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cathay747
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707-400's right wing tip forward-pointing extra antenna probe...anybody know why?

Sat Jul 07, 2018 2:13 pm

Hi all,

Does anybody know why the Rolls Conway-powered 707-400's, and only those models, had the extra forward-pointing antenna boom on the right wing tip? As far as I can find, they all had them...I've seen pics/vids of BOAC, LH, LY, RG, AI birds and they all have it. I've never seen it on any other model of the 707. And I presume it's a HF antenna like the one atop the fin?
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FlyHossD
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Re: 707-400's right wing tip forward-pointing extra antenna probe...anybody know why?

Sat Jul 07, 2018 3:45 pm

Yes, it's a HF antenna. Do a search for "707-400 right wing tip" and you'll get several links/hits.
My statements do not represent my former employer or my current employer and are my opinions only.
 
LH707330
Posts: 1931
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Re: 707-400's right wing tip forward-pointing extra antenna probe...anybody know why?

Sat Jul 07, 2018 5:39 pm

The second HF was an option on the 707s and all 400 operators happened to get them. As far as other carriers, a few of SABENA's 329s had them, as did the first 11 of Qantas' 707-138s. By about 1963 they decided that one was enough and stopped doing it. Here are a few pictures of non-400s with the probe:

Qantas 707-138B:
Image

LH 720B:
Image

Sabena 707-329:
Image

For the 300B, the optional added HF antenna went aft from the wingtip (like many of the early 747s), as seen on the VC-137Cs and a small handful of civilian frames.
 
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cathay747
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Re: 707-400's right wing tip forward-pointing extra antenna probe...anybody know why?

Sun Jul 08, 2018 1:47 pm

LH707330 wrote:
The second HF was an option on the 707s and all 400 operators happened to get them. As far as other carriers, a few of SABENA's 329s had them, as did the first 11 of Qantas' 707-138s. By about 1963 they decided that one was enough and stopped doing it. Here are a few pictures of non-400s with the probe:

Qantas 707-138B:
Image

LH 720B:
Image

Sabena 707-329:
Image

For the 300B, the optional added HF antenna went aft from the wingtip (like many of the early 747s), as seen on the VC-137Cs and a small handful of civilian frames.


Thanks for this. I'd totally forgotten that the QF -138's and the LH 720B's had it; didn't know any SN -300 non-fan-Pratt-powered birds did. And of course the VC-137C's I knew of (total of THREE!), although I've never seen any civilian -300B's/C's with the aft-pointing ones, do you know which airlines?

But my original question still stands...what was the need for a 2nd HF antenna? And since you mention the 747, which I never thought of till reading your post...yeah, all pre-400 series had the 2 aft-pointing HF's. So again, why 2? Was it due to having 2 separate, independent (read: a back-up) HF radio systems and it required a separate antenna for each?
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BravoOne
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Re: 707-400's right wing tip forward-pointing extra antenna probe...anybody know why?

Sun Jul 08, 2018 3:00 pm

The antenna coupler is usually the weakest part of the traditional, single antenna, dual receiver installation. This dual antenna design eliminates some of these pitfalls. Important tp keep in mind that as primitive as HF is, it remains a no go MEL itsm for most long-range oceanic ops. Even in todays CPDLC world it remains the "primary" communications resource.
 
FlyHossD
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Re: 707-400's right wing tip forward-pointing extra antenna probe...anybody know why?

Sun Jul 08, 2018 4:25 pm

cathay747 wrote:
But my original question still stands...what was the need for a 2nd HF antenna? And since you mention the 747, which I never thought of till reading your post...yeah, all pre-400 series had the 2 aft-pointing HF's. So again, why 2? Was it due to having 2 separate, independent (read: a back-up) HF radio systems and it required a separate antenna for each?


BravoOne wrote:
The antenna coupler is usually the weakest part of the traditional, single antenna, dual receiver installation. This dual antenna design eliminates some of these pitfalls. Important tp keep in mind that as primitive as HF is, it remains a no go MEL itsm for most long-range oceanic ops. Even in todays CPDLC world it remains the "primary" communications resource.


BravoOne nailed the answer. The other benefit of having two antennas is that while antenna failures are rare, I can remember that happening once.

Back to BravoOne's reply - at my former operator, we did have occasional HF antenna coupler failures (two HF radios feeding one antenna through a coupler). We learned that turning one of the HF radios to OFF would allow the other HF radio to operate normally - something that would not have been necessary with two antennas (and thus, no coupler). A failed coupler would allow the two HF radios to conflict, thereby giving the appearance that neither HF radio was working.
My statements do not represent my former employer or my current employer and are my opinions only.
 
stratclub
Posts: 292
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Re: 707-400's right wing tip forward-pointing extra antenna probe...anybody know why?

Sun Jul 08, 2018 6:26 pm

A side benefit of two complete systems is that both systems could be used/monitored at the same time even on different frequencies.
 
