of the dipole. Mike had his assistant hold the custom dipole about half a foot away from his Arrow dipole while he transmitted from his radio. When close and vertical, the light surprisingly burned bright. When the custom dipole was rotated, without changing distance, it quickly went dim, to almost completely out around 45 degrees, and nowhere close to bright around 90 degrees. This was a perfect example to demonstrate one of the FCC Questions in the Tech class pool.


T9B08: What can happen if the antennas at opposite ends of a VHF or UHF line of sight radio link are not using the same polarization?

A. The modulation sidebands might become inverted
* B. Signals could be as much as 100 times weaker
C. Signals have an echo effect on voices
D. Nothing significant will happen

This also makes me think twice about standing near antennas.

Ed
KI6PSP
http://KI6PSP.blogspot.com