P-51D-30 and H-5 extra radio aerials, what's their purpose?

[fsendventd 3]

I've been looking around at details on the 51's design for a project I'm probably going to start working on soon-ish, and realized something while researching all the changes made to the various models for the Korean War. The D-30 and H-5 models in War Thunder (and perhaps some of the others, but as I'm a US player I don't remember the details on the other nations) seem to have these odd double aerials on their rear fuselage.

I can't figure out what their purpose is, as all of the aircraft I've seen on Google Images just have a single one, or at least the D models do. What did the dual aerials add, and were they a field mod installed to later D models and standardized on the H? I know the D-5 only has a single one.

It's also lacking the underside aerial that the D-30 and H-5 have, shown here on a D-30.

Google also agrees with me in this respect, I've yet to find a D model with the underside aerial on the fuselages but the H seems to have it on the wing as it does here.
TL;DR: P-51D-30 and P-51H-5 have two extra antennae on them that I've yet to find the purpose of, and in the case of the D-30 that I've never actually seen on an aircraft. I can't find what their purpose is and if/when they were installed on later D models, and was hoping someone could help.

 

[Rapitor 10,650]

I found this, didn't dig much into it:

D-30/H antenna:

 

Early and "mid" Ds:

[AdelWolf 789]

ah thank you I was also wondering this.

So basically its antenna? Disappointed 

[Josephs_Piano 6,089]

the twin antenna on the -30 shown above are for the  AN/ARA-8 radio direction finder - the difference in signal strength between the 2 gives the direction the signal is coming from.

 

the APS-13 set that has the little aerials on the tail is a radar warning receiver

 

SCR-522 and -515 are "normal" voice radio transmit/receive units - they had 4 VHF channels

 

SCR-274 is a multi-channel voice radio sometimes called a "command set" - they could handle voice, continuous wave and tone-modulated signals, so included navigation and homing functions.

Edited October 9, 2020 by Josephs_Piano

[MILESPARVUS 1,095]

It's been a long while since I had the same question, but IIRC the dual antennas (plus the one forward) were a system that was installed mainly on Mustangs running very long range escort for B-29s flying out of Iwo Jima. It wasn't installed in Mustangs Europe (or vaery rarely, AFAIK), because they didn't need it there. Partly because the war in Europe was wrapping up when the system was deployed in April 1945, and also because Europe didn't have the same sorts of navigation problems that the miles of featureless Pacific ocean did.

 

The system was called Uncle Dog/Brother Agate. As I understand it, Uncle Dog were signals transmitted from B-29 navigation ship so the Mustangs could find and form up with them, and Brother Agate were signals transmitted from Mount Suribachi so the Mustangs (and B-29s) could find their way home. Uncle Dog transmitted 3 tones. If the pilot was on course, he got a steady tone. If he was off course to the starboard, he got the morse code signal for U, and to the port, D (hence, Uncle Dog). Brother Agate, I think, were the same set of signals, but transmitted on a different channel as not to interfere with Uncle Dog. I don't know enough about WWII aircraft radios and proceedure to say much more with much confidence.

 

Unfortunately I don't know how widespread Uncle Dog was after the war. You can find pictures of post-war Mustangs both with and without it, so I don't think it became a standard feature. 

 

The AN/APS-13 I don't know much about. I've heard it was introduced to the Mustang late 1944 and became standard on new-build D-20s and later, but I'm not 100% on that and I don't know if it was retrofitted to earlier models. The AN/APS-13 was a system that gave warning of a plane approaching from the rear, via a light and a buzzer in the cockpit. I believe it was also installed in RAF Tempests, and it used to be installed in Lancasters under the name 'Monica', until they discovered out that Luftwaffe night fighters were using Monica signals to find the bombers in the dark. Apparently it had a tendency to just be on all the time at low altitudes if the detection range was set to high, due to ground clutter. It also didn't have any sort of IFF function. It would just let the pilot know that something was coming up behind him.

[Josephs_Piano 6,089]

Uncle dog did not require additional antenna - it used the existing  SCR-522 VHF communication set.  See http://www.506thfightergroup.org/vlrhistory.asp