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What Is That Wire?  
User currently offlineSimongkhon From Sweden, joined Oct 2003, 49 posts, RR: 0
Posted (10 years 10 months 1 week 6 days 2 hours ago) and read 4611 times:

In older pix of 737-100:s and 200:s, u sometime can see some kind of wire mounted between the center top of the fuselage and the tail fin. What is that?


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Photo © F. de Ruiter



And how come the wire isn't there on 737-200:s still operated?



10 replies: All unread, jump to last
 
User currently offlineLeskova From Germany, joined Oct 2003, 6075 posts, RR: 70
Reply 1, posted (10 years 10 months 1 week 6 days 2 hours ago) and read 4549 times:

You can actually still find a lot of 737s around that have that wire - there was at least one thread about that about 1-2 months ago, but since I cannot find that at the moment: if I recall correctly, that wire's an antenna...


Smile - it confuses people!
User currently offlineJwenting From Netherlands, joined Apr 2001, 10213 posts, RR: 19
Reply 2, posted (10 years 10 months 1 week 6 days 2 hours ago) and read 4526 times:

It's a radio antenna for long range radio transmitters.
In these days of satelite radio it's no longer required so most aircraft had the equipment removed.



I wish I were flying
User currently offlineMD11Engineer From Germany, joined Oct 2003, 14127 posts, RR: 62
Reply 3, posted (10 years 10 months 1 week 6 days 2 hours ago) and read 4518 times:

Looks like a HF antenna for short wave transmissions. You only need it if you are out of range of VHF stations, most 737s flying in Europe or North America don´t have HF installed becauseof the good VHF coverage of the countries. You´ll need it if you fly over oceans or lowly poulated areas. Additionaly today they are much smaller and usualy incorporated in the vertical stabilizer or wing tip.

Jan


User currently offline5T6 From United States of America, joined Dec 2003, 283 posts, RR: 0
Reply 4, posted (10 years 10 months 1 week 6 days 2 hours ago) and read 4496 times:

My guess is that it's an HF antenna for comms outside the range of normal VHF radios.

I think that most aircraft now use satellite tranceivers for long-haul communication thus the lack of HF antennas on most planes now. I believe that there's still some HF used for transoceanic flights, though.

Mike



I see my Cats as Companions. My Cats see Me as Furniture!
User currently offlineSimongkhon From Sweden, joined Oct 2003, 49 posts, RR: 0
Reply 5, posted (10 years 10 months 1 week 6 days 2 hours ago) and read 4437 times:

Swift answers  Smile/happy/getting dizzy

Thanx a lot


User currently offlineMr Spaceman From Canada, joined Mar 2001, 2787 posts, RR: 9
Reply 6, posted (10 years 10 months 1 week 6 days ago) and read 4344 times:

Hi guys.

Didn't some older aircraft, such as the DC-3s in the photos below use "long wire" antennas for the radio compass (ADF), or am I confused?

In this photo, you can see 3 wires that are attached to the bottom of the DC-3's pitot tubes. Is it possible that the 2 thin wires (that are obviously in a set together) are for the 2 ADF's in the cockpit? Perhaps the thicker wire (also attached to the pitot tubes), is for a HF antenna.


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Photo © Erik Frikke



In this photo, you can see 2 old radio compasses on the instrument panel directly behind the left side control wheel. They're marked ADF 1 & ADF 2.


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Photo © Thorbjørn Brunander Sund - Birdlike Multimedia



If the 2 thin wires are not used for the 2 ADF's, could the 2 black "pod shaped" antennas on the DC-3's belly (aft of the pitot tubes), be used for them?

Here's a photo showing both the black pods and the set of thin wires.


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Photo © Harald Verch



This DC-3 has a lot of antennas on it. The only one that I'm pretty sure about is the silver metal one that's curved & protruding out of the middle of the nose. It's an ILS receiver antenna ....... I believe. Big grin


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Photo © Anders Presterud



PS, if you click on this DC-3's registration (LN-WND) there's 5 pages of photos of her.

Chris  Smile




"Just a minute while I re-invent myself"
User currently offlineMr Spaceman From Canada, joined Mar 2001, 2787 posts, RR: 9
Reply 7, posted (10 years 10 months 1 week 6 days ago) and read 4332 times:

Hi guys.

I wanted to add these photos too, of DC-3's with the same type of antenna as the 737-1. Other smaller GA aircraft and Bush Planes have them as well (but I didn't want to go to crazy with the pix  Laugh out loud )


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Photo © Jan Lidestrand
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Photo © Dimitris Triadafillou



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Photo © Brenden
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Photo © Tobias Rose



Chris  Smile



"Just a minute while I re-invent myself"
User currently offlineDanman From United Kingdom, joined Jul 2002, 39 posts, RR: 0
Reply 8, posted (10 years 10 months 1 week 5 days 23 hours ago) and read 4307 times:

This opens a whole can of worms however;
The wire on the 737 is the HF antenna. Wire antenna were used on the slower flying a/c types before the more modern suppressed types of antenna came into use. Mention has been made of Satcom, this is available but the bulk of the world's fleet does not yet have it fitted. I am not aware of it's use anywhere for ATC purposes.
To the DC3.
As you may or may not be aware ADF requires two antenna, even in a very modern installation, where they are combined. They are the loop and sense antenna. The loop is housed in the 'pod shaped' housings, the sense antenna is probably the wire, although it could also be something that looks like a towel rail on this generation of aircraft.
On to the antenna on the nose, the pic is not too good but it looks like a glide slope antenna (part of the ILS system) The other part of the ILS system (Localizer) will use the 'cow's horn' antenna on the flight deck roof (probably also used for VOR)
Hope this helps


User currently offlineMr Spaceman From Canada, joined Mar 2001, 2787 posts, RR: 9
Reply 9, posted (10 years 10 months 1 week 5 days 22 hours ago) and read 4281 times:

Hello Danman.

Thank You for your info about the ADF and it's 2 different antennas and for explaining that the "Cow's Horn" antenna on top of the cockpit's roof is for receiving the localizer part of an ILS signal.

Well, I don't know if this will open a whole can of worms, but, it will inform people that if you see an aircraft with a wire running from the tail down to the top of the fuselage, or along the belly (usually on larger, older aircraft), the wire could be part of an ADF's antenna system.

I'm just showing another possibility. Big grin

Here's some better shots of the 2 ILS antennas on the DC-3.


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Photo © Erik Frikke



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Photo © Bernhard Bauske
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Photo © Stefan Kunert



This photo shows the wires under the fuselage better.


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Photo © Erik Frikke



>> I found this link about ADF's. It has good, easy to read info in it.

This is stated in the link ..........

"All ADF systems have two antennas. With the older ADF systems you have two separate antennas. The loop antenna is usually located on the bottom of the aircraft and is a flat antenna. The sense antenna is the long wire that runs normally from the top of the tail to the top of the cabin. This antenna is sometimes located on the bottom of the aircraft, especially on larger aircraft."

http://www.avionicswest.com/adfarticle.htm

Chris  Smile



"Just a minute while I re-invent myself"
User currently offlineHAWK21M From India, joined Jan 2001, 31702 posts, RR: 56
Reply 10, posted (10 years 10 months 1 week 5 days 15 hours ago) and read 4235 times:

HF Antenna fitted on the older B737s.
The later models had the Antenna fitted in the LE of the Vertical Stablizer.
regds
HAWK



Think of the brighter side!
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