Hamakuapoko Radio Beacon, Technical Information

The triangular loop antennas had a 300 ft. base and were 72 ft. high. Their orientation and method of coupling to the transmitter produced equal signals from each loop at a bearing of 54 degrees from North.

The output from the transmitter was switched between the two loops by a relay which was activated by the keyer.



As shown in the graph above, a series of N's in Morse Code (dash-dot's) connected the transmitter to the N-S loop. Likewise, a series of A's (dot-dash's) connected the transmitter to

the E-W loop. Note that when either loop was activated, the other was not. When the aircraft was where the signal strength from the two antennas were equal, the A's and N's merged to form a continous signal. The dashes and dots were formed by a switch activated by a motor-driven cam.

The transmitter was an obsolete 5-Kw spark type converted to vacuum tubes (pair of UV-851's). The tubes received their 500 Hz ac plate voltage via opposite legs of a center-tapped transformer. When one tube was operational the other tube was inactive (vacuum tubes operate only with a positve plate voltage). The result was that the 290 KHz radio frequency was produced on each half cycle of the 500 Hz plate supply. The transmitter output can be described as a 290 KHz carrier amplitude modulated with a predominately 1000 Hz tone.

The Signal Corps PE-40 was a 5 Kw dc generator powered by a water-cooled, 4 cylinder gasoline engine. It powered the transmitter tube filaments, 500 Hz generator, keyer motor, antenna switching relay as well as the shack lighting.

References

Beacon Background Information

Beacon Chronology