Advanced search  
Pages: [1] 2   Go Down

Author Topic: The 3105 Donut  (Read 28836 times)

Mark Petersen

  • T3
  • ***
  • Posts: 125
The 3105 Donut
« on: January 17, 2011, 02:53:39 PM »

I was curious if there is more information about the 3015 Donut (http://tighar.org/TTracks/2008Vol_24/1008.pdf) that Tighar has researched.  In particular I was wondering if the antenna peculiarity described in the link that was responsible for the 80-210 donut around the plane would also apply to line-of-sight.  Also any information on the nature of the antenna peculiarity would be of interest as well. 

As mentioned in the link, this info can be used to establish how close FN and AE came to Howland.  From what I've read and Ric has posted, FN was able to navigate to the LOP with reasonable accuracy (~10 miles), but getting to a specific place on that line (Howland) has a comparatively large degree of error because of the long duration of the flight and the dead reckoning course changes that were done at night (with cloudy weather).  It's not unreasonable to assume then that the accuracy in hitting a specific place on the line is 8-21x greater than the accuracy in getting to the line itself (note that 8-21x corresponds to the 80-210 mile region postulated in the link vs the 10 miles to get to the LOP).  So it certainly seems logical that FN & AE were able to navigate to the LOP SE of Howland.  After failing to find Howland it also seems logical that they would follow the line SE to the only other known landfall.   

But playing "what if" for a moment.  Is it possible that they were somehow able to get closer to Howland and within line of sight?  Given how difficult it would have been to spot Howland when looking into the rising sun (as shown in the Waitt video), it's not surprising that in this scenario they were unable to visually spot Howland, but they would have been in line of sight from a radio propagation perspective.  Does the donut propogation apply to line of sight or was the model constructed assuming that the radio propogation was done "over the horizon"?
Logged

ken jay brookner

  • T1
  • *
  • Posts: 15
Re: The 3105 Donut
« Reply #1 on: January 17, 2011, 06:36:16 PM »

Perhaps someone might point me to how, exactly, this "donut" was calculated.  I've evidently overlooked it trying to find it.  Thanks!

kenb
Logged

Martin X. Moleski, SJ

  • Administrator
  • *
  • Posts: 2951
Re: The 3105 Donut
« Reply #2 on: January 17, 2011, 09:25:27 PM »

Perhaps someone might point me to how, exactly, this "donut" was calculated.  I've evidently overlooked it trying to find it.  Thanks!

Summary with link to original article.
LTM,

           Marty
           TIGHAR #2359A
 
Logged

ken jay brookner

  • T1
  • *
  • Posts: 15
Re: The 3105 Donut
« Reply #3 on: January 18, 2011, 09:11:00 AM »

Many thanks, Marty, but I'm looking for more technical info behind this hypothesis, such as what the antenna anomaly is, how the "donut" was calculated, what software was used, etc.

Any pointers to where I might find it?

Thanks,

kenb
« Last Edit: January 18, 2011, 10:05:34 AM by ken jay brookner »
Logged

Bob Brandenburg

  • TIGHAR member
  • *
  • Posts: 33
Re: The 3105 Donut
« Reply #4 on: January 19, 2011, 11:51:02 AM »

Hi Ken,

I'm busy with another TIGHAR project, but I just happened to check in and saw your question.

The "donut" was computed by the ICEPAC propagation model, using the dorsal antenna gain pattern computed by 4NEC2.   The SNR at the Itasca was computed versus Electra distance in 20-mile increments along the LOP, from 20 miles to 340 miles.   

At short distances, the antenna gain is sharply reduced due to the radiation pattern.   You can visualize the  pattern by cutting an apple in half at its "equator", and letting the distance from the the apple's original center point (which is now in the "equator" plane) to the skin represent the gain.  The dimple where the stem attached to the apple is a good illustration of the antenna's performance at high takeoff angles.   When the Electra was close to Itasca, the SNR was low enough to preclude clear reception.   As the distance increased, the SNR increased, until the distance reached the point where the SNR fell off again due to propagation loss.   Hence the notion of "donut"

It's possible that there was direct path propagation at short distances, due to excitation of the airframe, but ICEPAC only calculates path loss for an ionospheric path.   However, at 1,000 feet altitude (where Earhart said she was flying then), the horizon distance is about 38 miles.  So outside about 40  miles, there wouldn't be any direct path, and skywave would govern. 

