OVERVIEW:  The RSN-75MV aka S-75VM Desna aka SNR-75M4 aka S-75M4 Volkhov aka FAN SONG E radar is a trailer-mounted illumination radar for the SA-2D and SA-2F GUIDELINE SAM.  It operates in the NATO G- band (IEEE C-Band).

DETAILS:  The FAN SONG illumination radar systems is associated with the SA-2-series SAM.  The SNR-75 family of radars employ a complex antenna arrangement which is employed to provide range and angle tracking of the intended target, as well as the transponder beacon in the SA-2 missile, which is flown to a collision with the target using a command uplink embedded in the SNR-75 radar.

The antenna system consists of two pairs of antennas: A pair of electromechanically scanning (aka "Lewis-scanner") antennas provided  vertical and horizontal target search, usually conducted in conjunction with the battery's P-12 SPOON REST radar, made necessary because to the narrow, 7.5° x 1.5 °  surveillance beams of the FAN SONG radar could only be steered  through a 16° arc.  These perpendicularly mounted antennas created a cross-shaped beam that was centered on the target to determine its height and azimuth. These beams perform a characteristic 'flapping' motion as they scan their sectors. The FAN SONG radar had a dead zone at low altitude, which, unless covered by AAA, allowed attacking aircraft a potential avenue of attack. 

Unlike earlier models, the  FAN SONG E has two parabolic dishes mounted on top of the horizontal Lewis scanner.  These provide Lobe-On-Receive-Only (LORO) ECCM capability.

A UHF (0.3-1.0 GHz) parabolic antenna mounted on the right side of the array transmitted command signals to the missile, guiding it to the target.   

The FAN SONG is capable of engaging a single target, and had two missile uplink channels.  Deploy/Stow time was approximately 60 minutes.  The missile must pass through the guidance beam within seconds of launch in order for it to be acquired and steered to its target.

Specifications:

	Frequency:	5.01-5.06; 4.91-4.99 GHz (G-band (NATO))
	PRF:		828-1440 (search); 1656-2880 (track) pps 
	Power: 		 1 MW (peak)
	Range:		40, 80 nm (instrumented); 
	Accuracy:		60, 180 m  (est)
			
NOTES:  IOC 1960.  Associated with the SA-2D Mod 3 and SA-2F Mod 5 SAMs.  Radar used a variety of designations, including RSN-75MV, -75V, -75V1, -75V2, SNR-75M3 and -75M4. depending on associated SA-2 system. The RD-75 Amazonka was a range finding radar incorporated often in late model S-75 / SA-2 Guideline missile batteries. It was slaved in azimuth and elevation to the boresight of the SNR-75M3 Fan Song and was employed to perform precision range finding when the range finding channel in the Fan Song was degraded or compromised by jamming.


SOURCES:    Jane's Radar and Electronic Warfare Systems, "Fan Song missile control radars," 02 July 2001;  https://www.radartutorial.eu/19.kartei/11.ancient/karte030.en.html ; http://www.ausairpower.net/APA-SNR-75-Fan-Song.html; Steven J. Zaloga, "Red SAM: The SA-2 Guideline Anti Aircraft Missile" New Vanguard, pg. 41. ; Pike, John. "FAN SONG." GlobalSecurity.org. Last modified 7, 2019. https://www.globalsecurity.org/military/world/russia/fan-song.htm; NATO, "Current Soviet Electronic Equipment, Vol. C: Landbased, pg. I-C-13 (12 February 1969)


