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Author Topic: NR16020 second world flight dorsal V antenna  (Read 33082 times)

Chuck Varney

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Re: NR16020 second world flight dorsal V antenna
« Reply #15 on: January 06, 2011, 03:17:02 PM »

I don't know what the consensus is.  I wasn't aware that there was a discrepancy.   :-\

I'm sorry to hear that.

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I've added your question to the article on "NR16020 Antennas."

Thank you, Marty.

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I've also found that the same article already had Ric's answer to your other question about the feed point.

I didn't ask a feed point question, but I did point out that the way Mike E. described the wire connection to the first dorsal V was not borne out by photographs.

Perhaps I should set questions aside and make a few more comments to the aforementioned article (though I fear I'm driving you nuts).

Refer to this section:

Calculating final length of the dorsal Vee

"There are lots and lots of good photos of the airplane after it left Miami and the insulators on the dorsal vee are easy to see. There are two insulators right up close to the forward mast and others right up close to the attach points on the vertical fins. There are no insulators elsewhere on the wire."


The title leads the reader to think he's going to learn something about how the length of the second flight dorsal antenna was determined. Instead, there's an extract from a discussion where one side said the antenna could have been shortened by inserting insulators in the legs to create inactive portions, and the second side said that photos revealed the installation of no such insulators. While what the second side said is true, they could have added: the antenna configuration in and of itself has a significant weakly active portion, so its effective length is less than the sum of all the wire used to construct it.

You could improve the article by deleting all of the Calculating final length of the dorsal Vee section.

The same goes for the last three sentences in the section before it, Gurr's Modifications. I'm referring specifically to these:

It was a terrible compromise that provided no meaningful capability to transmit on 500 Kcs while greatly complicating the problem of putting out a decent signal on 3105 and 6210. There appears to have been, however, another consequence to lengthening the vee. The new length made an excellent antenna for the unintended harmonic frequencies."

If it can be shown that the WE 13C couldn't be loaded into the new antenna on 3105 kHz and 6210 kHz without modification or great difficulty then retain the first sentence; otherwise, delete it. If it can be shown somehow that the new length was a significantly better radiator of harmonics than the original, then retain the final two sentences--but first you need to know what the two lengths actually were, electrically. Otherwise, delete both of them as well.

Chuck
« Last Edit: January 06, 2011, 06:12:58 PM by Chuck Varney »
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Martin X. Moleski, SJ

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Re: NR16020 second world flight dorsal V antenna
« Reply #16 on: January 06, 2011, 08:46:38 PM »

Perhaps I should set questions aside and make a few more comments to the aforementioned article (though I fear I'm driving you nuts).

Comments and corrections are always welcome.  I'd like the wiki to be as accurate as possible, all things considered.

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Refer to this section:

Calculating final length of the dorsal Vee ...

You could improve the article by deleting all of the Calculating final length of the dorsal Vee section.

OK.

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The same goes for the last three sentences in the section before it, Gurr's Modifications. I'm referring specifically to these:

It was a terrible compromise that provided no meaningful capability to transmit on 500 Kcs while greatly complicating the problem of putting out a decent signal on 3105 and 6210. There appears to have been, however, another consequence to lengthening the vee. The new length made an excellent antenna for the unintended harmonic frequencies."

If it can be shown that the WE 13C couldn't be loaded into the new antenna on 3105 kHz and 6210 kHz without modification or great difficulty then retain the first sentence; otherwise, delete it. If it can be shown somehow that the new length was a significantly better radiator of harmonics than the original, then retain the final two sentences--but first you need to know what the two lengths actually were, electrically. Otherwise, delete both of them as well.

I've temporized here and just added your comments to the article to indicate that there is disagreement.  Ric has worked with Mike Everette and Bob Brandenburg for many years and has, in my view, earned the right to summarize their discussions.  IF there is any validity to the post-loss radio study, which has not yet been published in full, then some oddities in the antenna configuration may have played a role in producing audible transmissions on harmonics of 3105 or 6210 kcs.

The beauty of the wiki is that it is designed to be updated, so if the discussion here produces consensus, I'll keep on revising the relevant articles.

LTM,

           Marty
           TIGHAR #2359A
 
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Ric Gillespie

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Re: NR16020 second world flight dorsal V antenna
« Reply #17 on: January 07, 2011, 05:47:18 AM »

Can you tell me what the current consensus of the TIGHAR Team is regarding the location of the second world flight dorsal mast?

Here are some options that come readily to hand:

They're all wrong.  There is no Sta. 125 or 129 or 129.5.  The mast was located at Sta. 129 5/8. 
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Chuck Varney

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Re: NR16020 second world flight dorsal V antenna
« Reply #18 on: January 07, 2011, 07:30:51 AM »

Can you tell me what the current consensus of the TIGHAR Team is regarding the location of the second world flight dorsal mast?
They're all wrong.  There is no Sta. 125 or 129 or 129.5.  The mast was located at Sta. 129 5/8. 

Thank you very much, Ric. It appears that in one succinct reply you've  provided an answer, a lesson in the use of the term "Station", and an explanation for some of the variability in numbers.