Anyway, it's a safe bet that Earhart wasn't within the horizon of Itasca, since the ship would have been visible against the horizon at that distance -- contrary to the common assumption that the visibility of Howland was the controlling factor.   There also seems to be a common assumption that Howland was obscured by the sun.  The only plausible reason for Earhart to be at 1,000 is that there was a cloud deck obscuring the surface from 8,000 feet.   Going down to 1,000 feet put her in the clear, with the cloud deck between her and the sun. but also limited her search horizon.   The Itasca -- even hull down on the horizon -- would be visible against the cloud deck background.  Moreover, Itasca reported making smoke, which would blow along the surface with the wind [coming from about east], and which would be visible as a dark mark on the surface.   I have serious doubts about the feasibility of laying down black smoke for very long, since doing so carried a non-trivial risk of damaging the ship's boiler(s).   But even without the smoke, Earhart and/or Noonan [who had extensive seagoing experience and would know about sighting ships on the horizon] could have seen the Itasca if they were within the visual horizon.

So the donut is our best guess of where the Electra could have been when Itasca was hearing Earhart.

Bob

Bob
Logged

Mark Petersen

  • T3
  • ***
  • Posts: 125
Re: The 3105 Donut
« Reply #5 on: January 19, 2011, 03:44:32 PM »

Hi Bob,

Thanks for taking the time to write up this very thorough post.  It certainly seems to preclude that a line of sight proximity was ever achieved.  What you also said about it being easier to spot a ship on the horizon is interesting, because in fact, the Waitt video shows exactly this.  It was easier in the video to spot the ship anchored off of Howland, than Howland itself.  I've also wondered about the effectiveness of the black smoke that the Itasca generated, because the Itasca is a small ship, with small boilers, and it seems as though its ability to generate enough smoke to make a difference would be limited.  At any rate, thanks for chiming in and helping the rest of us learn more about your interesting research on the 3105 donut and also your thoughts about AE & FN being able to achieve line-of-sight.

LTM,
  Mark
« Last Edit: January 19, 2011, 04:08:37 PM by moleski »
Logged

ken jay brookner

  • T1
  • *
  • Posts: 15
Re: The 3105 Donut
« Reply #6 on: January 20, 2011, 09:20:01 AM »

Bob,

Thanks for the info.  At some point, when you have time, it would be interesting to see the output of this work posted; e.g., az/el/3D pattern and a pictorial of your Electra/antenna model.

Best,
kenb
Logged

Bob Brandenburg

  • TIGHAR member
  • *
  • Posts: 33
Re: The 3105 Donut
« Reply #7 on: January 21, 2011, 09:20:18 AM »

Hi Ken,

It's on my to-do list.

Best,

Bob
Logged

Christophe Blondel

  • TIGHAR member
  • *
  • Posts: 20
Re: The 3105 Donut
« Reply #8 on: January 23, 2011, 06:55:47 AM »


... the radiation pattern.   You can visualize the  pattern by cutting an apple in half at its "equator", and letting the distance from the the apple's original center point (which is now in the "equator" plane) to the skin represent the gain.  The dimple where the stem attached to the apple is a good illustration of the antenna's performance at high takeoff angles.


OK for the apple model, but I would not assume the apple axis to be vertical. I would rather think the emission diagram of the antenna to have its symmetry axis given by the general direction of the antenna. And the antenna we are speaking about, if it is the wire extending externally above the fuselage, is actually very far from the vertical orientation of an antenna set as a pole on land, much closer to a horizontal position. You can still imagine its emission diagram as a donut, but the donut is not lying flat on the table. It is more like a standing or a rolling donut, the axis of which will vary according to the heading of the plane.

