Today in the car, scanning of the LW and MW bands stopped at a frequency of 277 kHz. I decided to find out where it is located and why it can be heard well.

Locator beacons are used in civil aviation for instrumental approach to landing aircraft, for precise access to the end of the runway.
НавNavigation radio systems are declared in Section 6 of Annex 10 of the International Civil Aviation Organization ICAO "ANNEX 10 - VOLUME II 6-1 11/10/16 CHAPTER 6. AERONAUTICAL RADIO NAVIGATION SERVICE".

NDB beacons radiate equally in all directions (non-directional) and operate in the long and medium wave frequency range (between 190 kHz and 1750 Khz), where the carrier and identification signal (1-2, less often 3 letters) are transmitted in slow Morse code. Beacons are installed near airfields for more accurate pre-landing maneuvers by aircraft. The aircraft has a device - a radio compass. When its arrow deflects 0°, the aircraft is pointed with its nose directly at the radio beacon. The deviation from the direct direction in degrees is called bearing.For example, if the relative bearing direction is 90°, the beacon is located to the right (at 15 o'clock) regardless of the magnetic declination.

Beacons for aircraft are divided into long-range and short-range. The far beacons are located at a distance of up to 10 km from the runway, the closer beacons are located near the end of the runway. The plane first flies in the far drive area, on the landing line above the near NDB.

2.16. The installation of the OPRS at the airfield is carried out on the extension of the runway axis at a distance of up to 10 km from the runway threshold. ...
2.17. The landing system equipment consists of two MRM* drive radios (long-range and short-range) and is designed to drive the aircraft to the airfield area, perform a pre-landing maneuver and approach.

Federal Aviation Regulations "Radio technical support for aircraft flights and aviation telecommunications"

Correspondence of call signs and frequencies of Pulkovo Airport:

277 kHz - long-range drive of band 28L, call sign "PO" 
572 kHz - near drive band 28L, call sign "O" 

342 kHz - long-range drive of band 10R, call sign "PK" 
700 kHz - short drive band 10R, call sign "K" 

326 kHz - long-range drive band 10L, call sign "PU" 
625 kHz - short drive band 10L, call sign "U" 

525 kHz - long-range drive of band 28R, call sign "PL" 
960 kHz - short drive band 28R, call sign "L"

Location of Pulkovo beacons in the DV-NE ranges on the map:

• MRM - marker radio beacon.

Frequencies, call signs and coordinates of radio beacons for Pulkovo Airport were obtained from open sources:
Pilotnav.com: airport ULLI
Jeppesen St.Petersburg Russia / ULLI/LED / Pulkovo

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