Solar Maximum

The sun is approaching its 9-14 year (approximately 11 year) solar maximum.  There will be an increase in sunspots and large solar flares.  Sunspots are areas where the sun's plasma gets caught in strong magnetic fields and stops circulating, so it cools and gets darker (relatively speaking) on the surface.  The flares affect the earth's ionosphere and can cause radio signals to reflect and travel further around the earth than normal. 

We made a first pass at a sunspot viewer.  Here there is a pin hole in a sheet of aluminum foil with a tiny image of the sun falling on the sheet of paper below.  Effectively a simple pinhole camera.  The sun's image is there, but is too small and faint to see any details.

Anyway, this is just a first pass.  We will see what else we can come up with.

The solar activity effect on radio is supposed to be especially strong in the 10 meter wavelength.  To look into this I made a half-wave dipole antenna under our back porch roof.  It just fits if I angle it diagonally.  It is made of two 16 gauge bare copper wires cut to the right length, soldered to a coaxial cable, and suspended with jute fiber.  The length, 1/2 a wavelength, should make it more sensitive to the 10 meter band because of resonance.  Along a full wavelength the wave travels from its "highest" to its "lowest" in the middle and back to its "highest" point at the other end.  A half-wavelength reaches from the lowest to highest part of the wave.  This antenna has two 1/4 wavelength sections.  When one side is at its lowest the input from the other side should be at the highest, maximizing the difference detected in an signal from 10 meter wavelengths when the coaxial cable is plugged in. 

New Year's Dinner in Hawai'i

In our family it is traditional to have pork (preferably hog jowls, but we haven't found that in stores in years), greens (preferably collard) and black-eyed peas for New Year's Dinner for luck in the new year.  The greens represent making money and the peas coins.  We couldn't find some of the ingredients so we made a twist on the recipe this year.  V cooked pork laulau.  It has pieces of pork, wrapped in taro leaves (for the greens), in turn this is wrapped in Ti leaves for cooking.  Below you can see the laulau placed on foil with holes in it for steaming from the pot of water below.  Also, we could not find any black-eyed peas so we used black beans as a substitute, which can be seen cooking in the pot at the rear. 

 The ti plant (ki in Hawaiian) was spread across the Pacific and brought to Hawai'i by the Polynesians.  It is used for lots of items in traditional Hawaiian culture and planted next to a house today for good luck.  The people that rented our house before us, that I met briefly, were Native Hawaiian and left a ti plant for us in a pot.  I planted it in front of the house below. 

AM radio check

I was up last night from all the fireworks and commotion.  I read that AM radio travels further at night by skywave so I checked what kind of reception I could get with the radio in our van, and also as a future check for our homemade radio reception.   Here is a list of the radio stations in Hawai'i.  And here is a site that will give the coordinates of the radio towers.  I was able to tune some kind of signal from all the AM stations on the islands except for one, KHLO in Hilo on the big island.  Many of the stations in Maui and on the big island were not intelligible.  However, I was able to tune in one station from Maui that was clear, and two stations from Kaua'i that were clear.  Here is a map (click for a larger image).

Icons in black are stations I picked up with the foxhole radio (during the day).  Blue are stations with clear reception from the van radio at night.  Red are stations with unintelligible reception on the van radio.

One station was unusual because it only had a three letter call sign, KGU.  I looked it up and KGU is Hawai'i's first and oldest radio station.  It went on the air in 1922.  It was used as a homing beacon by Fred Noonan (of Amelia Earhart fame, he was the navigator on their around the world flight when she disappeared) in survey flights of the Pacific in 1935 and by the Japanese in 1941 to lead them to Pearl Harbor at the beginning of WWII for the US. 

As an interesting aside, the first attempt to fly to Hawai'i was made by John Rodgers in 1925.  The plane landed in the sea and he had his crew make sails from the wings.  He sailed for 9 days and made it to Kaua'i. 

One surprise was a signal at 1700 kHz.  It was borderline intelligible.  The signal would get stronger then fade into static then come back.  At one point I clearly heard "ESPN Radio."  The nearest station broadcasting at 1700 kHz is in Mexico at the Tijuana border, XEPE-AM, and sure enough it broadcasts ESPN sports radio.  I also read that AM stations at higher frequencies are more likely to have long distance propagation.  It is 2,600 miles away.  This is equivalent to picking up the same station in Tijuana from Quebec City, Canada. 