LH707330
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Re: 707-400's right wing tip forward-pointing extra antenna probe...anybody know why?

Mon Jul 09, 2018 5:39 am

I think it was a reliability thing back in the early 60s, and over time some carriers stopped adding them (like Qantas on their last two) when they realized it was extra weight and drag. Regarding the 300B/C, I recall seeing a picture of one, but now I can't recall.

The 747s before the 400 didn't ALL have them, but many did. At some point later in the production run, they moved it up into the tailfin to save on drag.
 
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cathay747
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Re: 707-400's right wing tip forward-pointing extra antenna probe...anybody know why?

Mon Jul 09, 2018 1:29 pm

THANK YOU all for this info...answers my question and makes sense!

p.s. LH707330 I've never seen a pre-400 747 without them. Not calling you a liar by any means, but if there were any without them, it must have literally been just a handful.
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LH707330
Posts: 1931
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Re: 707-400's right wing tip forward-pointing extra antenna probe...anybody know why?

Mon Jul 09, 2018 7:56 pm

cathay747 wrote:
THANK YOU all for this info...answers my question and makes sense!

p.s. LH707330 I've never seen a pre-400 747 without them. Not calling you a liar by any means, but if there were any without them, it must have literally been just a handful.


Here you go! Bonus: it's got the later CF6-80C2 engines as well.
 
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cathay747
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Re: 707-400's right wing tip forward-pointing extra antenna probe...anybody know why?

Tue Jul 10, 2018 12:57 pm

LH707330 wrote:
cathay747 wrote:
THANK YOU all for this info...answers my question and makes sense!

p.s. LH707330 I've never seen a pre-400 747 without them. Not calling you a liar by any means, but if there were any without them, it must have literally been just a handful.


Here you go! Bonus: it's got the later CF6-80C2 engines as well.


Well to quote grandma from "Titanic"...I'll be goddamned! LOL Thanks, first I've ever seen.
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longhauler
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Re: 707-400's right wing tip forward-pointing extra antenna probe...anybody know why?

Tue Jul 10, 2018 1:14 pm

FlyHossD wrote:
Back to BravoOne's reply - at my former operator, we did have occasional HF antenna coupler failures (two HF radios feeding one antenna through a coupler). We learned that turning one of the HF radios to OFF would allow the other HF radio to operate normally - something that would not have been necessary with two antennas (and thus, no coupler). A failed coupler would allow the two HF radios to conflict, thereby giving the appearance that neither HF radio was working.

I think I am too old, as I remember using HF as the primary and only means of communication when well over the water. I also remember this as being a method of solving an HF "failure". Shutting down one radio, to allow the other to work. While I never experienced it personally, it was always "lore", but never written down.

With today's satellite link using CPDLC and ADS, the "children" of today look at me like I fell off the Ark, when I mention stories like this.

As noted, HF must still be functional even though not being used other than a SELCAL check,
Just because I stopped arguing, doesn't mean I think you are right. It just means I gave up!
 
BravoOne
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Re: 707-400's right wing tip forward-pointing extra antenna probe...anybody know why?

Tue Jul 10, 2018 2:00 pm

Just to add a little more to this conversation, CPDLC (Inmarsat). does not work above say, 82N on a polar routing thus HF, or HFDL needs to be functioning for the "polar crossing" portion of those flights. Now if by chance you are using Iridium for your SATCOM, you are good to go above 82N without the loss of CPDLC. You still need HF as a Primary comm system though. I'm pretty sure the day is just around corner where you will only need a single HF installation if you are CPDLC equipped.
 
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Starlionblue
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Re: 707-400's right wing tip forward-pointing extra antenna probe...anybody know why?

Tue Jul 10, 2018 2:18 pm

longhauler wrote:
FlyHossD wrote:
Back to BravoOne's reply - at my former operator, we did have occasional HF antenna coupler failures (two HF radios feeding one antenna through a coupler). We learned that turning one of the HF radios to OFF would allow the other HF radio to operate normally - something that would not have been necessary with two antennas (and thus, no coupler). A failed coupler would allow the two HF radios to conflict, thereby giving the appearance that neither HF radio was working.

I think I am too old, as I remember using HF as the primary and only means of communication when well over the water. I also remember this as being a method of solving an HF "failure". Shutting down one radio, to allow the other to work. While I never experienced it personally, it was always "lore", but never written down.

With today's satellite link using CPDLC and ADS, the "children" of today look at me like I fell off the Ark, when I mention stories like this.

As noted, HF must still be functional even though not being used other than a SELCAL check,


Ahem. As a newish airline pilot, I frequently use HF only. And yes, we have two HF radios on board our shiny new A350s.

Yes, I'm looking at you, Manila Radio... If Ujung Pandang can do CPDLC in addition to decent VHF, why can't you? But I'm not mad....

Polar and trans-Pacific routes get quite a bit of HF love also. KSHHHHZZHHHHSSSSSHHHHHunreadableKSHHHFKKKSSSHHHSSSHH...
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo

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