P-38, radios and antennas

[greatgonzo]

How should I understand the word primary in this sentance?

He tried to radio the control tower again for further directions, but discovered that ice had formed on his primary radio's antenna wire as he had descended through the overcast.

Whole text here:
http://www.pacificwrecks.com/aircraft/p ... 67638.html

Last edited by greatgonzo on Tue Feb 05, 2013 10:01 am, edited 1 time in total.

[Mike]

Primary = main radio
Secondary = backup radio

[greatgonzo]

This is an eye opener. Very interesting. Does it mean P-38 used to be equipped with two radio sets with separate antennas?

[43-2195]

The Lockheed P-38 "Generally"used only two types of radio, the early models had the SCR274N and the later models used the SCR522. The SCR274N used Two Transmitter and three Receivers, The transmitters were set to fixed frequencies on the ground, but the receivers could be tuned from the cockpit. I own a complete SCR274N radio. I'm not too familiar with the SCR522, but it was an improvement over the SCR274N and was equiping all new AAF Fighters by 1945. As far as I am aware both radios used only one antenna, controlled through an Antenna relay unit. I have all the original operation and maintenance manuals for the SCR274N if you want more detailled information.

[greatgonzo]

That's the way I have seen it. Not with these details, though. Still makes me wonder how to understand 'primary' here. I have seen the term 'primary radio' connected with some comertial stations, which makes only more confusion here.

Thank You very much for Your help so far.

[Taigh Ramey]

The SCR-274N was low to high frequency and used a long wire antenna. The SCR-522 was a very high frequency set that used an 'ax handle' antenna or vertical mast AN-104. Two very different antennas for two very different sets using very different frequencies.

One set didn't replace the other as an improvement but were used as defined by tactical communication needs in the theatre of operations.

Usually fighter aircraft would have either a SCR-274N or a SCR-522 but it is possible to have had both. Some 274N sets had one transmitter and one receiver with VHF capability but this seems to have been very rare in the AAF but common in late Navy aircraft in their equivalent set designated ARC-5. ARC-5's and 274N's with VHF capability had two antennas for each set but I don't think this sounds like what the original poster is referring to.

I know the original question isnt about a photo but it is pretty straight forward to figure out what radios are installed in an aircraft from a decent photo where you can see the antennas. If a P-38 or any fighter aircraft has a long wire antenna and an ax handle VHF antenna then it is possible it is carrying both sets mentioned above. There are other variations but these two sets were the most common ones used in Army aircraft.

Bombers were another story all together as they were capable of carrying a much larger compliment of radios and a radio operator as well as a pilot to work them.

[greatgonzo]

I've been reading Your posts about radios here and hoped for Your help. Thank You. I am still not sure of a couple of things here.

Some pics of PTO P-38s show both types of antennas mounted. When was SCR 522 introduced?
Would there be enough place for both radios on the shelf behind the pilot, or was there a possibility to mount one somewhere else?
Wouldn't a small navigation radio manufactured by Setchel Carlson and other manufacturers be a more probable explanation?

By the way, there are pics of 12th and 15th AF Lightnings with SCR-522 and both types of antennas. I always wondered if wire antennas on American MTO fighters could have been a result of using British IFF MkII system?

The very firsts P-38s use the nose mast antennas too, useless for HF radios one would say.

[43-2195]

I've never come across a P-40 or P-38 that carries both SCR274N or SCR522. AS you say greatgonzo, where would you mount both sets. Neither can I find both sets as being capable of being mounted (simultaneously) in any of the P-38 or P-40 Illustrated parts catalogs. My P-40 has a SCR274N which links to a AN-104 radio mast(via the antenna relay unit). My aircraft did not have the setchel carlson Nav radio, but the illustrated parts catalog shows that it was an option. I have a BC-608 IFF unit on my panel which I believe connects with the SCR274N to transmitt an IFF tone for 15 seconds every minute. The P-38F & G illustrated parts catalog does show the option of fitting the SCR535 or the SCR695, but I think these are earlier versions of IFF. I'd have to devot a bit more time(which I dont have right now) and read up on them.

[greatgonzo]

I'd be grateful if You did. No rush of course. Just when You will have a bit of time and felt like it, please remember there is a guy here interested. Those variants of radio equipment of American IIWW fighters are a bit mysterious but very interesting matters. Patience I have plenty.
Thank You for Your input again.

[Taigh Ramey]

When was SCR 522 introduced?

I am not sure exactly but the SCR-522 was around in at least late 1942. I have some Wright Field communications that talk about specific radios for specific theaters that mentions the SCR-522 and it is dated November of 1942. The 522 was a British design that we adopted for many reasons and we still use the same VHF frequencies today.

Would there be enough place for both radios on the shelf behind the pilot, or was there a possibility to mount one somewhere else?

In the P-38 I think it would be tough to install both full radio sets behind the pilot but I bet it could be done. There were different versions of the SCR-274N set with as few as one transmitter and one receiver so this is also a possibility. There was room in the boom too as I recall this is where the IFF was mounted.

