Russian SRO transponder modes

[Sarix]

Hello. I've been looking around the cockpits in various Soviet/Russian aircraft. They all seem to be carrying some kind of (maybe even the same model?) of SRO transponder with four different modes: АВТ (auto?), КД ("KD", in the English Hind cockpit this translates to "CA"), ±15 and КП ("KP", translated to "CS").

Is there any public information on what the four modes do or how do they differ from one another? 

Thanks!

[N49]

(I just wanna preface this first, I'm more acquainted with SRO-2 and SRZO-2, so my knowledge of PAROL is fairly limited, like many other people)

For PAROL, aka "PASSWORD", which is installed on the Ka-50, Mi-8MTV2, Mi-24P, Su-25T and A, Su-27, Su-33, and MiG-29A and S in game. Su-27, Su-33, and Ka-50 use the same IFF controller 480-I; MiG-29 uses the SRO-1P Product 6201 (also 6201R = SRO-1P for export aircraft) controller; Mi-8 alongside Mi-24 use a controller I don't know the name of yet. Operations of the IFF system are still not fully known, at least to me, BUT, here is what i know for those modes of function. 

Most of my information comes from a Su-27SK manual, training doc for new beginners learning about PAROL and its function alongside history, and the Soviet/Russian IFF topic on the SecretProjects forums. 

For the Responder:
(Keep in mind there are many controllers for this IFF system, but they all perform the same functions) The Block 480-I installed in the Su-27, apart of 6202 (SRO-2P) Radar Responder, controls the IFF system and how it functions up to the VII radar wave range. There is a separate rotary switch near the main controller in the cockpit that will manually control which wave band is used for the IFF system, this is the rotary switch with I, II, III-1, and III-2 on its panel.

These modes of function are:
Button with round red cover: СТИРАН → ERASED (Connects electrical circuit that detonates explosive cartridge within the IFF system to ensure secrecy).
Switch with red cover: БЕДСТВ → DISASTER/DISTRESS/EMERGENCY (Emits signal within the IFF code to show an emergency with the pilots aircraft when interrogated).

Switch:
ЗАПАСН(ОЙ) → SPARE: For changing the response codes.
and
РАБ(ОЧИЙ) → SLAVE/WORKER(Potentially meaning: Manual?)

Switch:
I and II → This is for switching the control codes, although the control codes are automatically operated by the aircraft, hence why there is a bar in front of this switch, often kept in the I position. For this to change, it has to be manually changed by the groundcrew in aircraft preparation. The I position in use with the SPARE position is used for signals in the "UP" wave range.
Theory: The II station may be for wartime use only as that's the only reason I could see it being blocked like that. Something similar was done to SRO-2 Block/Unit 8 controllers which included bar projections within the rotary switch handle that prohibited the code change from two numbers. On my 8A controller, it prevented the change of the code station except for 5 and 6 (which were standard flying operation IFF codes, codes 9-12 on the other hand were for wartime).

Rotary Switch:
АВТ → AUTH, More than likely means AUTO. 
THE REMAINING MODES PROVIDE MANUAL CONTROL:
КД → KD : This will turn on the KD Light.*
±15 → NO IDEA, I have some info that says KD-KP is used for switching from the current code to the subsequent code so probably this?
КП - Командный Пункт → KP - Command Post: This will turn on the KP Light.* Maybe this is used by the leader of a pair of planes?
*From my manual, it states that these lights do not present any function but I assume the modes KD and KP perform some function, the lights just indicate that mode is on. The manual also does not explore their meaning nor function sadly.

Either way, these modes just describe to other aircraft, or more likely ground-based radars and AWACS, the state of the plane for greater information to be provided to said Units. Information normally given by PAROL to friendly radar units are: Unit, Tail Number, Fuel Left, and Aircraft Reregistration (Make and Model). There is also one more potential meaning behind KD and KP, I did read in another manual (which was for SRO-2M) that the use of the same IFF code is not permitted to go over 30 minutes and must be changed after that amount of time, to ensure secrecy and make the aircraft harder to pinpoint by enemy radar systems. The aircraft technician will also go over this and when to switch the IFF codes during the flight with the pilot before take-off.

Fun Fact: There are multiple PAROL's! PAROL-1 is the interrogator (ЗАО-П), PAROL-2 is for aircraft, PAROL-3 is for naval ships, PAROL-4 is for ground-based radar systems, and PAROL-5 is for land forces.

