Oma-2500 Time Standard Receiver

OMA-2500 is a 1 kW time standard trans- mitter on 2500 kHz. The station is located in Liblice, Czechoslovakia, and is operated by the Astronomical Insti- tute of the Chechoslovak Academy of Sciences. Contrary to time standard transmitters in the VLF band (DCF77, HBF), modulation is pure AM instead of a combination of AM and PSK or FSK. This means that the seconds pips transmitted by OMA-2500 are free from phase noise, which is a must for some types of PLL, particularly in communications equipment, where the 2500 kHz signal supplied by a time standard receiver is used for generating or deriving other frequencies of equal stability. Transistor Ti is configured as a regenerative buffer which acts as an ac- tive filter with an effective Q (quality) factor of about 1,000 at a 3 dB bandwidth of 2.5 kHz. The received signal is further raised in amplifier T2-T2 before it is ap- plied to active crystal filter T4-4C1 which ensures a 3 dB bandwidth 9f about 500 Hz. Output amplitude of the re...