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Author Topic: Factors influencing radio propagation  (Read 88655 times)

Gary LaPook

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Re: Factors influencing radio propagation
« Reply #45 on: April 16, 2012, 04:01:13 AM »

Too bad Earhart didn't have one of these.



Boy, do these bring back memories.

gl
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William Thaxton

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Re: Factors influencing radio propagation
« Reply #46 on: May 02, 2012, 05:36:39 PM »

Neat little portable!  Unless my memory is playing tricks on me I THINK you can still purchase such a set through marine dealers.  I seem to remember seeing one advertised a few years back and noting how it corresponded to the old RDF (pre-ADF) units on aircraft.

For that matter, I remember the early days of transistor radios (pretty much everything was AM in those days) and their dependence on ferrite rod antennas.  If you understood the concept of "tuning a null" you could work up a pretty good LOP by just rotating the radio and listening to the signal fade and recover.

Neat story, Gary!  It's nice to be reminded of a day and time before we were totally dependant on electronics, satellites, and computer calculated and generated images.

William Thaxton
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Martin X. Moleski, SJ

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Re: Factors influencing radio propagation
« Reply #47 on: May 02, 2012, 10:15:14 PM »

If you understood the concept of "tuning a null" you could work up a pretty good LOP by just rotating the radio and listening to the signal fade and recover.

I've used a boom box in my talks on TIGHAR precisely to demonstrate what "finding a null" means.

Makes me feel good.  I also think it's good for the audience, though no one has ever praised that particular feature of my talks.
LTM,

           Marty
           TIGHAR #2359A
 
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Gary LaPook

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Re: Factors influencing radio propagation
« Reply #48 on: May 02, 2012, 10:41:42 PM »

Chuck,

I'm not qualified to judge your criticisms of Bob's work. I do know that Bob disputes them. ICEPAC is not proprietary to Bob Brandenburg.  The research tools and required information are readily available for you to run your own calculations.   Then you can publish your own analysis of the LOP donut hole and I'm sure Bob will be happy to critique it.
Right, the program is available to everyone but we don't know what assumptions and data that Brandenburg fed into his computer. If he is sure of his assumptions and methodology then he should share them with everybody so the reasonableness of those assumptions can be assessed. If his assumptions are demonstrably  unwarranted then that is all that is needed to disprove his theory. (For example, if Brandenburg was relying on moon bounce propagation and the moon was on the other side of the earth, at the time (known with certainty from the Nautical Almanac), then this is enough to demonstrate that there is something wrong with his results.) Scientists publish their work, including their assumptions and data, so that others can attempt to replicate their results thus adding support to their work. The scientific community is justifiably suspicious of the work of those who don't publish the details of that work.

gl
« Last Edit: May 03, 2012, 03:13:38 AM by Gary LaPook »
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Irvine John Donald

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Re: Factors influencing radio propagation
« Reply #49 on: May 03, 2012, 01:55:47 AM »

Gary, I am very pleased to see that you posted that you are going to the symposium. As Bob Brandenburg will be there I hope that you can get the time to discuss these points with him. It should be a lively discussion but try to keep it at a layman level so the non techies can keep up with the logic.
Respectfully Submitted;

Irv
 
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Jeff Carter

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Re: Factors influencing radio propagation
« Reply #50 on: September 03, 2012, 09:17:02 PM »

I have recently enjoyed tinkering with ICEPAC and ICEAREA. 

Are the ICEPAC antenna data files from Tighar's analysis of the Electra radio transmissions available for download or perhaps with purchase of the Finding Amelia book?

Thanks.
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Martin X. Moleski, SJ

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Re: Factors influencing radio propagation
« Reply #51 on: September 03, 2012, 10:24:22 PM »

Are the ICEPAC antenna data files from Tighar's analysis of the Electra radio transmissions available for download or perhaps with purchase of the Finding Amelia book?

They are not available for download on the site at present.

They're not included with the purchase of the book.

If you enter into direct negotiations with Ric and Bob Brandenburg, and persuade them of your qualifications to do something interesting with the data, they might share it with you.

No harm in asking.   :)
LTM,

           Marty
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C.W. Herndon

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Re: Factors influencing radio propagation
« Reply #52 on: November 07, 2012, 01:51:47 PM »

Here is an interesting document, that I recently found, concerning radio wave propagation. Just thought I would share it with everyone.
Woody (former 3316R)
"the watcher"
 
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Dave Ross Wilkinson

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Re: Factors influencing radio propagation
« Reply #53 on: February 05, 2015, 08:50:12 PM »

If Earhart's strongest signal was heard at Itaska at a very strong, S5, I would think it would be line of sight, within the 42 - 82 nm range suggested, rather than sky wave. 

I suggest this, because a sky wave signal, would have had to travel some 500nm (round trip to the F-layer), and be substantially attenuated.  Also, early in the morning, the D-layer of the ionosphere would be becoming ionized, providing some further attenuation. 

Does this make any sense to anyone?

Dave Wilkinson
 
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Martin X. Moleski, SJ

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Re: Factors influencing radio propagation
« Reply #54 on: February 05, 2015, 08:57:20 PM »

If Earhart's strongest signal was heard at Itaska at a very strong, S5, I would think it would be line of sight, within the 42 - 82 nm range suggested, rather than sky wave. 

