Amplifier Circuit Diagrams

Kalundborg 10 Mhz Frequency Reference Schematic Circuit Diagram

Utilizing Kalundborg’s Carrier in Frequency Standard:

Since the long-wave broadcast station Kalundborg adjusted its frequency from 245 kHz to 243 kHz in adherence to the CCIR’s recommendations for a 9 kHz raster in the LW and MW bands, it has opened up the possibility of utilizing the carrier in the locked frequency standard outlined in Ref. 1. Kalundborg, a 300 kW long-wave transmitter in Denmark with a range of about 500 km (300 miles), makes this article particularly relevant for our Scandinavian readers.

Frequency Reference Adjustment for Kalundborg:

The proposal in this and the subsequent item (‘Preamplifier for Kalundborg Frequency Reference’) involves modifying the divider in the frequency reference to accommodate a carrier input frequency of 243 kHz instead of the original design’s 77.5 kHz (the transmit frequency of DCF77 in Germany). The alterations are depicted in the simplified block diagram, Fig. 1, which should be compared with Fig. 1 in Ref.1 for clarity. In practical terms, the original circuit of the reference undergoes changes significant enough to necessitate a new circuit diagram, as illustrated in Fig. 3. The new circuit proves much simpler than the original, mainly due to the omission of certain sections, including the VLF preamplifier (T1–T4 in the original design), the 10 MHz ‘locked only’ output (IC7 and T12 in the original design), and the ‘error’ detector (N2, N3, N4, and the beeper in the original design).

Kalunndborg 10 Mhz frequency reference Schematic diagram

Kalundborg Circuit Overview:

In the ‘Kalundborg’ circuit illustrated here, the 10-MHz signal from X1 and T3 undergoes multiplication by 3 through the parallel-tuned circuit L4-C39. The resulting 30-MHz signal is then subjected to two successive divisions—first by 100 (IC5) and then by 100 again (IC6). These divisions yield the 3 kHz reference required for the multiplier IC3. Simultaneously, a 240 kHz signal, crucial for heterodyning with the 243 kHz carrier, is derived by dividing the 30 MHz signal by 25 (IC5) and subsequently by 5 (74LS90).

Antenna and Tuning Mechanism:

The antenna, formed by an inductor wound around a ferrite rod and resonated by capacitors C1, C2, and C3, connects directly to the balanced inputs of the SO42P mixer (IC1). The error signal at the multiplier’s output (IC3) undergoes filtration and transformation into a tuning voltage, directed to a dual varicap, D5. This varicap has the capability to detune, albeit to a minor extent, the 10 MHz quartz oscillator, effectively closing the phase-locked loop (PLL). When Kalundborg is received with sufficient strength (accomplished by rotating the ferrite rod), the LED at the output of IC8 illuminates, providing a ‘rock-steady 10 MHz reference signal at the output of N2.’

 

Kalunndborg 10 Mhz frequency reference Schematic diagram

Figure 2 shows a detailed diagram of the x3 multiplier. Inductor L4 consists of 4.5 turns of 0.5 mm dia. enameled copper wire on a ferrite core. The former has an outside diameter of 6 mm, and L4 is drawn out to a length of about 8 mm. The operation of the multiplier is easily checked with the aid of an oscilloscope and a frequency meter, with the signal levels being quite high. The core in L4 is adjusted for the highest 30 MHz level at pin 5 of N4.

Kalunndborg 10 Mhz frequency reference Schematic diagram

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