Spitfire: IFF device and aerials

[Fernando]

Hi, all,

I have been wondering if the IFF device on Spitfires worked interlinked with the radio equipment. The answer is yes, and it has even been told that when the IFF was buzzing, radio com was cut off. But now, my question is: could IFF equipment be fitted independently of radio equipment? Or, if radio equipment was stripped off, it meant necessarily that IFF equipment was not present?

Regarding aerials: did those related to the IFF equipment run through the lateral wires?

Thank you all,

Fernando, from Argentina

[Troffa]

Hi Fernando,

The early "pip-squeak" system used during the Battle of Britain utilised the Spitfire HF radio to transmit a signal on a dedicated channel, seperate from the one used for voice, for a set number of seconds every minute, the signal was triangulated at Fighter control stations and allowed friendly formations to be tracked- a good web site here:

http://www.battleofbritain1940.net/document-14.html

Later in 1940 the Mark I IFF was introduced, and this was a system independant of the Radio and used the lateral antenna that you mention.

Good article here:

http://spitfiresite.com/2010/04/spitfire-m...-aerials.html/2

Cheers,

Troffa

[Chuck1945]

If I have correctly read the various posting on the subject of Spitfire IFF, then the late 1940 Spitfire II (1/72 AZ kit) I am finishing would most likely not have had a radio antenna wire from mast to tail, but would have the IFF aerials from the fuselage sides to the tailplanes?

[Troffa]

I would say that's a safe bet Chuck, the Antenna from mast to tail was deleted when the HF TR9 radio replaced by the VHF TR1133.

I would check for any pictures of the aircraft you wish to model to be sure.

cheers,

Troffa

[Edgar]

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Edited July 23, 2010 by Edgar

[bobgpw]

This intrigues me as I work with radar/ssr on a daily basis.

Edgar, from what I have read, the "Pip-Squeak" system appears to revolve around a clockwork mechanism that enabled the TR9 to use a voice channel and a "special" channel. The unit acts every 14 seconds to transmit on the special frequency. From this, ground stations can DF the aircraft. I suppose that this was most useful behind the CH network as there was no provision for CH type radar (RDF ) to look inland at this stage.

Can you tell me how the Mk 1 IFF fits into this? I can't see how the TR9D set has any TxRx facility for the Chain Home radar IFF equipment. The only Mark 1 IFF drawing I can find doesn't tie up with any of the circuitry in the TR9D. Did the Mark 1 IFF have an ARI designation? Pip Squeak appears to be a bit like modern ADS-B, in as much as the aircraft constantly transmits whilst the set is switched on (and fuly wound!!). The IFF Mk 1 in contrast is a passive respondeer in that it only transmits when interrogated. That said, flying in the CH environment, everything and everyone gets illuminated - like it or not.

From my limited knowledge of the wiggly amps, the IFF Mk1 works by being floodlit by the CH radar frequencies of 20-30Mhz. This causes the unit to transmit the pulse back to the radar at a greater amplitude (super-regenerative responder). On the cathode ray tube, the operator would see the time base deflect down and be of greater amplitude than non-IFF aircraft. Am I going the right way so far?

It appears that Mk1 IFF was tricky to use in a single crew environment.

Fascinating stuff that we take for granted today.

Bob

[Edgar]

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Edited July 23, 2010 by Edgar

[bobgpw]

Thanks Edgar,

I happened upon a diagram of Mk. 1 IFF and an assertion that 1000 sets were built. As you say, the TR9D only has provision for "Pip Squeak" and the mechanical contactor assembly. I presumed that IFF Mark 1 was separate to the TR9D unit. If it needed to be tuned to the radar frequency I presumed that there would be some form of tuning device in the cockpit. I too found the R3002 IFF set, but for what it is worth that appears to be Mark 2 IFF??

Yes you are correct regarding CH, but most stations had a reflector assembly fitted behind the dipole transmitter aerial. This prevented unwanted radiation behind the aerial curtain although a small back lobe would form. Just like today, the CH utilised lobes generated by the Tx array. For this reason, the ground in front of the Tx array had to be reasonably flat to allow the lobes to form. You would find a similar set up today in front of an ILS installation at a UK airfield.

Anyway, I digress, it is just amazing that we had such brilliant scientists and radar operators during 1940.

Bob

[Troffa]

"Aircraft were using the Mk.I I.F.F. (which, in the Hurricane, at least, was clockwork,) from April, 1940, and despite what the "experts" say, appears to be the "Pip, Squeak" equipment, when it was used outside the radar system."

Edgar, thanks for the usual hubris.

Pip-squeak was not IFF MkI.

As for the elusive details of the development of IFF and the antenna system for the Spitfire try "google"

http://www3.sympatico.ca/drrennie/radar.html Chapters 2-4 in particular.

Mark

[Edgar]

The Mk.I I.F.F. was R.3000 (possibly 3001, as well, but that's unproven.) There are no files, on it, in Kew, except bare mentions of it being tested as early as 1939, plus a report of one causing interference to "its attendant TR9D." Whether "attendant" means near to, next to, or attached to, will have to remain a mystery, for now.

The R.3002 was the I.F.F. Mk.II, as was the R.3003 (3002 was 12v., while 3003 was 24v., and was tested during the summer of 1940, which (more or less) ties in with Supermarine not fitting it until the end of December. Bob, if you'd like them, I have details, parts lists, and circuitry, for the Mk.II, at present in the camera, but nothing on the Mk.I.

None of this helps you, much, Fernando and Chuck, but the total lack of any mention of R.3000, by Supermarine, suggests that the fitting did not cause much (or any?) disruption to production (unlike the R.3002, which had a mod all to itself,) so, like the Hurricane, could have been entirely inside the fuselage. I have some photos of a damaged (due to detonator experiments) box, but they do not appear to give a clue as to how it worked.

Edgar

Edited July 25, 2010 by Edgar

[Edgar]

Found this illustration of the Mk.I

And this is a photo, in a series on the effects of explosives

This is part of the Mk.II

And this is the other piece

Edgar

Edited July 25, 2010 by Edgar

[Troffa]

Edgar,

I do not take any delight in your discovery, as I was already aware of the operation of pip squeak (Which in fact is nothing more than a High frequency Direction Finder or Huff-duff in RAF parlance) and IFF Mk1 which as Bob stated is a super-regenerative transponder which re-broadcasts at a modulated amplitude the received Radar signal.

My initial ire was directed at your statement “despite what the ‘experts’ say appears to be the “pip squeak system”

Now for someone such as yourself, unfamiliar with Radio and Radar technology (as you remarked in your now deleted post), this seems to me as somewhat of a bold statement.

A statement which given your unquestionable authority on the Spitfire, might be taken as the last word on the subject by many of your readers. (your pejorative use of “Experts” doesn't help either)

As I was aware that the statement was not correct I used the term “hubris” (King Lear anyone?) which in my dictionary (Oxford Concise 9th edition) is defined as “Overbearing pride or presumption;” and I believe that your statement was an example of overbearing presumption.

Your research and input is always of interest to me, and I look forward to any future discussions to which I feel I can make a contribution.

Thanks for posting the AP images.

Regards,

Mark