I suggest this, because a sky wave signal, would have had to travel some 500nm (round trip to the F-layer), and be substantially attenuated.  Also, early in the morning, the D-layer of the ionosphere would be becoming ionized, providing some further attenuation. 

Does this make any sense to anyone?

I understand the nature of your argument.

I am not in a position to affirm or deny it.  I've never done any calculations of radio propagation myself, just read about such things.
LTM,

           Marty
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Craig Romig

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Re: Factors influencing radio propagation
« Reply #55 on: February 05, 2015, 10:38:41 PM »

Dave I really know very little about radio.  But it makes sense that it was a line of site type of signal. Or line signal and not a bounced signal.

What I do know is in the past I was 60 or so miles south of Kansas City and listened to Chicago AM radio in my truck one night.

The stronger the signal means the closer the transmitter was to receiver.  That's kind of how radio direction finding kind of works.

Someone please correct anything I've said. I'm not even an amateur at radio or signals.
« Last Edit: February 07, 2015, 06:00:45 AM by Martin X. Moleski, SJ »
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Martin X. Moleski, SJ

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Re: Factors influencing radio propagation
« Reply #56 on: February 07, 2015, 06:12:25 AM »

The stronger the signal means the closer the transmitter was to receiver.  That's kind of how radio direction finding kind of works.

Not exactly.

Radio direction finding (RDF) works because you can construct an antenna that is very sensitive when its axis is perpendicular to the transmitting antenna and least sensitive when one end or the other of the antenna is pointed at the transmitter.  By rotating an antenna with these directional qualities (or by flying your aircraft in a circle), you should be able to find a bearing on the transmitter by noticing the WEAKEST reception ("finding a null").  When you find the weakest reception, your antenna is pointing at the source of the transmission--although from a single test, with no other information available, you don't know which end is the significant end of the antenna.  Move forward, repeat the observation, and see where the lines drawn along the axis of the antenna intersect. 




LTM,

           Marty
           TIGHAR #2359A
 
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John Rayfield

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Re: Factors influencing radio propagation
« Reply #57 on: February 15, 2015, 12:13:44 PM »

On the frequencies that were being used by Earhart, the idea of the signal being stronger as the transmitter moved closer to the receiver might only apply to ground wave propagation and not skywave propagation.  If the Itasca was receiving Earhart via skywave propagation, then Earhart could have been moving either closer to, or further away, from the Itasca as the signal increased in strength.  Several factors would influence the range achieved with skywave propagation, including the radio frequency being used, the time of day, the time of year, the 11-year sunspot cycle (the amount of sunspot activity on the sun), the presence (or lack of) solar 'storms', the altitude of the airplane, the design and location of the antenna on the airplane, and effective radiated power (ERP) of the transmitted signal from the airplane.

I've never thought that the Itasca was receiving Earhart, at the strongest point, via ground wave propagation.  Of course, that was the assumption by everyone at that time, and even still today by many people.  But, just because the received signal was very strong was not an 'absolute' indication that she was close to the Itasca.  Based on the fact that nothing was found in searching within the distance from Howland Island, that ground wave propagation would have existed, could indicate that she was much further away from Howland Island than was 'assumed' at the point of strongest received signals.

John Rayfield, Jr.


Dave I really know very little about radio.  But it makes sense that it was a line of site type of signal. Or line signal and not a bounced signal.

What I do know is in the past I was 60 or so miles south of Kansas City and listened to Chicago AM radio in my truck one night.

The stronger the signal means the closer the transmitter was to receiver.  That's kind of how radio direction finding kind of works.

Someone please correct anything I've said. I'm not even an amateur at radio or signals.
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Martin X. Moleski, SJ

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Re: Factors influencing radio propagation
« Reply #58 on: February 15, 2015, 01:58:04 PM »

On the frequencies that were being used by Earhart, the idea of the signal being stronger as the transmitter moved closer to the receiver might only apply to ground wave propagation and not skywave propagation. 

That is a magnificent first post, John.

Very informative!

I've added it to the article in the wiki on "Radio propagation."
LTM,

           Marty
           TIGHAR #2359A
 
« Last Edit: February 15, 2015, 02:03:48 PM by Martin X. Moleski, SJ »
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John Rayfield

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Re: Factors influencing radio propagation
« Reply #59 on: February 15, 2015, 05:25:33 PM »

Thanks.  I've always been interested in the 'mystery' of what happened to Amelia Earhart and Fred Noonan.  I've been a licensed ham operator for a bit over 40 years and have been working in the commercial 2-way communications field for about 37 years.  So, the aspects of her communications has always intrigued me.

As an example of how ground wave and skywave propagation compare in most cases, I'm sitting here listening and visiting with some friends on 14.307 mhz.  The weakest signal is from a station close to me, about 30 miles.  The strongest station is in Oshkosh, WI, about 523 miles north of me.  If I was copying him via ground wave, he would have to be within 10 to 15 miles of me or or closer, with that kind of signal.  Another very strong station is in Florida.  As the sun is setting, more and more of the signals will fade away on this frequency and I'll need to move lower in frequency to be able to hear anyone via skywave propagation.

John Rayfield, Jr.
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