Welcome to the Lord Howe Island Non Directional Beacon (NDB) Page. Although pretty pointless, I do take an interest in aviation and navigation aids, and I took a few pictures of the Non Directional Beacon at Lord Howe Island, Australia, which one can get very close to owing to the absence of a boundary fence! You can see the NDB on the photo above - its two masts can be seen just left of centre.

Firstly, what a Non Directional Beacon actually is. A non directional beacon is a simple radio transmitter operating slightly below the AM broadcast band, or in the Longwave band. It sends out a continuous signal, a "carrier," which is often modulated with the station's identification, in Morse code. In this case, the identification is LHI, or dit-dah-dit-dit dit-dit-dit-dit dit-dit ( .-.. .... .. ). This code helps the pilots confirm that they are tuned to the right frequency. The pilots have on their flightdeck an instrument called the ADF or Automatic Direction Finder, which simply consists of a needle which points toward the NDB. Thus, the pilots can locate and track towards one. This is very useful for a place such as Lord Howe, which, during inclement weather, can often be very hard to visually pinpoint. The effective range for this NDB is 140 nautical miles (nm) during the day, and 110nm during the night.

As with most navigation aids, there is a small building housing the transmitters (there are often two of them - a primary and secondary, just in case one fails) next to the antenna array. Here is a photo of LHI's one:

Here you can see that the building also doubles as a water catchment facility, which no doubt is utilised during droughts. Behind the building, you can see the battery store. These are kept continually charged, and can power the NDB transmitters for a significant amount of time in the event of a power failure. Here is a closer view of the battery store:

Before the signals that are sent out by the transmitter can reach the antenna array, they must be tuned and filtered so as to avoid emitting unwanted signals, and also to optimise the output for the antenna. Here is a wide view of the Antenna Tuning and Coupling Unit, the device which does all this.

Here is another shot, this time closer up. Note the RF (Radio Frequency) hazard sign. If I develop a tumour at an early age, I guess I'll know why.

From the tuning unit, the refined signal passes up the feedwire (via the feedline) to the main antenna array, which resembles a clothes line. Here is a shot of the junction.

Here is a shot of the whole antenna array (note: it was a very dark day when I shot this, and, combined with poor scanning, this image is very dark. I will fix it soon.).

And finally, located about 2 kilometres south of the NDB station, there is the Distance Measuring Equipment (DME) station. This is a system whereby the aircraft's DME equipment sends out pulses on the station's frequency (in this case, a little above 1 GHz). When the DME station receives this 'pulse', it sends out one in reply to the aircraft. The elapsed time from send to receive is measured and thus the distance out is computed (using the known speed of light/radio waves). The speed towards the station is also recorded. LHI's station sits just to the south-east of the runway 10 threshold, and has a morse code identification of LHI (dit-dah-dit-dit dit-dit-dit-dit dit-dit)