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Author Topic: testing AE's radio set up  (Read 8068 times)

Matt Revington

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testing AE's radio set up
« on: April 14, 2023, 06:24:37 AM »

A video about a group ( associated with Nauticos) that assembled a radio set up as close as possible to AE's and did some transmission tests over the Atlantic.  I have only had time to briefly scan the video but would like to hear the opinions of those more familiar with aircraft communications

https://www.youtube.com/watch?v=itdUFTszLhs
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Ric Gillespie

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Re: testing AE's radio set up
« Reply #1 on: April 14, 2023, 08:12:19 AM »

Close only counts in horseshoes and hand grenades, but these guys weren't even close.  Not the same transmitter, not the same aircraft type, and not the same antenna set-up.  All of those things are crucial, but what you can't replicate is the electromagnetic environment on a particular date and place 85 years ago.  Garbage in, garbage out.  Also, the progressive strengths of Earhart's transmissions upon which their reverse engineering is based, were not measurements recorded in the logs. They were, in most cases, subjective recollections made weeks later. Only the two S5 estimates when Earhart was thought to vie closest to Howland were noted in the log.

Historical re-enactments never prove anything.
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Clarence Carlson

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Re: testing AE's radio set up
« Reply #2 on: April 23, 2023, 01:48:38 PM »

I listened all the way through up to the Q & A. Ric summed it up well. Earhart's transmitter was modified in ways that are not well documented. We don't know exactly what modifications were made to radio after the length of the Vee antenna was changed. We do know that there were some problems with modulation in her transmitter, which can't really be replicated. Not mentioned at all is the fact that, except for acknowledging the reception of the letter A on 7500 kHz, Earhart did not appear to receive transmissions from Itasca at any other time. The video did confirm what was known in 1937: 7500 kHz is not a usable frequency for obtaining a minimum with a Bendix loop antenna.

The most critical factor is the condition of the ionosphere on July 2, 1937, which can't be replicated.  As they say, there is no there, there.

Clarence Carlson
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Ric Gillespie

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Re: testing AE's radio set up
« Reply #3 on: April 23, 2023, 03:47:31 PM »

The most critical factor is the condition of the ionosphere on July 2, 1937, which can't be replicated.

It can't be replicated but it can, and has been, defined by Bob Brandenburg using ICEPAC.  See The Radio Riddle

This explanation of ICEPAC is fromThe Post-Loss Radio Signals : Technical Analysis

ICEPAC[1] is the Ionospheric Communications Enhanced Profile Analysis and Circuit prediction program, developed by the Department of Commerce Institute for Telecommunications Science (ITS) at Boulder, Colorado. ICEPAC is a direct descendant of the Ionospheric Communications Analysis Program (IONCAP) and is a product of nearly 60 years of research, by ITS and its predecessors in the U.S. Department of Commerce, in collecting ionospheric data and developing methods for using those data in predicting and analyzing the performance of high-frequency (HF) communications systems which depend on ionospheric propagation. ICEPAC runs with the Windows 98 operating system.

ICEPAC computes HF system performance over a specified path, using a combination of user inputs and the contents of internal data base files. User inputs are: year, month, and day; the hours within the specified day, and the radio frequencies, for which performance results are desired; sunspot number [2]; the geographic coordinates of the transmitter and the receiver; the transmitting and receiving antennas to be used; the input power supplied to the transmitting antenna; and the level of man-made noise at the receiving site. The internal data base files contain: (1) statistical parameters of the time-dependent variations of the ionosphere [3] and of atmospheric noise; and (2) the characteristics of commonly used antennas in terms of antenna gain in one-degree increments of azimuth and elevation, relative to an isotropic [4] antenna.

For each run, ICEPAC gives the great circle azimuth and distance from the transmitter to the receiver, and the reciprocal azimuth from the receiver to the transmitter. Additionally, for each user-specified combination of time of interest and frequency, ICEPAC computes 22 parameter values, any subset of which can be selected for display in a variety of graphic and tabular formats. Signal-to-Noise Ratio (SNR) at the receiver site is the principal ICEPAC output used in this analysis. ICEPAC gives SNR in terms of the median [5], 10th-percentile [6], and 90th percentile [7] values, to quantify the range of statistical uncertainty due to random variations in the ionosphere and in atmospheric noise. Lucas and Haydon [8] provide a detailed mathematical treatment of the methods used in ICEPAC to model those variations.
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