Firstly Radio VNG was Australia's official time and signal service. Sadly, it no longer exists having been overtaken by GPS time technology. It was maintained by Australia's National Standards Commission and provided highly accurate and stable reference signals on 2.5, 5, 8.638, 12.984 and 16 Mhz.
This topic of a Radio VNG 5 Mhz Receiver will demonstrate many of the principles in the tutorials presented on this site including active antennas, impedance, resonance, toroids, impedance matching, band pass filters, low pass filters, oscillators, receivers and digital basics. Links to the appropriate electronic tutorial will be provided.
If you have access to a quality short wave receiver check out those stable reference signals on 2.5, 5, 8.638, 12.984 and 16 Mhz and PLEASE do send me a signal report from your area. BTW do not confuse the 5 Mhz with the strong WWV signal in the USA. This project can be modified for the reception of the other VNG frequencies.
I was an old time financial contributor to the VNG Users Consortium back in the days when it looked like the service would be abandoned in the name of the "holy grail" of economic rationalism. Thankfully, solely due to the co-operative efforts of so many great and wonderful people, it was able to be retained and then ultimately taken over by Australia's National Standards Commission.
This particular radio receiver will be fixed tuned to 5 Mhz to pick up the always accurate time-of-day (within one milli-second) encoded information which is part of the VNG 1 Khz modulation tone. This will then be used to build an always accurate digital clock display.
Radio VNG transmits time-of-day and day-of-year information as a modulated tone in the form of BCD (binary coded decimal) format throughout the 21st to 35th second inclusive after the synchronizing 200 mS pulse at the beginning of the 20th second past the minute. A 200 mS (milli-second) burst of 1 Khz (1,000 Hz) equals a binary one while a 100 mS burst of 1 Khz equals a binary zero. The full VNG time code format can be viewed here in figure 1 below.
Figure 1. - VNG time code format
If you don't understand the in's and out's of the BCD format and the concept of binary one's and zero's then go to digital basics for a better grasp of that topic.
In figure 2 below is a block diagram of our Radio VNG 5 Mhz Receiver. We will then discuss each section individually. Incidentally I will actually be constructing this project in the real world but, I'm electing to build the Radio VNG 5 Mhz Receiver "UGLY" style. That means "point-to-point" wiring on a piece of printed circuit board (PCB) rather than a dedicated PCB. WHY?, cost! I no longer have neither the facilities nor the inclination to etch a one off PCB myself. I can put one through a drawing program and have it made. The cost of that alone would exceed the cost of everything else in the project put together.
Figure 2. - Radio VNG 5 Mhz Receiver block diagram
I thought I rather elegantly covered the topic of active antennas on my old site some time ago. Naturally that is an incredibly biased opinion. On the same site I provided a suggested a somewhat near example for the radio telescope project. We will be duplicating that one here, heh!, heh!. I'm a big believer in re-cycling anything from rubbish to projects to gif files. Some modifications will be needed of course.
Figure 3. - Original amplifier to be used as an active antenna for Radio VNG 5 Mhz Receiver
Because I'm going to connect to a short telescoping antenna I need to amend the input circuit. The output circuit just needs to be modified for connection to the Radio VNG 5 Mhz Receiver which in actual fact is a 16 pin Philips TDA1072A AM receiver integrated circuit or AM radio on a "chip". I suggest you review some of my comments about this amplifier and associated filters in the radio telescope project page.
Figure 4. - Revised active antenna for Radio VNG 5 Mhz Receiver
More next week or whenever.......
am radio receivers
radio receiver basics
tuned radio frequency TRF receivers
regenerative radio receivers
fm radio receivers
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Updated 16th March, 2001