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Constellation Antenna

Old 11th Oct 2017, 03:12
  #21 (permalink)  
 
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Hi i42:

The Lecher Line "size" is determined by the frequency at which it operates (around 200 MHz). In this case, "not large", maybe 18" long. It's two rods of metal in parallel with a shorting link that travels the length of them, powered by a servo motor driving a screw.

The whole thing forms a resonant circuit. in this case strapped to the plate of the transmitter valve. The further out the shorting link, the lower the transmitted frequency.

The Lecher line was mounted in the pressurized case that contained the Rebecca, surrounded by the other electronics. There was a lubricated (Vaseline!) rubber seal at one end. The thing was inflated with a bicycle pump!

The entire contraption was about the size of an office waste basket and twice the length. It was so old, not even Wickipedia has a photo of it: this is the later model!
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Old 11th Oct 2017, 21:48
  #22 (permalink)  
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Back to the Type 308 transmitting antenna.

Peter Clukey from Lockheed Martin confirms that the 649/749 Parts Catalog states that this feature was unique to Qantas aircraft 2562, 2565, 2572 & 2573 (VH-EAA to VH-EAD).

Earlier I searched for this type of antenna on other operators' Connies but couldn't find any. I then widened the search to look for the companion Rebecca antenna on the side of the nose. I found only one, on BOAC Connie G-ANNT. However this aircraft appears not to have any sort of antenna on the tip of the nose.



While we have solved the original Qantas problem, some may feel that we now have a BOAC problem. I'll leave that to our learned colleagues to ponder.
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Old 12th Oct 2017, 00:19
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PS: That's not a small sharks mouth but a reflection of the GPU. Don't you just love polished aluminium?
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Old 12th Oct 2017, 00:35
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Fris B,

Your post is a nice segue into a question I was going to ask.

I’m old enough to have seen dipoles on Vampire T 11 wings at Shawbury in the late 60s. I didn’t know what they were at the time but I now know they were Rebecca receiving aerials.

My question is where were the transmitting aerials?

John,

I had read about the pressurized “can” before you posted. Initially I thought it was pressurized from the aircraft’s systems until I read about the tyre valve. Was there a pressure gauge or did you have to apply a gauge to the valve? What pressure did you pump it up to? I presume the pressurization was to prevent arcing at high-altitude.
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Old 12th Oct 2017, 01:05
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I42

RAAF Neptunes were fitted with a similar system designed to home on downed airmen. This system was known as SARAH (Search And Rescue And Homing) and featured a Yagi type Rebecca receive antenna on each side of the nose and a single transmit antenna on the belly. Unfortunately I don't know what the belly antenna looked like but surely one of us will know.
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Old 12th Oct 2017, 20:44
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I 44 the reb was pumped up on pre-flights with a foot pump to 5 psi. There was a pressure gauge on the pump. Yes It was to stop arcing at altitude.
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Old 13th Oct 2017, 02:01
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Wondering about the purpose of the antenna. Could it have been playing a role in the development of DME, which was invented by Australian James ''Gerry'' Gerrand in the 1944 - 45 period while with the CSIRO? Any ideas? When was DME put in place in Oz, I believe early 1950's?
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Old 13th Oct 2017, 07:50
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megan.

I'm with you. There must be a reason why the 3 antenna's were only fitted to Qantas 749s and from my view DME is a good reason.

As said in an earlier post, I have a friend who was a 749 out stations engineer and I will ask him but he is away right now. I looking fwd to the answer.
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Old 13th Oct 2017, 19:22
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The Hermes had Rebecca early on and I think these are the related antenna. This arrangement can be found on several British operated aircraft of the immediate post war period. Including Yorks, Tudors, Hastings and some BOAC Constellations. The Argonaut appears to have a similar set up to the original post, but I haven't found a good close up picture.
In Larry Milberry's excellent Wilf White propliner collection book there is a photograph of BOAC L749 G-ALAK that also appears to have the nose mounted antenna.

[IMG]HP81-Rebecca by [url=https://www.flickr.com/photos/[email protected]/][/IMG]

Last edited by GAZIN; 13th Oct 2017 at 19:58. Reason: image
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Old 13th Oct 2017, 21:35
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GAZIN

Your Hermes setup looks similar to the Qantas Connies apart from the location of the two transmit antennae. There is another antenna under the nose of the Qantas and BOAC Connies illustrated above and I'm wondering if that precluded installing the Rebecca antennae close by. The Qantas nose location was clearly chosen by Lockheed before the aircraft were delivered in 1947. By 1954 they must have come up with a better idea although it's not clear where the transmit antennae were on BOAC's G-ANNT in 1954 (post #22).
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Old 15th Oct 2017, 04:45
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Fris B.
If you look at your website photos of EAE and EAF which were both ex Air India 649/749s you can see that both aircraft had the similar side antenna but a small arc type nose antenna.

Earlier photos in Air India service had no antennas. So my question still is why Qantas only on the Connies at least?

I found my ex Connie engineer friend and while he remembers the antenna he cant remember what they were.
Wunwing
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Old 15th Oct 2017, 06:43
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Wunwing

Good point. Thus it would appear that the original "nipple" type nose antenna gave way to what you call the arc antenna sometime after 1947 when the Qantas Connies were delivered and 1950/51 when Qantas acquired the two Air India aeroplanes.
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Old 16th Oct 2017, 01:32
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The Qantas nose location was clearly chosen by Lockheed before the aircraft were delivered in 1947
EAB at Burbank prior to delivery.

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