View Larger Map

In fact here is a post about picking the station up from Ottawa, Ontario. 

Foxhole Radio Modifications

I played around with the foxhole radio we made earlier to try to increase the signal.  In a traditional foxhole radio a single diode is used, which cuts off half of the AC from the signal and converts it to a useable audio wave.  This is a half wave rectifier, which does not make use of all the power potentially available in the signal.

I used four LEDs hooked together in a diode bridge to make a full wave rectifier where current flowing in both directions in the signal are converted to an audio wave. 

Here is the actual setup.

And a closeup of the LED diode bridge.

Before with the single diode I was able to tune in stations from 10 to 15 miles away.  I was able to find the same stations again, so it is not worse, and I also found three more stations, the tower of one of these is just over 20 miles away!  Below is a map of the station locations I tuned in using this setup (click for a larger image).

So there seems to be some improvement.  I searched for mention of this online and in forums I read that using a full wave rectifier in an unamplified radio wouldn't help because of the voltage loss from the signal going through two diodes instead of just one (these types of radios work with very low power so any loss is bad).  However, my results suggest is does help.  For much beyond 20 miles I am going to run out of island.  I need to bring in signals from over 50 miles away to reach the next island, Moloka'i.  Perhaps next I will try to increase the size of the antenna.

Fox-Hole Radio

We built a foxhole radio as another weekend project a few weekends ago. 

First we strung an antenna (22 AWG) out the window to a tree in the backyard. 

Then I set up a ground wire using an outlet and a child safety plug to cover it (and a lecture to the kids about the danger of doing this wrong and exactly what I was doing and why).

(DISCLAIMER - Do not do this at home if you are reading this.  There are safer ways to set up a ground.  Stick a piece of metal into the dirt outside in the yard and connect the wire to that.)

Then we made some coils of wire over cardboard tubes and sandpapered off the enamel coating to tune the frequencies, and hooked up a diode on the other side of the circuit (in parallel between the antenna and ground).  The diode only allows current to flow in one direction, which removes half of the wave from the AM signal and allows the signal to be played in a speaker as sound waves.  The sound output for the speaker is between the diode and ground in the circuit.  The circuit has a resonant frequency that is adjusted by the length of the connected coil to filter different stations based on frequency.  We experimented with several different diodes and coils.

In the picture you can see a zener diode and a green LED (light emitting diode) both of which worked fine when hooked up in the circuit.  The trick is making your own diode.  I tried a few treatments of razor blade surfaces to a graphite pencil point in the circuit.  One blade I rusted in salt water and air for a few days.  Another was heated with a candle, which put on a layer of black carbon on one side.  Another I heated directly on an electric stove eye until it oxidized to a deep blue color.  The third one worked the best and is shown hooked up (with thumb tacks and cork board, no soldering here).  The pencil is held up and connected to the rest of the circuit by a bent safety pin.  The contact point of the graphite to the oxidized metal surface can be adjusted until a good diode contact point is found where the electricity only moves across in one direction.  We also tried a few different tunable coils with different lengths and wire sizes.  The one that worked the best was an intermediate size shown here (30 AWG).  The circuit is connected at different points along the coil to tune different radio stations.  It was very touchy a slight movement to the contact and the station was gone.  It worked better to add a capacitor to the antenna input side.

Above is the capacitor.  The antenna is connected to a square of aluminum foil placed in a book.  This is separated by a single page from another square of foil that goes into the circuit.  The radio can be fine tuned by placing different weights on the book, which changes the distance between the foil sheets. 

Here is the setup connected to our amplifier and plastic plate speaker.  We also plugged it into the microphone input on a laptop to monitor and record the signal with audacity.   Using an empty frequency, we were able to detect our home built motor running on another table by recording, noise removal and amplification.  The brush contacts in the motor acted as weak spark gap transmitter.  We were also able to get several local AM stations tuned in.  I identified three of them by the call signs and looked up their antenna locations online; they were 10 to 15 miles away.