LF Non Directional Beacon (NDB)These
pages contain photos of two NDB installation, a fairly typical unit for a small airport/airfield, and another as installed upon a ship. This latter unit must surely have the smallest antenna of any NDB installation.
This NDB is currently installed and is operational at Blackbushe Airport, approximately 30 miles west ot London.
The unit runs 8 watts output on 328kHz to a electrically short vertical with centre loading and a capacity hat. The signal is an amplitude modulated (AM) by a 400Hz tone keyed with the callsign BLK.
The aerial current is approximately 0.25A which yields a field strength of 20uV/m as measured by NATS, the UK's National Air Traffic Service monitoring station at Pailton near Rugby, a distance of about 120km from Blackbushe. Although the beacon is only licensed by the Civil Aviation Authority for navigation purposes up to 15 miles from the airport, it can be heard on the French Channel coast, and reception reports from Spain and Italy are received by the Airport from time to time.
The NDB installation. The antenna to the left which looks a white tube mounted on a tripod is for the DME (Distance Measuring Equipment) a type of Secondary Radar.
The Transmitter - a Southern Avionics SS250CV Unit. The SS250CV can run upto 25 watts.
The Transmitter open.
The Aerial Tuning Unit (ATU)
The ATU with door open
Inside the ATU
Another view of the ATU showing the Variometer.
Download the ATU Auto-tune circuit diagrams in 
(550kb)
The DME - by Fernau Avionics Ltd.
This NDB was installed upon the drillship "Pelerin". Drillships frequently have NDBs as part of the standard "kit" to assist the approach of helicopters.
The NDB electronics are housed on the platform half way up the mast - the platform was about 8ft above the deck. The antenna seems to comprise of no more than a loading coil and a large capacity hat.
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Last update 15/5/2001