Moderators: richierich, ua900, PanAm_DC10, hOMSaR

 
flyer408
Topic Author
Posts: 24
Joined: Tue Jun 15, 2010 1:12 pm

Boeing 707 non-standard second roof antenna

Tue Aug 03, 2021 7:36 pm

Usually all Boeing 707s were equipped with one roof antenna placed on the forward fuselage - so far, so good:

Image



But this Pan Am Clipper (pic taken in 1975) obviously has got a non-standard second one:

Image



Can anybody please tell me what this one was good for, and if it was installed already before delivery or somewhen later? Thank you!
 
User avatar
fr8mech
Posts: 8320
Joined: Mon Sep 26, 2005 9:00 am

Re: Boeing 707 non-standard second roof antenna

Tue Aug 03, 2021 9:07 pm

Those are VHF antennas. The Global only has 2 VHF systems installed, unless there’s a third antenna obscured by the #3 engine. The Pan Am has 3 systems installed.

When was the third installed? No idea. Back in the day, a third VHF system was probably an option. We didn’t put a third on our DC8’s until the ACARS system was installed.
 
blacksoviet
Posts: 1883
Joined: Thu Apr 21, 2016 10:50 am

Re: Boeing 707 non-standard second roof antenna

Fri Aug 06, 2021 5:59 pm

Could analog television stations be received onboard a private aircraft with one of these antennas?
 
User avatar
fr8mech
Posts: 8320
Joined: Mon Sep 26, 2005 9:00 am

Re: Boeing 707 non-standard second roof antenna

Fri Aug 06, 2021 6:29 pm

blacksoviet wrote:
Could analog television stations be received onboard a private aircraft with one of these antennas?


If I remember my schooling, the VHF TV band was pretty low on the VHF spectrum. So, maybe?

I do know that if the control heads could tune to the FM radio band, you’d be able to listen to that, but the VOR/ILS control heads only went down to 108mhz…voice starts at 118mhz…I think. Been a long time.
 
flyer408
Topic Author
Posts: 24
Joined: Tue Jun 15, 2010 1:12 pm

Re: Boeing 707 non-standard second roof antenna

Fri Aug 06, 2021 7:08 pm

Thank you very much for the explanation. I understand that this antenna could as well be fitted at the bottom of the fuselage?
 
User avatar
DL_Mech
Posts: 2713
Joined: Fri Feb 18, 2000 7:48 am

Re: Boeing 707 non-standard second roof antenna

Fri Aug 06, 2021 7:13 pm

blacksoviet wrote:
Could analog television stations be received onboard a private aircraft with one of these antennas?


FWIW, TWA had a separate TV antenna on the vertical stabilizer for television reception. I found this on accident while searching the manuals of a customer 767-231.

As a passenger, I remember watching local NYC TV on an TWA L-1011 while on delay at LGA.
 
User avatar
fr8mech
Posts: 8320
Joined: Mon Sep 26, 2005 9:00 am

Re: Boeing 707 non-standard second roof antenna

Fri Aug 06, 2021 7:15 pm

flyer408 wrote:
Thank you very much for the explanation. I understand that this antenna could as well be fitted at the bottom of the fuselage?


Yes, you frequently see them on the bottom.

In fact, in both pictures you posted, there are VHF antennas below the R1 door.
 
Max Q
Posts: 9067
Joined: Wed May 09, 2001 12:40 pm

Re: Boeing 707 non-standard second roof antenna

Sat Aug 07, 2021 4:35 am

Often it’s set up to use an upper VHF antenna on the ground and a lower antenna while airborne, controlled through the air / ground switch
 
BoeingGuy
Posts: 6640
Joined: Fri Dec 10, 2010 6:01 pm

Re: Boeing 707 non-standard second roof antenna

Sat Aug 07, 2021 5:19 am

fr8mech wrote:
Those are VHF antennas. The Global only has 2 VHF systems installed, unless there’s a third antenna obscured by the #3 engine. The Pan Am has 3 systems installed.

When was the third installed? No idea. Back in the day, a third VHF system was probably an option. We didn’t put a third on our DC8’s until the ACARS system was installed.


IIRC, a third VHF system was an option in the early days of the non-ER 767s. Three VHF systems eventually became baseline on the 767. AA 767s had the center VHF dedicated to ACARS, with no ability to select voice - again per my hazy memory.
 