Additional effects probably have to be taken into account (e.g. reflections by the fuselage and the sea surface). The remark does not contradict anyway the idea that AE may not have been heard when she was at her closest position to Howland. Actually, if there is a zero of emission in a direction parallel to the fuselage, we may even think that AE could not be heard as long as she was heading precisely towards Itasca, and became clearly audible only when she turned sidewards. The same dependence of the emission diagram on the fuselage orientation may explain why Betty heard Amelia only at the very last moment (supposing she was listening the days before, was she ?), when the plane had moved sidewards and began slipping to the deep.

May be this is too speculative again, but could antenna specialists tell us at least why this apple-donut would have to stand vertically ?

Note added in the evening : sorry I had not checked for the actual shape of the dorsal vee antenna (cf. http://tighar.org/wiki/Dorsal_Vee). With such a V-shape, especially if fed via one of it side ends (on one of the stabilizers), it is not so clear that one gets a minimum of emission along the forward-backward axis. But I still do not understand how such a horizontal antenna would produce a minimum of emission in the vertical direction and a cylindrically symmetric emission diagram around this vertical axis (hence a range that does not depend on the orientation of the plane). So the question remains : does the donut-calculation actually take the shape and orientation of the antenna into account ?

Christophe Blondel (who is no radio specialist, but tries to put together what he remembers of his old lessons on electromagnetism)
« Last Edit: January 23, 2011, 02:39:22 PM by Christophe Blondel »
Logged

Chuck Varney

  • T2
  • **
  • Posts: 94
Re: The 3105 Donut
« Reply #9 on: January 24, 2011, 08:56:52 AM »


OK for the apple model, but I would not assume the apple axis to be vertical. I would rather think the emission diagram of the antenna to have its symmetry axis given by the general direction of the antenna.

Christophe,

The "apple" axis is vertical--if you model the dorsal V antenna over perfect ground, and if you model it so that the excitation source is not within a leg of the V. You will then see that at 3105 kHz and at 6210 kHz the radiation field of the dorsal V is predominantly vertically polarized. The radiation pattern exhibits a zenith "dimple" similar to that of a vertical monopole, but shallower. The magnitude of the horizontal component of the field increases with frequency and serves to fill in the dimple in the pattern as the frequency is raised. The dimple is nearly nonexistent by 8 MHz. At 10 MHz and higher, the dimple in the pattern is gone and the net polarization of the radiated field is horizontal.

Evidence suggests that TIGHAR researchers Mike Everette, and Bob Brandenburg--like you--viewed the Electra's dorsal V to be a horizontal antenna fed by a single-wire transmission line. A modeling option with this view is to consider the transmission line to be lossless and to put the excitiation source in a leg of the V. If you do this you are modeling a horizontal antenna and will see no dimple in the upper part of the pattern. 

The back story for the 3105 Donut article in the October 2008 issue of TIGHAR Tracks is that the dimple became evident when the antenna modeling software was changed from one based on MININEC3 (NEC4WIN95) to one based on NEC2 (4NEC2).  To see if there was a possibility of a MININEC3-based modeling program failing to show the dimple when properly modeled, I modeled the antenna at 1 foot above perfect ground at 3105 kHz with an interpreted Basic version of MININEC3 (NOSC CODE 822, JCL CHANGE 9, dated 11-26-86).

Here is the result for a vertical slice through the pattern so obtained (ANGLE is elevation angle, in degrees):

ANGLE    VERT (DBI)   HORIZ (DBI)   TOTAL (DBI)

  0              4.74          -120               4.74
 10             4.61            -33.5            4.61
 20             4.21            -27.6            4.21
 30             3.51            -24.3            3.52
 40             2.46            -22.1            2.47
 50               .961          -20.6              .992
 60            -1.18           -19.5           -1.11
 70            -4.36           -18.8           -4.21
 80            -9.72           -18.4           -9.17
 90           -17.9            -18.2         -15.1
100            -9.72          -18.4           -9.17
110            -4.36          -18.8           -4.21
120            -1.18          -19.5           -1.11
130               .961         -20.6             .991
140             2.46           -22.1            2.47
150             3.51           -24.4            3.52
160             4.21           -27.6            4.21
170             4.61           -33.5            4.61
180             4.74          -135              4.74

At 90 degrees the vertical component is down 22.6 dB relative to 0 degrees, and the sum of vertical and horizontal contributions (total) is down 19.8 dB. These values indicate very significant dimples in the vertical and total patterns, and show that failure to see a dimple in the pattern of the dorsal V antenna at 3105 kHz cannot be attributed to using MININEC-based software to model it very close to ground.

