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Old 04-09-2020, 06:42 AM   #11
saburo_cz
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Allied IFF systems first used ground radar frequency as a trigrer for answer.
Plane was equipped with receiver which receided radar signal and then re-transmits this signal back. It just increased echo on radar screen.
These IFF were Mark I and Mark II, btw. MK.II operated on SRC 268 and 270 radars frequency range (probably more).

Because of increased frequency range used by ground radars (but not only) Mark III was developed. The IFF transmitter (interogater) was separed from radar hardware and frequency.
The IFF transmitter generated and sent signal through own antenna and plane transponder automatically transmitted replay.

Both systems were totaly separated from plane communication radio.

More IFF systems were in development or developed, but these above were used mainly.
MK.III is for P-51D, P-47D and Spitfirre Mk.IX era.
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Old 04-09-2020, 07:02 AM   #12
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What if someone forgot to turn IFF on or combat damage knock out IFF, did he get shot while approaching airfield ??
It would be nice feature that friendly AAA may open fire to allied plane, it happen quite often iirc.
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Old 04-09-2020, 04:45 PM   #13
71st_AH Rob
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Quote:
Originally Posted by vanir View Post
I'm by no means a technician but I have some corrections based upon what I've managed to figure out over the years from an armchair.

40s vintage IFF is a radio transponder set installation, nothing to do with radar but was an extension of the essential radio navigation network, which started off as simple beacons in the 20s and was becoming more complex through the 30s and during the war. In the early war for example, when tallied 50% of all combat losses for the RAF were due to navigational error and mechanical failures and no other reason. In one case an entire bomber stream was lost when it accidentally headed towards Norway instead of returning to base. This may seem shocking or unreal to modern thought but was completely commonplace during the period and punctuates how important the (international) radionavigation network was for aeronautics worldwide.
So radio beacons and increasingly a more complex radio navigation network existed throughout Europe in the 30s-40s, even in the Soviet Union although they lagged behind updating equipment and had simple beacons until about 44, meaning lend lease aircraft had more radio equipment installed than Russians could actually use and it was one of the things they loved about them in preference to their own aircraft, so many radios installed they didn't even know how to use some of them.
Anyway vintage IFF is a simple radio transceiver which automatically responds to a signal challenge typically transmitted by a ground station in the radio navigation network, ie. it is a radio transponder.

More modern transponder/ground station systems are commercially referred to as "passive radar" but are exactly as before, just a radio signals network primarily for navigation, but they add more information and are no longer just a simple "squawk" but actually transmit some instrument data (IAS, Altitude and Heading), as well as ID (type or flight number and operator), whilst the radionav network intrinsically provides its current position. Thus it gives all the necessary information an active radar would give, but it is not observational, it is a radio call making some claims and a ground station operator believing them, all his instruments actively tell him is current position of a squawker, the aircraft's transponder is telling him everything else. Passive radar is more like virtual radar, it was conceived essentially as the poor man's radar for smaller airfields that couldn't afford active radar to still perform tracking and traffic management independently of local radar stations which often have other tasking. Another idea that came as an extension of the radio transponder is the collision avoidance system, as computerization of flight management developed the manners in which a radio transponder can be used for the benefit of the aircraft increased.

Modern military IFF is not used the same way being integrated into the computerization of modern warfare, using a variety of tools at its disposal for something a little more involved, including radar and mission Intelligence systems such as datalinked local air traffic information on painted targets, piped though the base operator and/or AWACS to the pilots.

In WW2 some late war fighters had a radio set update capable of transmitting an IFF transponder challenge directly but again, nothing to do with radar, just a radio signals exchange, a squawk amounting to a radio fingerprint identifying the operator with some basic electronics: 15ohms lights orange bulb, 25ohms lights blue bulb, different squawks impede circuit differently to determine result, something like that.

It appears that your understanding of early IFF and RADAR is basically flawed. IFF is fundamentally tied to RADAR and was developed expressly to operate with it to allow operators to more quickly differentiate friendly contacts from enemy contacts. The modern Transponders that civilian aircraft use today, both Commercial Air and Private, developed from Military IFF to take advantage of the system as both a way for ATC to differentiate contacts and as an aid to navigation.



You have confounded Radio navigation with RADAR. RADAR is "RAdio Detection And Ranging." Both are based on transmissions in the Radio band of the electromagnetic spectrum. The first operational Allied IFF utilized the RADAR signal, amplified and returned it using a transceiver to differentiate Allied a/c from En on the RADAR Operators CRT. The Soviet Union used this system up until it fell. The Western Allies went to a standard frequency for IFF since different RADAR types worked on different frequencies. You could have a situation where Chain Home identified a contact as friendly because it received the correct signal back and a Type 14 RADAR would not and therefore identify the contact as hostile. Modern military IFF is essentially the same today but can give more information if the correct modes are activated, tail number, a/c type etc. More complex information is transmitted digitally by EPLRS/Link-16/etc and is not part of IFF.



