The secret listeners of world war 2

Amateur radio prior to 1939

The majority of amateur radio transmissions were in morse code with stations sending greeting messages just as we do today. Much of the equipment used was home build but some amateurs did have commercial equipment in their shacks.

Outbreak of war

In 1939 many countries suspended all amateur radio licences, in effect preventing all radio amateurs from using their transmitters. In the UK this suspension lasted until 1946.

With many radio amateurs at a loose end, MI5 established a unit known as the Radio Security Service (RSS). The aim of this new service was to harness the skills of radio amateurs to detect and monitor enemy radio transmissions.

In the UK around 1500 radio amateurs were recruited by MI5 through the Radio Society of Great Britain (RSGB). As radio amateurs they would have been an ideal choice, being able to read Morse code under difficult conditions, being able to operate & maintain shortwave equipment.

The volunteer interceptor

Radio amateurs found themselves being asked to sign the official secrets act prior to being enrolled as a volunteer interceptor (VI).

These new volunteer interceptors were initially tasked to listen for enemy spies in the UK, agents in the low countries, and German radio traffic. The majority of the signals would have been in Morse code, in plain language and also Enigma coded Morse signals.

Initially, it was thought that amateur operators were perfectly situated to locate the radio transmissions of spies who might be active on British soil. They searched the bands for suspicious signals and sent the encrypted text they copied for analysis. Sworn to secrecy, the VI’s did not know what, if anything, they had accomplished until the secret was revealed in a 1979 BBC TV broadcast, “The Secret Listeners.” They had discovered the encrypted communications networks of the Abwehr, greatly enhancing WWII intelligence efforts.

Find out more

To find out more about the role radio amateurs played during world war II visit us at the National Radio Centre, Bletchley Park, where you can see the equipment used by the VI's. Alternatively visit Secret listeners.

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So you want to learn morse

by Keith Hotchkiss • 8 August 2020

This is possibly the most frequently asked question I get asked, by visitors when volunteering at the National Radio Centre. The short answer is yes, and it may surprise you to know how many. Within the hobby of amateur radio there are operators around the globe who daily tap away on the key, sending out those dits and dahs to other radio enthusiasts. Just tune to the lower portion of the bands and you will hear their transmissions. OK, but why use morse code? Possibly the second most common question visitors ask. The simple answer is because we can. For many amateurs they have grown up in the hobby using nothing but morse, so to them it's what they enjoy doing. For others it is just one of the many modes they choose to use in making contact with fellow radio hams. Certainly it is not everyone's thing but its use is still strong. One of the advantages of using morse over voice communication is that vast distances can be achieved using relatively low power in comparison to voice modes. Many morse operators tend to transmit using fairly low power (QRP) and have great success in contacting hams around the world. Morse, surprisingly can be received by radio hams when conditions are relatively poor. In these poor conditions the use of voice communication is virtually impossible. So how do I go about learning morse? I can only speak from my own experience. The first thing I would say is that you must really want to learn morse. It will take time, you will have periods when you just can't make progress but you need to persevere. Please don't expect to do this in an hour and be on the air chatting, that isn't going to happen. 1. Forget dots and dashes! That's right, stop looking at morse as dots or dashes, instead think of them as dits or dahs. Why? because that's what morse sounds like, a short dit and a longer dah. Where a dit is at the start or within a letter we use di (pronounced as de). 2. Separate the code down into blocks of five So start by looking at the first five letters of the alphabet, A to E. Write them down and put the corresponding morse code next to them, just like I have below: A: Di Dah B: Dah Di Di Dit C: Dah Di Dah Dit D: Dah Di Dit E: Dit Say them to yourself and start to pick up how each letter sounds. It is the sound that is important rather than the dits or dahs. Once you think you have a grasp of these five letters try putting them together in various combinations. Sure you are a bit limited but give it a go, just like this example: BAD: Dah Di Di Dit, Di Dah, Dah Di Dit Note that there is a small pause where the comma is between the letters. When you are happy to move on take the next fiver letters and do the same, only now combining them with the five you already know. Guess what if you do five letters each day in a week you will have the whole alphabet. Then its time to look at the numbers and these are fairly simple. OK, so how do I pick up morse for real? Great question and the answer is in whatever way you feel matches your learning style. Some people listen to tapes of morse others listen to morse on the air and some use one of the many morse code turors available as software. Whatever method you use try and listen to the morse characters at the right speed for you. When I say this I need to explain that you can send or receive a morse character at 12 words a minute but with an extended pause between each letter. This is known as the Koch method of learning morse. The benefit of learning morse this way is simply that as you become more proficient you can reduce the pause between letters until it flows naturally. I would suggest that when you listen to morse write down what you hear in an exercise book. Don't worry if at first you only get the odd letter, over time the number of letters you get will increase. But why the exercise book? It is a great way to look back at your progress from your first attempts to where you are know. I know when I first learnt morse in the mid 1980s I did this and it made me realise how far I had come in such a short time. Can you recommend software for learning morse? I sure can. The best freeware program currently is written and supported by Ray Burlingame-Goff (G4FON). This is an outstanding piece of software which will enable you to practice both sending and receiving five letters, as I have described. You can visit Rays website to download it at G4FON Please let me know how you get on and I hope to catch you on the key soon.