To see if I'm on the right track, let me rephrase the question: What was the distance, in inches, between the Electra's nose and the center of the mast?

I'm interested in both the distance and the source of the information, if you have that at hand.

Chuck
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Ric Gillespie

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Re: NR16020 second world flight dorsal V antenna
« Reply #19 on: January 07, 2011, 08:07:40 AM »

What was the distance, in inches, between the Electra's nose and the center of the mast?

Lockheed assigned stations numbers based on the number of inches measured aft from the tip of the nose.  Only places where there was a circumferential internal structure (formers and bulkheads) were given a station number.  Sta. 129 5/8 was a fuselage former located 129 5/8 inches back from the tip of the nose.  The position of the exact center of the mast depends on exactly where the mast was installed.  The Harney drawing is based on the available photographs and shows the mast mounted a few inches forward of the double rivet line that marks the station. So, I was wrong and I was right and I was wrong. Technically there is no "Sta. 125" but the center of the mast appears to have been - near as dammit - 125 inches aft from the tip of the nose.

I'm interested in both the distance and the source of the information, if you have that at hand.

The position of the antenna mast was derived from numerous photos of the aircraft.  The information about stations on the Lockheed Model 10 is in "Catalog of Parts - Lockheed 'Electra' - Lockheed Aircraft Corporation".
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Chuck Varney

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Re: NR16020 second world flight dorsal V antenna
« Reply #20 on: January 07, 2011, 08:51:16 AM »

What was the distance, in inches, between the Electra's nose and the center of the mast?

. . .  Only places where there was a circumferential internal structure (formers and bulkheads) were given a station number.  Sta. 129 5/8 was a fuselage former located 129 5/8 inches back from the tip of the nose.  . . . The Harney drawing is based on the available photographs and shows the mast mounted a few inches forward of the double rivet line that marks the station.  . .  the center of the mast appears to have been . . . 125 inches aft from the tip of the nose.

Excellent! Thank you, Ric.

I'm interested in both the distance and the source of the information, if you have that at hand.

The position of the antenna mast was derived from numerous photos of the aircraft.  The information about stations on the Lockheed Model 10 is in "Catalog of Parts - Lockheed 'Electra' - Lockheed Aircraft Corporation".

Again, thank you.

Chuck
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Chuck Varney

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Re: NR16020 second world flight dorsal V antenna
« Reply #21 on: January 10, 2011, 09:26:35 AM »


I closed Reply #3 in this thread with: ". . .the dorsal V as used on AE's Electra cannot be computer-modeled simply as a horizontal V with the source positioned in one leg of the V. Doing that defines a totally different antenna."

Bob Brandenburg's papers, and forum posts between 1999 and 2009, are quiet on this point, but there are a number of hints in them that he did model the dorsal antenna as a V with the source in one leg.

Did he?

Chuck Varney
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Ric Gillespie

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Re: NR16020 second world flight dorsal V antenna
« Reply #22 on: January 10, 2011, 09:31:25 AM »

Bob Brandenburg's papers, and forum posts between 1999 and 2009, are quiet on this point, but there are a number of hints in them that he did model the dorsal antenna as a V with the source in one leg.

Did he?

I'll ask him.
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Bob Brandenburg

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Re: NR16020 second world flight dorsal V antenna
« Reply #23 on: January 10, 2011, 11:35:01 AM »

Chuck,

I modeled the dorsal antenna as it existed, not as a variant of any generic antenna.   The model uses the entire feed wire, including the run from the transmitter to the fuselage penetration point.   The Electra installation had three insulators, one at the apex support point and one each at the tail fin suspension points. 

The antenna model also includes the airframe, using a wire frame model -- comprising about 1,000 segments -- built in 4NEC2.

All dimensions were taken from the Harney drawings.

The antenna gain values are dBi.

Bob
 
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ken jay brookner

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Re: NR16020 second world flight dorsal V antenna
« Reply #24 on: January 10, 2011, 01:33:27 PM »

Thanks, Bob.

kenb
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Chuck Varney

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Re: NR16020 second world flight dorsal V antenna
« Reply #25 on: January 10, 2011, 02:38:47 PM »

Bob,

Thank you for taking time out from your current project to answer my question about modeling (and Ken's about dB's).

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The model uses the entire feed wire, including the run from the transmitter to the fuselage penetration point.   . . . The antenna model also includes the airframe, using a wire frame model -- comprising about 1,000 segments -- built in 4NEC2.

That marks a significant change from the way you appeared to perceive the antenna and model it a decade ago.

Does your wire frame model comprise about 1,000 segments, or about 1,000 wires? I ask because my own 84-wire minimalist wire frame model is divided into thousands of segments, the number depending upon, and increasing with, frequency.

And I know you intended to say The Electra installation had six insulators, a pair at the apex support point and at each tail fin suspension point.   

