Eighty years ago this month, the May 1937 issue of All Wave Radio magazine carried a description by J.F. Gordon, W7CNP, of his method of sending facsimile by radio. The received image is shown above. While the system was quite simple in theory, it does appear to be quite labor intensive.

The received image, shown above, is reproduced on photographic film. The original transmitted image, drawn in pencil, is shown at the left. Since the entire image is drawn in pencil, it is conductive, and can be scanned by a conductive stylus. There needs to be continuity between all points on the image, and for this reason, the letters are all linked by a pencil line. Before transmission, these lines are covered up with coil dope or another insulating substance.

The image is then scanned on a normal phonograph turntable, powered by a synchronous motor to keep the speed at both ends of the circuit exactly the same. The image is scanned by a stylus riding on a threaded rod geared to the turntable motor.

An audio signal is sent through the circuit from the pencil lead to the stylus, and this signal is used to modulate the transmitter.

At the receiving side, an identical turntable is employed. For receiving, the stylus is replaced by a neon lamp. A piece of photographic film is placed on the turntable, which of course needs to be in a darkened enclosure. A second neon lamp is placed outside the box to make sure the system is receiving properly.

The neon lamp is driven by the receiver audio. Assuming everything is working properly, when the film is developed, it sould reveal a negative image of the original pencil disk.

The mariner shown here 60 years ago on the cover of the May 1957 issue of Popular Electronics is demonstrating two methods of radio navigation described in the magazine, using a National NC-66 receiver and its optional external loop antenna.

Using the receiver alone, she is using the method that required no special direction finding antenna, and that provided accurate results even in a small bouncing boat.

That method used the “A-N” longwave radio ranges which were still operating between 200-400 kHz. While these aeronautical radio ranges were most often used by pilots, there was no reason why they couldn’t be used by boaters, as long as the craft had a longwave receiver aboard.

As we described in an earlier post, each of these beacons transmitted two signals in a four-leaf clover pattern. In two quadrants, the Morse letter A (dot-dash) could be heard. In the other two quadrants, the letter N (dash-dot) could be heard. At the intersections of the two signals (“on the beam” normally followed by pilots), the signals would merge and be continuous.

For example, a boater shown at the position marked 1 near the bottom of this map would first tune to 227 kHz to beacon HEM at Mitchell Field, Long Island. She would hear the A. Then, she would tune to 248 to listen to the beacon IDL at Idlewild and hear the N. Finally, she could tune in EWR Newark on 341 kHz, where N would be heard.

By consulting the chart and using the process of elimination, this would narrow her location down to the relatively small quadrangle off the New Jersey coast.

The magazine also described the next logical step in navigation skill as use of the optional loop antenna and null meter shown at the top of the picture.  As we’ve described previously, such an antenna would allow an exact bearing to any station, using either a marine beacon or standard AM broadcast station.

Eighty years ago this month, the April 1937 issue of Popular Mechanics carried the plans for this simple 40 meter transmitter employing a single 6L6 tube. The set used an 80 meter crystal, and according to the article, using the crystal on its second harmonic resulted in particularly good keying.

The set called for a power supply delivering 400 volts at about 100 milliamps.

It was said to have a range of about 500 miles.

Shown here on the cover of the April 1937 issue of Radio News is E.M. Walker, W2MW, at the mike of his 5 meter transmitter, the construction details of which are found in the magazine. The set was billed as ideal for the ham who couldn’t afford a crystal controlled rig for the super highs, since he reported many reports of the signal being comparable to crystal control. The transmitter itself for CW consisted of two 6L6 tubes. The accompanying modulator used four tubes, two push-pull 6L6’s along with a 6F6 and 6CF serving as audio preamplifiers.

The transmitter was very compact, with the RF portion and modulator each mounted in 14x7x8 cabinets.

The author stressed the importance of care in winding the oscillator coils, and noted that some experimentation might be necessary to get them right on frequency.

Schematics of RF section (left) and modulator (right).

Prior to World War II, the relatively new FM broadcast band was located at 42-49 MHz. After the war, it moved to its current home at 88-108 MHz. This false start was one of the reasons why FM took years to catch on: The early adopters owned receivers which were now useless, since the stations had all moved.

One solution was building a converter, and a number of designs were available. One of the simplest is shown here, and appeared in the April 1947 issue of Popular Mechanics.

The circuit originated with Henry R. Kaiser, the chief engineer of FM station WMOT in Pittsburgh. When WMOT changed frequencies, there were about 6000 obsolete receivers in the area which could no longer hear the station.

Kaiser originally designed a circuit with a crystal oscillator, and a 1N34 diode as mixer. During experiments, the tube oscillator failed. Much to his surprise, the circuit converted the frequency of another FM station. With a bit of tweaking, he came up with this circuit which put his station on the old receiver’s dial without any power.

The article doesn’t explain how the circuit works, probably because the author didn’t know. But at least for a strong signal, the circuit did work, and could be used to put some of those obsolete sets back in service.