The UK 500kHz Experiment


The 500kHz part of the frequency spectrum has for many years been used by the maritime services. In particular the 500kHz spot frequency was an international calling and distress frequency monitored 24 hours by most nations. With the decline in the use of morse code on board ships and the move in recent years to satellite communication it is no longer used for that purpose in most countries and most ships no longer have equipment for the band. See Wikipedia for an interesting history.

In recent years various countries have looked into obtaining an amateur allocation at 500kHz. It forms a convenient bridge between 136kHz (becoming available in a lot of countries) and the 160m Top Band amateur allocation. The RSGB was a leading proponent and presented a paper at the IARU Region 1 Conference at San Marino in 2002 suggesting a 10kHz slot between 470-490kHz. This was supported by Belgium, Holland, the USA and New Zealand. A working group was established.

There is a separate proposal by the Marine Radio officers to make 500kHz an 'International Heritage site'. In November 2006 two special stations GB500KCS and DL500KHZ were active on the normal amateur bands to recognise this proposal.

In January 2005 two amateurs in Germany obtained special permits, DI2BO and DI2AG for experimental transmissions on 440kHz. They subsequently obtained a second licence for operation on 505.1kHz. In December 2006 the Swedish station SM6BHZ obtained permission to transmit on 505.0-505.2kHz with 20W erp.

On September 15th 2006 the FCC in the USA granted a Part 5 experimental licence to the ARRL for a number of stations to operate for 2 years with the callsign WD2XSH between 505 and 510kHz. You can find more about this experiment at

In March 2007 Ofcom announced that UK amateurs were able to apply for special experimental NOVs to operate for one year between 501 and 504KHz with 100mW erp. The UK is the first country in the world to make 500kHz licences generally available to its amateurs. These NOVs were subsequently renewed and continued until 2012.

At WRC-2012 a proposal for an allocation around this frequency was tabled and after much discussion it was approved that 472kHz-479kHz would be available to the amateur service on a secondary basis from 2013. NOVs for the new allocation became available in the UK from January 2013 and the 500kHz NOVs were cancelled.

G3YMC has no plans at present to become active on the new band but continues to maintain an interest. These pages will be kept as a record of the time I was active on 500kHz.

The UK 500kHz NOV

The UK Amateur Radio Special Research Permit allows operation in the band 501-504kHz . It is available on application to UK Advanced Licence holders and was initially valid for one year until 29th February 2008 and with a maximum poer of 100mW erp. It was subsequently extended to run until 28th February 2009 and the power limit was increased to 1W erp. The application form is the same one used by amateurs who wish to use high power equipment on other bands for such things as moonbounce. As such the applicant has to estimate field stengths at the boundaries of his property for safety and interference considerations. Of course with 1W maximum erp field strengths will be comfortably within limits, but there is concern of interference to consumer electronics, particularly MW and LW reception, so detailed layouts of the property and proposed antennas have to be supplied. I drew up a scale drawing of my house and garden, showing neighbouring properties and the vertical aerial, a photo and extra notes on a separate sheet. It seemed to work as I received my NOV promptly. Ofcom do seem very concerned of the potential for interference but to date there have been no reported problems of this nature.

500kHz at G3YMC

Soon after the UK NOV was announced I had a listen on the band. My Datong U/C1 was quickly connected to my untuned longwire and fed to my Elecraft K2. I heard several G stations at once, although at this time signals were a bit on the weak side as was the band noise. But it was sufficient to inspire interest so I went about applying for an NOV.

500kHz transmitter

While waiting for this to arrive I though of the best way of getting on the band from my very limited QTH. The Butternut vertical which I had been using on 160m during the winter seemed to be suitable, and a quick analysis with Reg G4FGQ's vertload program showed that base loaded it could be expected to give an efficiency of around 1%, enough to give the 100mW maximum erp with around 10W drive. From my 136kHz days I had a 1mH variometer coil donated to me by Steve GW4ALG. Would this do the trick? It was quickly brought out of storage and put in my old dustbin, which was moved to the base of the vertical and connected up. The band was now found to be far more lively, with quite a few 599 stations to be heard. It looked as if I was in business!

On to ideas for the transmitter. I had previously designed a simple VXO rig for the UK 5MHz allocation. I decided to use this as a basis, using a pair of suitable crystals spaced at 500kHz. Using components largely available from my junk box I soon got a little transmitter knocked up and was almost ready to get on the air. By this time my NOV had arrived. See here for the design I ended up with.

My receiver is my Elecraft K2 driven from a Datong U/C1 Upconverter on 28MHz. I have previously used it on 5MHz - see how to configure it here. Several of the 500kHz operators also use the U/C1, it works well with no evidence of overload from broadcast stations although its 116MHz conversion oscillator does drift a little.

Follow the links for more information about my station and experiences on the band.