Mostly I have seen P-38's with either the 274N or the 522 but my guess that if you see both the VHF antenna of the 522 and a long wire then it could have been used with the BC-1206 receiver. The 1206 is a small portable receiver that covered the low beacon range and would have used a long wire antenna. Sometimes the AN-104 antenna was used simply as a mast to hold up one end of the long wire. Our PV-2 has two of these AN-104's and one is used for both a VHF antenna and a mast for the wire sense antenna for the ADF. The other end of the wire antenna is attached to another AN-104 but it is not used for VHF comm (but we can use it for our new GPS-comm)

The cockpit photos also tell the story. The majority of what I have seen show the SCR-522 control heads or the SCR-274N heads but to date I have not seen both. I certainly have not seen every cockpit photo available but look on the right side of the fuselage and you will see the push button control head of the 522 or the crank to tune head (three of them) for the full 274N. I would love to see if anyone can find shots of other radios installed.

Wouldn't a small navigation radio manufactured by Setchel Carlson and other manufacturers be a more probable explanation?

Yes the Setchel Carlson radio is likely the culprit. This radio is also known as the BC-1206 but there were many different variations of this basic range receiver radio made by several manufacturers. As far as I know they always used a long wire antenna because of their low frequency coverage. The lower the frequency the longer the antenna.

By the way, there are pics of 12th and 15th AF Lightnings with SCR-522 and both types of antennas. I always wondered if wire antennas on American MTO fighters could have been a result of using British IFF MkII system?

I am not sure about the frequency of the British MkII IFF system right off the top of my pin head but most of the US IFF gear used a rod antenna about 18 inches in length for higher frequencies and not a long wire. Once again the mast could have been used simply to hold up the wire antenna and nothing else.

The one thing I have learned is that nothing was strictly standard. There are definite trends and commonality but there are always exceptions.

To me, the mods or changes are fascinating by nature and with a lack of documentation as to why, it is a lot of fun to try and figure out what was behind the differences we see from the standard Technical Order's and production information.

The aircraft were built on the factory line and changes were made during that production process. Then the aircraft left the factory and may have gone straight to a modification center for additional changes. Then the aircraft were assigned for a theater of operations and possibly went to an additional mod facility for specific mods for the theater. Sadly I haven't come across a lot of documentation for all of the different mod centers and more specifically just what all they did to each type of aircraft.

Having said all of this it is sometimes hard to narrow down, by documentation, just what a combat aircraft had without its specific maintenance file or form 1A's. We can guess from factory docs, technical manuals, technical orders, photos, and by inspecting the aircraft if available for signs of what was installed throughout its history. The guys in the field were certainly ingenious in making the aircraft fit the need without letting any red tape get in the way and many of these mods impressed the tech reps and made their way into future production aircraft.

Necessity is the mother of invention.

[greatgonzo]

I don't know the frequencies too, but British MkIII IFF entered in march 1943 and it used the blade antenna . Former MkII used wires but stayed in service till '45. There were always availability problems with MkIII, especially abroad. I wonder if American IFF cooperated with British system. So I figured maybe USAAF had to use available British system. That could have explain why MTO aircrafts did use wire antennas, while first supported and closer to the source 8th and 9th AF's did not. The trouble is all I did was figure... .

I have changed the title of the thread, as it evolved a little.

[Taigh Ramey]

I have not seen any examples of the use of British IFF installed in US aircraft. We definitely did coordinate with them and developed compatible systems that developed throughout the war.

I believe one early IFF set was the pipsqueak that used a contactor instrument to utilize the SCR-274N set for IFF work. This early IFF would have utilized the long wire antenna since it was also used for normal command set communications. The P-40 recently found in the Sahara has one of the BC-608 contactor units in the panel.

Here is the document that I mentioned earlier which I found at National Archives titled Radio Installation In Fighter Planes In Accordance With Destinations. This document discusses what types of radios were designated for aircraft heading to the four theatres identified at the time. Very interesting look into radio policy in November of 1942.

[greatgonzo]

Great! Isn't a page missing here (C-2)?

Box 2/a:

Middle East fighters for both RAF and AAF should have British MKII IFF until SCR-695 system is installed, installation date indefinite yet.

It is a first sign of confirmation of my theory I ever met.

[Taigh Ramey]

You are right. I missed that! Oops...

My knowledge of early IFF especially the UK sets is slim to none...obviously... I would sure love to see installation photos in US aircraft if you come across any.

I also see that both the 274N and the 522 were used with the pipsqueak IFF and not just the 274N.

So was the US SCR-535 compatible with the British MKII? Did the MKII use low frequency and long wire antennas?

Great! Isn't a page missing here (C-2)?

C-1 is still a classified document so I cannot show it to you. Too bad too because it has all of the answers to those pesky questions all of us radio nerds have been wondering about...

Just kidding of course. Page C-1 isn't part of this document. When scanning docs at NARA I just named the images with letters in sequence so C-1 is actually a document about the SCR-518 radio altimeter. C-6 does discuss replacing SCR-535 with SCR-595/695 and the parts issues.

[greatgonzo]

So was the US SCR-535 compatible with the British MKII? Did the MKII use low frequency and long wire antennas?

I wouldn't know. But MkII surely used the wires (on Spitfire two wires from fuselage behind the cockpit to horizontal stabilisers), so it shouldn't have been VHF as communication radio was. Former MkI was a nuisance as it shared the HF wire antenna with pilots radio, and IFF signal used to cut the pilot off.
One would wonder why to use British IFF if SCR-535 was compatible?

The mixture of IFFs in MTO may explain the wiring mess there. Unfortunately it is written only in this classified document of Yours .

I would sure love to see installation photos in US aircraft if you come across any.

So would I, so would I... .