Using an RTL-SDR to decode VOR Aircraft Navigation Beacons in Real Time

The blog content is updated while considering all the feedback and adding more clarity to certain sections. Now the source code is published in github.

Actually, the author is receiving a Doppler VHF Omnidierctional Range (DVOR) and not a (C)VOR as he describes in the text.
The location of the DVOR on 115.500 MHz is south-east of the runway center and not north of the runway as shown as end of radial. The DVOR can be found in google maps at 12°56’57.8″N 77°40’50.9″E, while ourairports.com identify 12° 56.982021′ N, 77° 40.859985′ E (2,908 ft / 886 m MSL) as the location for DVOR/DME BBG 155.500 MHz.
A DVOR consists of a large counterpoise with a ring of min 40 to today 50 Alford loop antennas in a circle around the center reference antenna. Simplified explanation for the difference between DVOR and VOR is:
-DVOR switch one signal between opposing antennas, rotating 360° around the Doppler basis to produce the doppler effect, while the center antenna is used as reference antenna,
– VOR initially had 4 and later 5 Alford loops on a counter poise in the FAA designs, while later designs from other manufacturer consist of 2 or more separate vertically stacked antennas for generating the horizontally polarized rotating and reference signal. Reference and rotating cardioid generation are exchanged between DVOR and VOR. The rotating cardioid was first generated by a motor driven goniometer. One design used a short horizontally dipole driven by a motor, inside a polarization cage to ensure only horizontally polarized radiation was generated.
Alford loop antenna are horizontally polarized omnidirectional antenna design described by Alford first in electronic design ~1940.
VOR and DME are ICAO standardized navigation aids since 1949, and are defined in ICAO SARPS Annex 10, and later in Annex 10 Vol.I. Note: the 1949 DME was replaced later, since 1960 by DMET (T for TACAN based parameter, without that ICAO adopted the bearing information from TACAN) which are called today DME/N (for a narrower signal than DME) and DME/P (Precise).
For difficult terrain DVOR development started about 1955 in USA, UK (e.g. Plessey) and Germany (Alcatel for BFS), with mature DVOR designs in operational use since the early 1960’s. Counterpoise diameter and height AGL varies. If the author has direct Radio Line Of Sight, that the displayed radial should not fluctuate so rapidly.
If this is for an academic paper it shows bad research on the authors part, and obviously lack of understanding on his professors part, when the difference between VOR and DVOR is not identified. The author describes generation of a VOR signal, while he should describe DVOR generation. Adiagramm can be found e.g. in FAA R&D report CT-81/194, TEST AND EVALUATION OF SOLID-STATE DOPPLER VERY HIGH FREQUENCY OMNIDIRECTIONAL (DVOR) DISTRIBUTOR ASSEMBLY
PS.: The year numbers that I quoted are from memory.