DCS takes an Arcade approach to IFF, inherited from FC3, basically if your tracking RADAR locks on an En a/c it will display a different symbol on the HUD than if it is a Fr a/c. Some of the newer a/c have some rudimentary IFF systems and a more realistic representation of IFF can be simulated outside of DCS using Simple Radio Standalone (SRS) and Lock-On tiny ATC (LotAtc). SRS will, if the DCS module simulates it, transmit the IFF information from the DCS export function to LotAtc using range and line of site to display on the so the controller can see the information that would be transmitted. LotAtc with SRS allows a basic simulation of Ground Controlled Intercept (GCI), which is what IFF was used from in WWII, as well as ATC and Precision Approach RADAR (PAR).
So for Korean War Era and earlier, we can simulate IFF if the module has it modeled and SRS can detect the information to pass to LotAtc. For Air to Air IFF, we need to rely on the Mk I Eyeball or ask the GCI for confirmation that the contact we are tracking is enemy just like they did in real life.
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Old 04-09-2020, 10:51 PM   #14
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Quote:
Originally Posted by grafspee View Post
What if someone forgot to turn IFF on or combat damage knock out IFF, did he get shot while approaching airfield ??
It would be nice feature that friendly AAA may open fire to allied plane, it happen quite often iirc.
IFF was mainly utilized by command centers trying to direct the air war on a national level, which had map tables on which friendly or enemy aircraft were projected as red or green dots, but not by manually aimed AAA defending airfields or ground forces. Hence the bright red underbellies of Fw-190D9s defending Me 262 airfields or the high German losses due to their own flak during operation Bodenplatte.
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Old 04-11-2020, 01:59 AM   #15
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Quote:
Originally Posted by vanir View Post
{...} look up technical descriptions of modern commercial airport "passive radar" or just watch a few episodes of Air Crash Investigations (Mayday: Air Disaster in the US), they describe its technical functions quite frequently throughout the series as it is an important factor when aircraft are lost, since it is not first hand information. As I described the aircraft transponder sends instrument data and identification to the ground, which can only read the position of the transponder signal because "passive radar" is just the more modern radio navigation beacons and aircraft transponder interacting and isn't actually any kind of radar, but is a colloquial term for a radar simulation using data that should, but isn't necessarily accurate.
When an airport loses a contact on "passive radar" they contact the nearest actual radar station, usually a military base and they locate the lost aircraft for them if it is still in the air.
When I asked for references, I meant for you to provide the sources or links that you got for your information. And the reason for asking was that your information seems either rather mixed up or incorrect. As it was at odds with what I am finding with internet searches led me to inquire. Also, I was more after academic, technical or encyclopaedic references, that I could follow-up on, not television dramas.

As for technical descriptions of passive radar... Passive radar is the determination of a range and direction where the receiver is not in control of the transmission. Thus it is a form of parasitic radar, which can exploit other transmissions. There was passive radar used during WWII, such as the Klein Heidelberg Parasit radar. However, this is not an IFF system, but is making use of (enemy) radar transmission received by a (friendly) "passive" receiver. References:
https://pdfs.semanticscholar.org/3f7...b4ebf03ca6.pdf
https://www.cdvandt.org/k-h.htm
https://www.geschichtsspuren.de/arti...sstechnik.html


I am guessing that your idea of IFF is more related to modern aircraft "squawk" transponders? Something like this perhaps?
https://en.wikipedia.org/wiki/Transponder_(aeronautics)


But IFF, aviation transponders, (active) radar and passive radar are all different technical implentations.

Looking at something like the FuG 25a, this is replying to a set code that is being sent in conjunction with the radar. That is not passive, but active (interrogation) transmission.
https://en.wikipedia.org/wiki/Erstling_IFF_transceiver

I'm not sure about the Allied systems, hence my interest in asking.

Also, at this stage, all interrogations seem to be the "IF" out of "IFF". In other words, you are expected a code from a friend (not instrument data). An absence of a code (or signature signal) implies a foe. See the Erstling reference above.



Otherwise, see the things that @71st_AH Rob has written above. (Thanks, Rob, for that clarification!)

Both otherwise, picking up on what both @Cunctator and @71st_AH Rob have written, my impression is that although the IFF transponder is located in the aircraft and needs to be switched on, the real implementation of it would be at the F10 map / Combined Arms level.
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Old 04-17-2020, 06:42 AM   #16
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I learned something. Thanks Vanir.


Quote:
In WW2 some late war fighters had a radio set update capable of transmitting an IFF transponder challenge directly but again, nothing to do with radar, just a radio signals exchange, a squawk amounting to a radio fingerprint identifying the operator with some basic electronics: 15ohms lights orange bulb, 25ohms lights blue bulb, different squawks impede circuit differently to determine result, something like that.

Can you name any aircraft type ?

Last edited by rollnloop; 04-17-2020 at 06:46 AM.
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Old 05-05-2020, 03:26 PM   #17
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Didn't the Germans, at least, largely end up yanking it out of their planes though? I'm given to understand the allied bomber waves figured out their IFF squawk and just started using it themselves.

I suspect it probably partly worked in the Battle of Britain, but the whole radio system was not known for its reliability at the time, such that the RAF ended up doing that black and white underbelly scheme, simply to assist with the spotter core differentiating friend from foe.

And apparently the radios in the Pacific had even more problems... (Radio talk starts at 1:46:35 https://youtu.be/ApOfbxpL4Dg?t=6395)
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