UM04 is a Bulgarian military station.

The transmitter site is near Bankya. (Google Maps). Barracks and a HF-RDF site are nearby.
Google Streetmaps shows antennae at this site.

On September 20th " 6BQY DE TYN7 K" was sent before the message. That was the first time that we heard tactical callsigns before a message.
Although we call the Bulgarian station Promrö, it's actually not correct as the Bulgarian language does not know umlauts.

The morse translates in Bulgarian ПРОМРЧ or its official transliteration PROMRCh. There seems to be no proper translation for this word.

Unid Bulgarian station with a daily schedule on 4735 kHz at 0700 UTC (summertime) or 0800 UTC (wintertime).

At least one or more tones are sent 5 to 10 minutes before the start of the transmission. The broadcasts sometimes start several minutes later.

The messages are hand-keyed.

After a pause of ~ 2 - 3 seconds, the message is repeated in full.

Depending on the operator it sends the date as = 0111 = or = 01 11 = and midnight as 2400 or 0000.

Sometimes = ABV = but most of the time = ABV.  ABV means "I repeat".

Reference:

All information is from Ary Boender's monthly newsletter, "Numbers & Oddities" Edition #300, September 2022.

Last editing of this page:   October 3, 2023