Chuck Varney
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Bob Brandenburg

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Re: NR16020 second world flight dorsal V antenna
« Reply #26 on: January 11, 2011, 11:23:14 AM »


Chuck,

Yes, there has been a significant change since a decade ago.   In those days, I was using NEC4WIN95, which is based on MiniNEC-3.   Although NEC2 gave better results with wires close to ground, its card-format input scheme and lack of a convenient data editing feature made it unwieldy for quick turnaround modeling, and its antenna gain output was not directly usable in ICEPAC.  I switched to 4NEC2, published about 6 years ago, because it added a 3-D graphical user interface and a spreadsheet geometry editor to NEC2, and generates 3-D antenna gain tables for direct use in ICEPAC.  I mentioned the transition to 4NEC2 in my 2006 paper "Harmony and Power".

The wire frame model comprises 1069 wires which, at 3105 kHz, happens to be the number of segments.   Of course, as you noted, the number of segments increases with frequency.

As for insulators, my intention was merely to convey that there were insulators at those three locations, the point being that the wire section aft of the wire junction on the starboard side was not inactive.


Bob

 
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Chuck Varney

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Re: NR16020 second world flight dorsal V antenna
« Reply #27 on: January 11, 2011, 05:59:43 PM »


Thank you, Bob.

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I mentioned the transition to 4NEC2 in my 2006 paper "Harmony and Power".

I noted the change in modeling software, but from a 2007 forum post it appeared that you retained the method used originally with NEC4WIN95, and described in 2000. Specifically,

With 4NEC2, 28 Apr 2007 (13:25:40):

". . .1).   You need the details of the 3-dimensional antenna configuration:  segment lengths and distances from the fuselage (ground).  You can get these by careful measurements on scale drawings of the Electra, and from photographs of the Electra interior.  . . ."

and earlier with NEC4WIN95, 2 Nov 2000 (20:09:30 EST):

". . .The antenna model I use (see the 8th Edition) does a nice job of computing the 3-dimensional gain pattern for any antenna.  The model does, however, assume a flat ground plane.  To accommodate the model, I measured (using TIGHAR scale drawings) the 3-D distance from the antenna wire to the closest point on the fuselage at 2-foot intervals along the longitudinal axis of the airplane and computed the root-mean-square value over all distances, which I then used as antenna virtual height over a plane ground in the model. . . ."

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The wire frame model comprises 1069 wires which, at 3105 kHz, happens to be the number of segments. 

What a project that must have been. I'd love to see what it looks like. Can you tell me what your model predicts for antenna input impedances at 3105 kHz and 6210 kHz in freespace?

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As for insulators, my intention was merely to convey that there were insulators at those three locations, the point being that the wire section aft of the wire junction on the starboard side was not inactive.

Thanks for clarifying that, as I missed the intended point altogether. As you say, the aft section of the starboard leg was not inactive, but the average current magnitudes in the forward section were enough greater (more than 3 times at 3105 kHz and 7 times at 6210 kHz in one of my models) that one can see how the practical result of it might give birth to the length rule of thumb I mentioned in reply #12. (Modeling the antenna with and without the aft starboard section in a few examples showed that removal of the aft section made the reactive component of the input impedance more capacitive and increased the resistance.)

Chuck Varney
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Bob Brandenburg

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Re: NR16020 second world flight dorsal V antenna
« Reply #28 on: January 12, 2011, 10:38:42 AM »

Chuck,

Sorry about the lag in documenting the antenna model evolution.  The good news is that it's stable now.  When time permits, I'll write up a research paper describing the process and the results. 

The project was far from trivial, but it was greatly facilitated by the excellent tools in 4NEC2, and the detailed dimensions in the Harney drawings.   

The antenna impedance at 3105 kHz is 2.13 - j2.29 ohms.  This is the value obtained with the antenna loading coil set to 19 uH, and a fixed 4,000 pF capacitor in series with the coil per the transmitter specifications. 

The impedance at 6210 kHz is 5.73 - j0.42 ohms, with the loading coil set to 10.6 uH, and a 50 pF series capacitor. 


Bob



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Chuck Varney

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Re: NR16020 second world flight dorsal V antenna
« Reply #29 on: January 12, 2011, 03:36:02 PM »

Thanks, Bob.

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When time permits, I'll write up a research paper describing the process and the results.

I look forward to reading it.

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The antenna impedance at 3105 kHz is 2.13 - j2.29 ohms.  This is the value obtained with the antenna loading coil set to 19 uH, and a fixed 4,000 pF capacitor in series with the coil per the transmitter specifications.

 The impedance at 6210 kHz is 5.73 - j0.42 ohms, with the loading coil set to 10.6 uH, and a 50 pF series capacitor.

Backing out your series components, assuming them lossless and my arithmetic passable, I have your antenna input impedances as:

  2.13 - j 360 ohms at 3105 kHz
    and
  5.73 + j 98.6 ohms at 6210 kHz

Your resistance values are in the range that I'd hoped to see in my attempts, but haven't. For example, the NEC2-computed freespace impedances for my sparse wire frame model (78 12-ga wires for the "Electra" and 6 18-ga wires for the antenna components), are:
 
  0.86 - j 353 ohms at 3105 kHz (0.19 ohms radiation resistance, 0.67 ohms loss resistance)
    and
  2.97 + j 32.5 ohms at 6210 kHz (1.62 ohms radiation resistance, 1.35 ohms loss resistance)

I hope to someday learn what's going on with this.

Chuck
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