Monday, November 15, 2010

A 6-Inch Tunable Loopstick

The homemade tunable loopstick device, similar to the Q-Stick by DXTools continues to be a popular article on RADIO-TIMETRAVELLER. Let's revisit this simple device and build another one, this time a 6-inch version.

Old transistor or table radios can be had for almost nothing at your local yard sale or flea market. I have reported on yard sales and flea markets before. Great radio values can be had from uninformed sellers.

Don't Laugh at Yard Sales
Another Deal, The Panasonic RF-565
Viva Flea Markets

I always keep my eye out for both working and non-working varieties, as the non-working ones can be stripped for their parts. Most important for building a tuning device: the variable capacitor and the ferrite loopstick.

The better buys are the radios having longer loopsticks or serviceable tuning capacitors. Many pocket radios are configured with the tuning knob directly connected to the capacitor, though the capacitor itself is often small in this case. Larger radio varieties often have a slide rule type dial mechanism, usually driving a more substantial capacitor. Surprisingly, most tuning capacitors in old radios, even the small ones, have 1/4 inch shafts, though short. So if the main tuning knob is intact and is one which is connected directly to the capacitor shaft, all the better. Save the knob.

This summer's flea market take was four old transistor radios. One was pocket sized, and the others were the type you would set on a desk, about the size of a small book. Three of the four had seen better days and did not even work. The other actually worked decently enough to keep and experiment with. Each cost two dollars or less.

The best loopstick of the bunch was a nice six inch one, a rod instead of a bar, wound very nicely with evenly-spaced turns of Litz wire to about 80 percent the full length of the stick. A short IF coil was at one end. I carefully removed the IF coil, as it is not needed.

I selected a small tuning capacitor which had a nice dial knob. At the end of the loopstick where there was room, I taped the capacitor to it by slotting the tape with a razor so it would fit over the shaft. The capacitor could also be hot glued to the rod if desired.

The coil wires were then carefully soldered to the center and edge terminals of the capacitor, forming the parallel tuned circuit. Be sure to use the edge terminal having the greatest capacitance, as the other one is the IF side of the capacitor with lesser capacitance. If you want to get fancy, you could enclose the loopstick device in a short length of PVC pipe, capping the coil end, and fastening the tuning capacitor on the other end of the pipe.

To use the loopstick, simply hold it parallel and near to the internal loop in your radio, then tune it to peak the signal your radio is tuned to. Rotate the two together, radio and loopstick, for maximum signal. The loopstick can also be rotated independently to null an offending co-channel station. A short length of wire or even a longwire could also be attached to one of the capacitor terminals, providing more signal, though it will lessen the directivity of the loopstick.

Sunday, November 7, 2010

KDKA Turns 90 Years Old

In 1920, Dr. Frank Conrad was an engineer in the employ of the Westinghouse Electric Company. He was also an amateur radio operator. With the release by Congress in July 1919 of all privately held radio and telephone equipment now that World War I had ended, the race to commercialize the new science of radio telephony was on.

To test transmissions during the war, Conrad placed one transmitter and receiver at the Westinghouse plant and another above his garage at home, four miles away. When the war ended and the government lifted the restrictions on amateur radio telephony, Conrad went back to his experimentation from home.

After the war, a fierce battle ensued between the US government and the Department of the Navy over control of the airwaves. The government won out and settled on the Department of Commerce to run things, wresting control from the Navy's hands. After the dust cleared, in April 1920, Conrad applied to the Department of Commerce to license his station. He was given the call letters 8XK.

Westinghouse saw that Conrad's experiments might be important and potentially profitable, and so with Conrad's help, started construction of a new transmitting facility on the roof of the Westinghouse plant in East Pittsburgh, PA. A presidential election campaign was in full progress that year, the election of 1920. The Republican ticket, comprised of Senator Warren G. Harding of Ohio and Governor Calvin Coolidge of Massachusetts was paired against the Democratic ticket's Governor James Cox of Ohio and former under secretary of the navy Franklin Delano Roosevelt.

On October 27, 1920, Westinghouse's radio facility was completed, and the Department of Commerce granted it the historic call sign KDKA. It transmitted on a frequency of 833 KHz (360 meters) with a power of 100 watts. Only two frequencies were assigned for broadcasting at this time. The other was 619 KHz (485 meters).

Hastily constructed, the "radio facility" was hardly more than a simple metal shack with all the necessary wires and equipment, and a desk from which an announcer could report election results. The election was slated for November 2.

On Tuesday, November 2, 1920, election night, up in that metal shack four men in dark suits compiled election returns received via wired-telephone from the newsroom at the Pittsburgh Post. The results were handed to one Leo H. Rosenburg. Leaning forward into an early microphone, Rosenburg's voice was sent through wires and apparatus out into the ether. It is estimated that between 500 and 1000 listeners heard this broadcast.

The excitement triggered by KDKA's 1920 election coverage set off a national hysteria for radio. Within weeks, Conrad had upped KDKA's power to 500 watts. It was now being heard as far away as Washington, D.C. Conrad started adding entertainment programs according to a schedule. Radio broadcasting, as we know it, was born.

Happy birthday KDKA-1020, Pittsburgh, PA, now 50,000 watts!

The Aeriola Senior regenerative radio.
Introduced December, 1921. $65.00