Sofia Aero :

 

working with an aircraft (Rudy van Dalen, 1992)
here is a recording of Vidin working with Sofia (Rudy van Dalen, 1992)
Bourgas working with Sofia (Rudy van Dalen, 1992)
Silistra calling for Sofia (Rudy van Dalen, 1992)
Targovishte working with Sofia (Rudy van Dalen, 1992)
Varna working with Sofia (Rudy van Dalen, 1992)

 

here you can see the dipole with traps, used for domestic shortwave communications (rb, 1999)

 

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Frequencies Voice:
2974
2980
4651
5540
5622
10060
11245
11384
17961