How to build a Multi-Mode Digital Voice Repeater

by Keith Hotchkiss • 7 August 2020

I did ask this question to myself several times during the build of GB7PP, but the reasons to build a Multi-Mode Digital Voice Mode Repeater (MMDVM) are numerous. The main reason, I believe is that the MMDVM repeater offers users the ability to access multiple digital modes (the clue is in the title). With an MMDVM repeater users can use D-Star, DMR, C4FM, P25 and NXDN all on one repeater. For builders wanting a bit more excitement they can also bridge between modes, offering even greater scope for use. So what do I need? The first thing you will need is a site or location for your proposed repeater. The coverage, ideally should compliment existing repeaters in your area to enhance coverage. The second thing you will need is a licence from your licencing authority. In the UK this is OFCOM and all applications are processed via the Radio Society of Great Britain (RSGB). Their dedicated vetting agents make the process fairly straight forward. While your application is in think about the equipment you are going to use. In this example I will describe the kit I used to build GB7PP. Other builders may choose to adopt other equipment to build their MMDVM repeater. Key components So to build GB7PP I opted for the following: Gateway Controller: STM32-DVM-USB MMDVM interface (N3XCC) This is a shield interface which sits onto the GPIO pins of a Raspberry Pi. Its function is to link the Raspberry Pi and the two radios, so they can communicate with the software. UHF DV Repeater: 2x Motorola GM350 (128 channel version) These are fairly cheap, built like a brick, and capable of long periods of transmission without over heating issues. It is important to get the 128 channel version if you want to plug your gateway controller straight in without further modification. Software: Pi-Star (MW0MWZ) & MMDVMhost (DG9VH) This is an outstanding piece of free software that Andrew keeps up to date. It has all the functionality you require to set up your MMDVM repeater. Gateway Server: Raspberry Pi 3 B+ The Raspberry Pi is small, cheap and ideal for running Pi-Star software on. You will require 5 volt power to run the Pi and also a suitable SD card to download Pi-Star software onto. Internet connection: Origin Fibre Broadband - 40Mb on BT Infrastructure The choice of internet is relatively unimportant but it should be as quick as possible to achieve a good link to the various digital networks. GMSK Remote Switch : Belkin WeMo This is a device which allows for remote switching of the repeater power. This is achieved via a mobile phone app. A requirement of the licence conditions in the UK is to be able to remotely shutdown the repeater. You can also shut down Pi-Star from within the software but this only shuts down the software not your transmitter. Antenna: Diamond X-50N Vertical Collinear (+7.2dB) Nothing fancy but good enough to transmit a reasonable signal. Beware if you hope to put your antenna on a third parties property or mast they may require a commercial grade of antenna and coaxial feeder. This can be cost prohibitive if you are doing this on your own. Duplexer: Procom 6 Cavity UHF (-1db) This enables a single antenna to work with both transmitter and receiver at the same time. These are tuned to the TX and RX frequencies so don't buy this until you have confirmation of your frequencies from OFCOM. Tuning these can be an right pain if you pick the wrong frequencies. Band Pass Filter: Procom BPF 70/3 on TX line (-1db) The key function of the BPF is to prevent interferance of the TX signal onto the RX frequency. These are also tuned to the TX frequency so like the duplexer don't buy this until you have confirmation of your frequencies from OFCOM. LNA Preamplifier: LNA 70cm-EME by VHFdesigns.com on RX line (+18db) This simply increases the receive signal so weaker stations can access the repeater. What next? Once you have your location, your licence you can order your duplexer and band pass filter. The next part just requires time and some help. You need to put up your antenna at the chosen location, interface your Raspberry pi, Gateway controller and two radios. Don't forget that you will need to program your radios with the RX and TX frequencies. Remember to set the power level as set in your licence. Get your setup right and you will have a great repeater which enhances our hobby.