Listening to UK Long Wave Non Directional Beacons (NDBs)
Created 29.12.06

INTRODUCTION

With the RSGB discussing a possible experimental amateur allocation at the top end of long wave near 500kHz I took an opportunity during the Christmas break to take a listen to the LW band between 275 - 500kHz. I was curious to hear what’s still there these days. A week earlier I’d built a small VLF up-converter to listen out for SAQ on 17.2kHz and by increasing the cut-off frequency of the input filter I managed to bring up the sensitivity some 20-30dB in the LW band, so there was plenty of scope for LW reception with my 50 foot wire down the garden using the converter with the FT817.

LW SENSITIVITY

You may find that a preamp is needed on your own receiver if it covers long wave, as amateur rigs and general coverage receivers are often deaf in this part of the spectrum. Although broadcasters use many kilowatts the beacon signals are designed for relatively local reception only on approaches to airfields, so can be considerably weaker.

As a guide to sensitivity on LW (for those in the UK) there is a useful Greek data transmitter on about 138kHz that sends a carrier and, every few seconds, a burst of data. If you can hear this as S9+ you have a reasonably sensitive set-up. If this is weak then you need to try harder with your set-up.

FEWER BEACONS

A lot of the LW marine beacons that used to be there seem to have disappeared since I last looked some years ago. In the age of sub £100 GPS receivers with accuracies of a few metres the sailors around the UK and Northern Europe have no need to direction-find using a couple of MCW beacons: the GPS receiver just tells them.  The MCW and CW beacons that remain appear to be linked to airfields. I also noticed several other types of long wave beacon sending data but I did not try to decode these.  I believe they now send differential GPS data to improve GPS accuracy. Without decoding the data it was not possible to identify these.

FINDING THE BEACONS

My search started by listening for a local beacon about 10 miles down the road at Cambridge Airport. This has been around for years putting out a few watts to a Marconi antenna up near the end of the runway. Sure enough it was there nice and strong on 332.5kHz sending the letters “CAM” in slow CW. A casual tune around and I had another half dozen such beacons in the log.   All were sending their callsigns in very slow modulated CW so even if your morse is not very good you should be able to quickly copy them after a few repeats.

A search for “LW NDB” on Google brought up an excellent site about beacons of all sorts http://www.beaconworld.org.uk/enter.htm. In amongst lots of useful data on this site was a full list of operational long wave beacons around the UK. Using this list as a guide (and with a cup of tea in hand!) I slowly tuned for about 45 minutes from the LF to HF end of the beacon band to see what could be identified. Many beacons were copied with the FT817 in AM mode but for some I put it into CW mode and turned on the narrow 500Hz filter. The list below shows what could be copied without too much effort in daylight on that mid-winter day. At night I expect many more would be audible. The last time I listened in this part of the spectrum many years ago it was possible to hear LW beacons from as far south as Spain and up to Norway without any real effort at night.

Among the stations identified were a few that did not appear on the UK beacons list. These may be new ones or perhaps are located outside of the UK. I am sure that, with a little patience, all of the NDBs in the UK could be copied, especially with the aid of a directional loop antenna to null out some stronger stations and allow copy of weaker ones, especially at night. 

Some listeners make an entire hobby out of beacon reception. Many beacons send QSLs in response to helpful reports (not sure about UK NDBs though) and certainly amateur HF beacon operators always appreciate such reports. 

LOG OF NDB STATIONS RECEIVED (mid-winter daylight, near Cambridge UK)

 CONCLUSIONS

Based on the results during my brief listen to this part of the spectrum I could imagine good inter-G coverage with relatively low power even with the inefficient antennas that we could erect in our back gardens on long wave. It should be somewhat easier to get useful results around 500kHz, if it ever happens, than on 136kHz.

So, have a tune around the long wave beacons sometime to see what you too can hear.