Chuck Varney
« Last Edit: September 15, 2011, 02:30:20 PM by Chuck Varney »
Logged

h.a.c. van asten

  • T4
  • ****
  • Posts: 322
Re: The 3105 Donut
« Reply #10 on: May 10, 2011, 08:50:15 AM »

ChVar.  The transmitter PA layout gives the impression to have a pi-filter configuration , this being a low-pass filter there is very low risk of harmonics radiation from the aerial , especially if the circuit tuned for low standing wave ratio which gives at the same time high effectiveness on the fundamental , the antenna length , being part of the phase loop ,  playing no great role for such case.
Logged

Chuck Varney

  • T2
  • **
  • Posts: 94
Re: The 3105 Donut
« Reply #11 on: May 10, 2011, 11:19:40 AM »

ChVar.  The transmitter PA layout gives the impression to have a pi-filter configuration , this being a low-pass filter there is very low risk of harmonics radiation from the aerial, especially if the circuit tuned for low standing wave ratio which gives at the same time high effectiveness on the fundamental , the antenna length , being part of the phase loop ,  playing no great role for such case.

h.a.c. van asten,

I think your comment belongs in a "Could Betty Have Heard. . .?" thread, not this one, but in response to it--and assuming you're referring to the Western Electric 13C transmitter--you have misinterpreted  the schematic. There is no pi network, or other low-pass filter provision, in the transmitter's output circuit.

Chuck
Logged

h.a.c. van asten

  • T4
  • ****
  • Posts: 322
Re: The 3105 Donut
« Reply #12 on: May 10, 2011, 12:50:57 PM »

Ch.Var. I considered to see coil and 2 condensers , but will look sharper next time.
Logged

h.a.c. van asten

  • T4
  • ****
  • Posts: 322
Re: The 3105 Donut
« Reply #13 on: May 12, 2011, 11:21:11 PM »

B.Brdbg. From alt. 1000 ft / 305 m the horizon distance is 38 st.mls / 61 km. At a distance of 16 mls , 26 km (EJN , July 2008) thence , island and ship Itasca were between A/c and horizon. However , for the 16 mls distance the optical angle for  island and ship Itasca was 1 arcmin , which is the minimum resolution for the human eye. At 1912 GMT the crew evidently considered having the island head on below whereas it´s true coordinates were 16 mls on the port bow : for the unarmed eye and against the sun glare the visual range was below limits. When A/c went for repair after the 1st attempt accident , 6 x 30 binoculars were on board , it is not known if these were present on July 2 or , left behind due to weight saving measures.
Logged

Gary LaPook

  • T5
  • *****
  • Posts: 1624
Re: The 3105 Donut
« Reply #14 on: September 15, 2011, 02:02:59 AM »


OK for the apple model, but I would not assume the apple axis to be vertical. I would rather think the emission diagram of the antenna to have its symmetry axis given by the general direction of the antenna.

Christophe,

The "apple" axis is vertical--if you model the dorsal V antenna over perfect ground, and if you model it so that the excitation source is not within a leg of the V. You will then see that at 3105 kHz and at 6210 kHz the radiated pattern of the dorsal V is predominantly vertically polarized. It exhibits a zenith "dimple" similar to that of a vertical monopole, but shallower due to the contribution of a horizontally polarized component. The horizontal component magnitude increases with frequency and serves to fill in the dimple as the frequency is raised. The dimple is nearly nonexistent by 8 MHz. At 10 MHz and higher, the dimple is gone and the net polarization of the pattern is horizontal.

