Coordinated vintage radio activations (“PRT” = Perinneradiotoiminta in Finnish) started in Finland in 2006. To this day there are about 40 radio amateurs operating stations with a wide selection of vintage transmitters, receivers and transceivers at least twice a year. There are two large scale events; one on Independence Day (6 December) and a second on Finnish Defence Forces Day (4 June) with additional activities running throughout the year with many operators using the equipment on a daily basis. The main features of the equipment and equipment specifications as well as radio traffic are described below.
The equipment used in connection with the PRT activities comes mainly from the World War II era. Some later “Green Line” equipment is also used, since the PRT criterion is that the original design should be more than 40 years old. On this basis and easily qualifying in terms of “age” are older radios coming back to the 1930s are also active in these special events.
During 1939 to 1945 the Finnish Army mainly used radio equipment with a frequency coverage of 3-6 MHz. Most equipment was manufactured in Finland but US, German, Swedish, Hungarian and even captured Russian equipment was also widely used. This old 3-6 MHz radio equipment can easily operate within the 3.5 MHz and 5,3 MHz radio amateur bands. 7 MHz and 1,8 MHz bands are available with some equipment types. Actually obtaining spare parts, tubes and schematic diagrams is an immense challenge to restore these old radios back to their former glory.
The most famous Finnish wartime radio station is a small portable CW transceiver called Kyynel (which translates as “Tear” – as in tears from the eyes). It was designed for commando and agent operations. VFO-equipped, the Kyynel uses the frequency range 3.5-6.0 MHz, and achieves a power output up to 0.5 Watts.The transmitter of this battery powered transceiver is watertight and is constructed on the transmit side with only one tube, a double pentode DLL 21. The three-tube receiver is regenerative ie tuned radio frequency, TRF. One special feature is that the antenna is tuned to transmitter frequency by means of varying the length of the antenna. With utmost simplicity of construction and operation, its reliability and small size were the key features of Kyynel. The Red Army had a secret agent transceiver called Sever (which translates as “North”) which was somewhat similar to Kyynel. Several Kyynel stations have been restored are now active in PRT special events. Some Sever stations are to be found in Finland and will most propably soon be in active PRT operation. Some older Soviet field stations of the “6PK” type, dating from the mid 1930-ies, have already restored and will be in operation in future.
Finnish VRGK and VRFK (“Celsius”) units are battery-operated portable stations, which use the frequency range 3-6 MHz. (VRGK 4.6-6.6 MHz), and have an output power of 1-2 Watts. The tubes are of the -21 series like DLL 21, DF 21 and DF 22. Both radios can be operated on CW and AM. Several VRFK stations are active in PRT, some of them throughout the whole year. At least three VRGK stations have also been restored.
VREH (”Bertha”) is an accumulator/230 V 50 Hz mains-operated portable and fixed radio station. If in portable operation, the receiver is battery-operated, with the transmitter being powered by means of a 12 V=/500 V= dynamotor. The frequency range of the transmitter is 1.5-6 MHz in two bands, and the receiver also has LF – and MF – bands receive capability. The tubes within are PE 05/15 (transmitter) and German 11 series steel tubes, like EF 11 and ECH 11. The transmitter’s output power is 15 – 20 W on CW and 6 W on AM. Several VREH stations are active in PRT on 5,3 and 3,5 MHz bands, some on 1,8 MHz.
VRLK is is a wartime constructed communications receiver. Its general features were based on the famous National NC-100XA with a horizontally moving coil carriage, scale mechanism and front plate lay-out however unlike the NC-100 XA there is no crystal filter included in the design. Powered by battery plus accumulator or 230 V AC mains its frequency range is 223 – 20200 kHz however there are no MF bands available in the receiver. Both VRLK and NC-100 – series receivers are widely used in PRT activities.
US WW II surplus equipment as well as German equipment are in evidence during PRT. notably the Command Sets of SCR-274 – series and German Luftwaffe stations of FuG 10-series.
The majority of the WW II equipment was VFO – based. Interestingly it should be mentioned that back in the day, Finnish radio amateur OH2NV started in his own workshop small – scale manufacturing of the crystals to meet the pressing needs of the armed forces. (E.g. a later version of “Kyynel” was was designed using crystal control) Some of these homemade OH2NV – crystals are in use even to – day.
During the special activity days on 6 December and 4 June a co-ordinating team gives recommendations for frequency allocation. Transmitter power is advised to be below 30 Watts with the mandatory limit of 15 Watts on 5,3 MHz. Among special activity days is March 5, 2018, 100 years of Signal Corps in Finland.
The activity is generally on the 3.5 MHz amateur band, but some stations are also found in the 1.8, 5,3 and 7 MHz bands. Vintage stations can be initially identified where the may add the letter “S” to their call; e.g. OH3XYZ/S. Stations using WW II equipment may add “SA” to their call sign. Both CW and AM modes are used.
Outside the PRT activity periods daily CW contacts and tests can be made on the spot frequency of 3556 kHz in the 80 m band. Additional frequencies are also used ie 3565 kHz (reserve frequency 1) and 3560 kHz (reserve frequency 2) as well as 5356 and 1837 kHz. Radio amateurs from countries outside Finland are heartily welcome to take part in PRT activities.