User avatar
akoma
Posts: 31
Joined: Sun Jun 18, 2017 12:51 pm

Re: Boeing 707 non-standard second roof antenna

Mon Aug 09, 2021 7:33 pm

Max Q wrote:
Often it’s set up to use an upper VHF antenna on the ground and a lower antenna while airborne, controlled through the air / ground switch

The VHF Comm systems are pretty simple. One single coax cable goes from the back of the VHF transceiver all the way to the antenna. No air/ground antenna switching required.
Usually VHF #1 & #3 (if installed) are connected to the top antennas and VHF #2 goes to the bottom antenna, but this can vary depending on airline requirements & aircraft manufacturer.
 
User avatar
Aaron747
Posts: 16031
Joined: Thu Aug 07, 2003 2:07 am

Re: Boeing 707 non-standard second roof antenna

Tue Aug 10, 2021 11:45 am

flyer408 wrote:
Usually all Boeing 707s were equipped with one roof antenna placed on the forward fuselage - so far, so good:

Image



But this Pan Am Clipper (pic taken in 1975) obviously has got a non-standard second one:

Image


Can anybody please tell me what this one was good for, and if it was installed already before delivery or somewhen later? Thank you!


What’s also cool is many carriers’ domestic versions did not have the HF antenna on the tail.
 
User avatar
akoma
Posts: 31
Joined: Sun Jun 18, 2017 12:51 pm

Re: Boeing 707 non-standard second roof antenna

Tue Aug 10, 2021 4:55 pm

[quote=" What’s also cool is many carriers’ domestic versions did not have the HF antenna on the tail. [/quote]

Where I'm from, the 707s all had 2 HF systems installed, besides 2 VHF comm systems. Some of the 707s were ex Braniff, some ex Qantas, some new.

There was one relatively big lightning arrestor & 2 HF antenna tuner units up at the top of the tail. It was not much fun replacing those items up there, and they did fail quite often.
 
N47
Posts: 115
Joined: Tue Sep 26, 2017 7:38 pm

Re: Boeing 707 non-standard second roof antenna

Fri Aug 13, 2021 4:46 am

fr8mech wrote:
I do know that if the control heads could tune to the FM radio band, you’d be able to listen to that, but the VOR/ILS control heads only went down to 108mhz…voice starts at 118mhz…I think. Been a long time.


If you are low enough and like you said if u can tune it to the station you certinaly can.I know for certain adf receivers can pick up am stations i have seen it first hand although it was during flight tests at about 1,000 ft agl. I believe most FM in the us is between 89-107 MHz just shy of the loc band. In fact, the faa everyonce in a while runs into cases where fm stations bleed over into loc bands and cause interference. Then either the emi is identified and delt with or the loc gets another frequency assignment.

Another difference between voice amd nav are polarization. Voice is vertical, nav (loc/gs) are horizontal. In fact all antennas that stick out close to perpendicular to the aircraft (usually blade antennas) are vertically polarized (vhf voice, dme etc). Flush mounted antennas (gps) tend to be horizontal (yes gps is corcularly polarized but the e-field vectors are in the horizontal).

As for the antenna in the photo: Judging by the size and shape i would say its some sort of vhf comm probably arcas or backup.
 
flyer408
Topic Author
Posts: 24
Joined: Tue Jun 15, 2010 1:12 pm

Re: Boeing 707 non-standard second roof antenna

Fri Aug 20, 2021 7:52 pm

Many thanks for these interesting insights!

Who is online

Users browsing this forum: No registered users and 12 guests

Popular Searches On Airliners.net

Top Photos of Last:   24 Hours  •  48 Hours  •  7 Days  •  30 Days  •  180 Days  •  365 Days  •  All Time

Military Aircraft Every type from fighters to helicopters from air forces around the globe

Classic Airliners Props and jets from the good old days

Flight Decks Views from inside the cockpit

Aircraft Cabins Passenger cabin shots showing seat arrangements as well as cargo aircraft interior

Cargo Aircraft Pictures of great freighter aircraft

Government Aircraft Aircraft flying government officials

Helicopters Our large helicopter section. Both military and civil versions

Blimps / Airships Everything from the Goodyear blimp to the Zeppelin

Night Photos Beautiful shots taken while the sun is below the horizon

Accidents Accident, incident and crash related photos

Air to Air Photos taken by airborne photographers of airborne aircraft

Special Paint Schemes Aircraft painted in beautiful and original liveries

Airport Overviews Airport overviews from the air or ground

Tails and Winglets Tail and Winglet closeups with beautiful airline logos