[Sarix]

On 9/18/2022 at 1:38 AM, N49 said:

(I just wanna preface this first, I'm more acquainted with SRO-2 and SRZO-2, so my knowledge of PAROL is fairly limited, like many other people)

For PAROL, aka "PASSWORD", which is installed on the Ka-50, Mi-8MTV2, Mi-24P, Su-25T and A, Su-27, Su-33, and MiG-29A and S in game. Su-27, Su-33, and Ka-50 use the same IFF controller 480-I; MiG-29 uses the SRO-1P Product 6201 (also 6201R = SRO-1P for export aircraft) controller; Mi-8 alongside Mi-24 use a controller I don't know the name of yet. Operations of the IFF system are still not fully known, at least to me, BUT, here is what i know for those modes of function. 

Most of my information comes from a Su-27SK manual, training doc for new beginners learning about PAROL and its function alongside history, and the Soviet/Russian IFF topic on the SecretProjects forums. 

For the Responder:
(Keep in mind there are many controllers for this IFF system, but they all perform the same functions) The Block 480-I installed in the Su-27, apart of 6202 (SRO-2P) Radar Responder, controls the IFF system and how it functions up to the VII radar wave range. There is a separate rotary switch near the main controller in the cockpit that will manually control which wave band is used for the IFF system, this is the rotary switch with I, II, III-1, and III-2 on its panel.

These modes of function are:
Button with round red cover: СТИРАН → ERASED (Connects electrical circuit that detonates explosive cartridge within the IFF system to ensure secrecy).
Switch with red cover: БЕДСТВ → DISASTER/DISTRESS/EMERGENCY (Emits signal within the IFF code to show an emergency with the pilots aircraft when interrogated).

Switch:
ЗАПАСН(ОЙ) → SPARE: For changing the response codes.
and
РАБ(ОЧИЙ) → SLAVE/WORKER(Potentially meaning: Manual?)

Switch:
I and II → This is for switching the control codes, although the control codes are automatically operated by the aircraft, hence why there is a bar in front of this switch, often kept in the I position. For this to change, it has to be manually changed by the groundcrew in aircraft preparation. The I position in use with the SPARE position is used for signals in the "UP" wave range.
Theory: The II station may be for wartime use only as that's the only reason I could see it being blocked like that. Something similar was done to SRO-2 Block/Unit 8 controllers which included bar projections within the rotary switch handle that prohibited the code change from two numbers. On my 8A controller, it prevented the change of the code station except for 5 and 6 (which were standard flying operation IFF codes, codes 9-12 on the other hand were for wartime).

Rotary Switch:
АВТ → AUTH, More than likely means AUTO. 
THE REMAINING MODES PROVIDE MANUAL CONTROL:
КД → KD : This will turn on the KD Light.*
±15 → NO IDEA, I have some info that says KD-KP is used for switching from the current code to the subsequent code so probably this?
КП - Командный Пункт → KP - Command Post: This will turn on the KP Light.* Maybe this is used by the leader of a pair of planes?
*From my manual, it states that these lights do not present any function but I assume the modes KD and KP perform some function, the lights just indicate that mode is on. The manual also does not explore their meaning nor function sadly.

Either way, these modes just describe to other aircraft, or more likely ground-based radars and AWACS, the state of the plane for greater information to be provided to said Units. Information normally given by PAROL to friendly radar units are: Unit, Tail Number, Fuel Left, and Aircraft Reregistration (Make and Model). There is also one more potential meaning behind KD and KP, I did read in another manual (which was for SRO-2M) that the use of the same IFF code is not permitted to go over 30 minutes and must be changed after that amount of time, to ensure secrecy and make the aircraft harder to pinpoint by enemy radar systems. The aircraft technician will also go over this and when to switch the IFF codes during the flight with the pilot before take-off.

Fun Fact: There are multiple PAROL's! PAROL-1 is the interrogator (ЗАО-П), PAROL-2 is for aircraft, PAROL-3 is for naval ships, PAROL-4 is for ground-based radar systems, and PAROL-5 is for land forces.

I would guess (purely from the word) that РАБ would roughly mean "(normal) operation"... This is great info, much appreciated!

[N49]

Yeah, it's all very interesting and sadly its so hard to find official documents/manuals on the internet about the system itself unlike Silicon-2. At least from my delving into the subject. 

 Anyway, finally got my special package (; so here is some better photos of the 480-I controller (along with a heritage photo with the previous generation of IFF, Silicon-2): 

[Seaeagle]

On 9/21/2022 at 11:43 PM, Sarix said:

I would guess (purely from the word) that РАБ would roughly mean "(normal) operation"... 

Yes and "Запасн" in this case meaning "standby" (rather than "reserve" or "spare").