Beacon


Configuration

Beacon contain five parts: power suply, temperature control unit, identifying keyer, transmitter and antenna.



Power suply

Network voltage is transformed to value 15 V. After 4-way rectifier folow integrated stabilizator MA 7812. Three DC voltage are on the output of power suply: 15 V nonstabilized for heating of temperature control unit, 12 V stabilized for transmitter and for control circuits of temperature control unit and 5 V (voltage is eliminated from 12 V over the resistor) for identifying keyer. Whole power suply is fused on primary and secondary side.



Temperature control unit

Heating part and transmitter are in the one block. This one is located in metal box, which is heat isolated. Temperature sensor is termistor and heating body is power transistor. Electronic part contain integrated circuit MAA 723. Control unit working in proportional mode. Power input of heating is 6 W. Temperature is maintain on 50 degrees Celsius inside.



Identifying keyer

Whole keyer contain folowed integrated circuits series TTL: MH 74154, MH 74150, two pieces of MH 7493 and timer NE 555. Identification is "stored" in diode matrix, which has 16 multiple 16 swiched points. NE 555 generate stroke frequency and that going to two counters MH 7493. These counters control circuits MH 74154 and MH 74150 (multiplexer and demultiplexer) - they read diode matrix. Speed of transmitting text is depend of frequency stroke generator. Text of beacon is: "OK0EN BEACON QRP" and after this folow dash 8.5 second long. Whole text, including dash, is repeating every 29 seconds. It represent speed 50 characters per minute.



Transmitter

It is modificated circuit by OK1CZ. Oscilator is on transistor KC 508. In series with crystal 3600 kHz is connected varicap for fine tuning frequency of transmitter (about +/- 150 Hz). After oscilator folow power amplifier (KFY 34) and from its output go carrier over the double PI cell and serial inductor to the antenna. Keying is done in the collector of PA tranzistor by other transistor KF 517. Keying pulses are not going to its gate directly, but by small relais, because of right form of CW signals without sharp edges. Power input of PA is 300 mW. When we will supposed efficiency 50 %, it is possible to say that power output is 150 mW.



Antenna

Antenna is a half wave dipol. Shoulders contain angle 100 degrees and are little bit inverted - about 5 degrees. Direction of maximum gain is oriented to east - west. Beacon is located in loft of private house. One of shoulders of antenna is in loft (because piece of land is not large) and second is cathed between top of the roof and the ground. Antenna is only 8 metres above the ground with the good conductivity (large pond is near).



General configuration

Transmitter and heating part of temperature control unit with heat isolation is composed in the one mechanical block. Other parts of beacon (without power suply), are installed in the next plastic box. This one is connected to the transmitter with cable. Both two parts are located in the big heat isolation box (second isolation). Power suply is separated in the metal box, out of beacon. Whole equipment is protected against fire. Power input of whole beacon from network 220 V is 10 VA.



Thanks

Thanks to OK1CZ, OK1MC (silent key), OK1DGI, OK1FAQ, OK1FIP, OK1FVD and OK2PXJ for advises and help with construct of beacon. For publicity of beacon in OK and foreign countries thanks to OK1HH, OK1RR, OK1CRA, OK1FVD, OK1FWA, OK2PXJ, DJ5QK, DL1AAA and G8PG.