Evidence suggests that TIGHAR researchers Mike Everette, and Bob Brandenburg--like you--viewed the Electra's dorsal V to be a horizontal antenna fed by a single-wire transmission line. A modeling option with this view is to consider the transmission line to be lossless and to put the excitiation source in a leg of the V. If you do this you are modeling a horizontal antenna and will see no dimple in the upper part of the pattern. 

The back story for the 3105 Donut article in the October 2008 issue of TIGHAR Tracks is that the dimple became evident when the antenna modeling software was changed from one based on MININEC3 (NEC4WIN95) to one based on NEC2 (4NEC2).  To see if there was a possibility of a MININEC3-based modeling program failing to show the dimple when properly modeled, I modeled the antenna at 1 foot above perfect ground at 3105 kHz with an interpreted Basic version of MININEC3 (NOSC CODE 822, JCL CHANGE 9, dated 11-26-86).

Here is the result for a vertical slice through the pattern so obtained (ANGLE is elevation angle, in degrees):

ANGLE    VERT (DBI)   HORIZ (DBI)   TOTAL (DBI)

  0              4.74          -120               4.74
 10             4.61            -33.5            4.61
 20             4.21            -27.6            4.21
 30             3.51            -24.3            3.52
 40             2.46            -22.1            2.47
 50               .961          -20.6              .992
 60            -1.18           -19.5           -1.11
 70            -4.36           -18.8           -4.21
 80            -9.72           -18.4           -9.17
 90           -17.9            -18.2         -15.1
100            -9.72          -18.4           -9.17
110            -4.36          -18.8           -4.21
120            -1.18          -19.5           -1.11
130               .961         -20.6             .991
140             2.46           -22.1            2.47
150             3.51           -24.4            3.52
160             4.21           -27.6            4.21
170             4.61           -33.5            4.61
180             4.74          -135              4.74

At 90 degrees the vertical signal is down 22.6 dB relative to 0 degrees, and the sum of vertical and horizontal contributions (total) is down 19.8 dB. These values indicate very significant dimples in the vertical and total patterns, and show that failure to see a dimple in the pattern of the dorsal V antenna at 3105 kHz cannot be attributed to using MININEC-based software to model it very close to ground.

Chuck Varney

-------------------------------

Brandenburg never posted his calculations. Varney states that the vertical signal was down 22.6 db but that is not the angle that is important. Brandenberg claims that the inner diameter of the donut is 80 NM (148 KM) for which the radiation angle was 76.1 degrees. This is based on standard near vertical incidence skywave propagation models. Based on Varney's table, the signal for the inner diameter of the donut would be down only about 13 db (somewhere between the values for 70 and 80 degrees.) If we do the calculation for 50 NM (92.5 KM) we find the radiation angle 81.2 degrees so the signal would be down about 15 db, only 2 db less than the signal at 80 NM. At 40 NM the takeoff angle is 83.0 degrees so the antenna output would be down about 17 db, only about 4 db less than at the donut. For a listener to even notice a difference in signal strength, the signal must change by 3 db so, if the signal could be heard from 80 NM away it should have been heard at 50 NM and it would be only slightly weaker at 40 NM. To provide further perspective on this, since these signals have to travel up in the ionosphere for a little bit over 300 KM and then back down, a bit over 300 KM, the path loss for all of these signals is about 110 db. When you factor in the antenna losses, at 80 NM the signal is down 123 db and at 50 NM it is down 125 db and at 40 NM it is down 127 db, not big differences. Brandenberg states that the direct wave propagation would reach out 40 NM from an altitude of 1,000 feet, (and the plane could have climbed higher if south of Howland where the sky was clear,) so most likely the direct wave would reach out 50 NM so filling in the donut hole and eliminating any gap in the radio reception from Earhart.

gl
« Last Edit: December 11, 2011, 12:54:39 AM by Gary LaPook »
Logged
Pages: [1] 2   Go Up
 

Copyright 2019 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