Advanced search  
Pages: 1 [2] 3 4 ... 10
 11 
 on: August 08, 2018, 10:33:58 AM 
Started by Matt Revington - Last post by Matt Revington
An article about Tom King’s new book “Amelia Earhart Unrescued,”

https://www.pressdemocrat.com/lifestyle/8565065-181/petaluma-raised-archaeologist-writes-about-amelia

I have not read this but it sounds interesting.

 12 
 on: August 07, 2018, 06:54:40 AM 
Started by Ric Gillespie - Last post by Ric Gillespie

4NEC2 can easily model a wire antenna, and that is what it is used for most. But I'm not sure how well it can model the curved metal structure of the aircraft, wings, and tail as more than a few 2D flat planes. I also believe it can't model the variable resistivity and height (tides) of the water under the aircraft. All of these factors may affect the antenna pattern.

Some quick inquiries on improved antenna modeling might be worth TIGHAR checking into.  Especially given the TIGHAR understand of the tides and the radio transmissions since 2003.

A quick online search doesn't turn up anything moire recent than 4NEC2.
Excerpting Bob Brandenburg from another discussion:
"4NEC2 is such a great tool -- it does the segmentation and field addition/subtraction. It's also important to carefully consider the effect of the antenna being close to ground  -- ground in this case being the fuselage.  The "2" in 4NEC2 means the second version of NEC.  The first version assumed the antenna was high enough that ground proximity was not a factor.  Version 2 considers the effect of the antenna being very close to ground.  BTW, there are two other versions: V3 which considers antennas lying on ground, and V4 which considers antenna buried in ground."

 13 
 on: August 06, 2018, 06:42:32 PM 
Started by Ric Gillespie - Last post by James Champion
Quote
Bob Brandenburg created the propagation model for the plane's dorsal vee antenna in 2003.

The files indicate the V antenna was modeled with 4NEC2. This is a free antenna modeling program that models everything as 2D segments. Also, antenna modeling programs have come a long way since 2003.

4NEC2 can easily model a wire antenna, and that is what it is used for most. But I'm not sure how well it can model the curved metal structure of the aircraft, wings, and tail as more than a few 2D flat planes. I also believe it can't model the variable resistivity and height (tides) of the water under the aircraft. All of these factors may affect the antenna pattern.

Some quick inquiries on improved antenna modeling might be worth TIGHAR checking into.  Especially given the TIGHAR understand of the tides and the radio transmissions since 2003.

 14 
 on: August 06, 2018, 01:39:03 PM 
Started by Ric Gillespie - Last post by Friend Weller
Thanks Ric and Bob!  That answered my wonderings about the possibility of any directional wave propagation with regard to the dorsal vee antenna and the aircraft acting as the ground plane.  Being able to see the vertical component of the transmitted wave at 3105 (plus the harmonics) was helpful. 

 15 
 on: August 06, 2018, 12:37:00 PM 
Started by Ric Gillespie - Last post by Ric Gillespie
For those who prefer pictures to pdfs...

BTW, that "dimple" in the top of the 3105 pattern is what caused the "3205 Donut."

 16 
 on: August 06, 2018, 12:16:39 PM 
Started by Ric Gillespie - Last post by Ric Gillespie
Bob Brandenburg has provided the attached propagation models.

"Attached are 4NEC2 output plots showing the pattern for 3105, 6210, 15525, and 24840.  I can't find a plot for 12420 in my files, but that would be midway between 6210 and 15525.  The 3105 pattern is like a round apple, with the stem "dimple" at the top.  That general pattern continues as frequency increases, until at 24840, it gets "squashed" to one side.  The 6210 and 15525 plots show a vertical slice through the pattern, to show the interior. 

The "PB" suffix means the pattern was computed for phosphor-bronze wire, which was typically used for aircraft antennas.  Phosphor-bronze wire resistance is higher than copper, and the model takes the difference into account.   

The antenna patterns are oriented with respect to aircraft heading, i.e relative bearing 000 is dead ahead.  The model runs assume the plane was parked heading north."

 

 17 
 on: August 06, 2018, 10:08:36 AM 
Started by Ric Gillespie - Last post by Ric Gillespie
I think Ted is asking if a contour profile has been created for the dorsal vee antenna on the Electra.

This is way beyond my pay grade but isn't that what I posted?

 18 
 on: August 06, 2018, 08:13:12 AM 
Started by Ric Gillespie - Last post by Friend Weller
I think Ted is asking if a contour profile has been created for the dorsal vee antenna on the Electra.  Bear with me on this for a moment....

Below are two screensnaps of antenna patterns.  The first is for a directional AM array.  It shows major lobes oriented to the north-east and to the south-west with a minor lobe to the north-west and relatively deep nulls separating the power lobes.  Without going into the details of how this array is fed, the orientation and spacing of the towers, the power ratios, and the phase angle, we can see there is pattern where receivers (which are not in the nearfield) distantly to the north-east and south-west would have a better chance of hearing that signal.  True, this is not the same as the Electra's setup but again, bear with me for just a little longer....

The second shows a non-directional contour for a low-power FM signal transmitting using a folded dipole antenna.  In theory omnidirectional, this signal is shaped by the terrain in the immediate vicinity.  This dipole is closer in construction to the Electra's antenna than a simple vertical radiator.  (And yes, Niku is essentially flat so there would be no terrain shaping of the signal.) 

Though neither of these examples are the same as the dorsal vee antenna on the Electra, I too wonder if the orientation of the aircraft would have any bearing on signal propagation and therefore, signal reception.   Given the "donut" in the signal contour which has been previously modeled, was there additionally any phase cancellation due to the off-center feed point of the antenna along with the characteristics of a vee antenna design which could have created a better chance of reception for those listening in certain directions from the aircraft? 

Might this have bearing on why the Itasca, though closer (yes - skywave versus ground wave, the harmonics of an unfiltered output circuit, etc.), could only hear a carrier at times while Betty and others heard much more?  I'm sure Bob Brandenburg could weigh in on this with much more detail.

(I hope I made sense....)

 19 
 on: August 06, 2018, 06:42:11 AM 
Started by Ric Gillespie - Last post by Ric Gillespie
So far, it seems odd that all the harmonic receptions (except Australia) fall in the Latitude range of 20 to 45 degrees N.

Where else could they fall?  That latitude range encompasses North America. That's where the English-speaking people with radios lived.

If the antennae propagation pattern shows a stronger signal at a right angle to the island’s center line, I think there would be a strong argument supporting the hypothesis that AE did land on the island facing 317 degrees N , the only flat SW shore line.

I don't understand how the island's geographic orientation could in any way effect the plane's radio transmissions.

   Also, right engine would be up-shore.

Why would that make any difference?

Please provide the site’s location of the antennae details.

There is no site with the antenna details. Bob Brandenburg created the propagation model for the plane's dorsal vee antenna in 2003.

 20 
 on: August 05, 2018, 10:21:36 PM 
Started by Ric Gillespie - Last post by Ted G Campbell
Thanks Ric.

What I am looking at, is there a correlation between the “harmonic” receptions and the Lockheed’s antennae propagation pattern.

So far, it seems odd that all the harmonic receptions (except Australia) fall in the Latitude range of 20 to 45 degrees N.  Australia is 30 degrees S.

If the antennae propagation pattern shows a stronger signal at a right angle to the island’s center line, I think there would be a strong argument supporting the hypothesis that AE did land on the island facing 317 degrees N , the only flat SW shore line.   Also, right engine would be up-shore.

Please provide the site’s location of the antennae details.

Ted Campbell

Pages: 1 [2] 3 4 ... 10
Copyright 2018 by TIGHAR, a non-profit foundation. No portion of the TIGHAR Website may be reproduced by xerographic, photographic, digital or any other means for any purpose. No portion of the TIGHAR Website may be stored in a retrieval system, copied, transmitted or transferred in any form or by any means, whether electronic, mechanical, digital, photographic, magnetic or otherwise, for any purpose without the express, written permission of TIGHAR. All rights reserved.

Contact us at: info@tighar.org • Phone: 610-467-1937 • Membership formwebmaster@tighar.org

Powered by MySQL SMF 2.0.15 | SMF © 2017, Simple Machines Powered by PHP