[Milsurplus] RE: Aircraft HF DF capabilities New Question

[Mike Hanz]

B. Smith wrote:

>  Does anyone have any
>  documentation of a DF antenna that was installed in any military or
>  civilian aircraft that had published design specifications that the
>  DF antenna was to be used on any segment of the HF band 2.0 Mcs to
>  18 Mcs. Not special ops but normal line mission aircraft.


Not intentionally, at least by the late 1930s.  Here's a clip from one 
of a series of aircraft radio training manuals originally authored by 
the Naval Research lab in 1936.  This one doesn't have a date, but it 
does mention the RAX as a recently issued receiver so it should be in 
late 1940 or so.

"_Frequency Limitations_"

"The practical frequency range for the aircraft D-F is from about 200 to 
1600 Kc.  Two of the latest models (CXS and DZ), however, have extended 
the range down to 15Kc. with the 1500 Kc. the upper limit.  The upper 
limit of 1500 or 1600 Kc. for the rotating loop D-F is generally 
speaking, established by the considerations that at approximately 1500 
Kc., deviation is usually excessive due to strong reradiation fields, 
and unpredictable because of polarization error, hence the higher 
frequencies become increasingly unreliable.  The lower limit is 
determined mainly by signals available on which to take bearings.  The 
range was extended down to 15Kc. for long range direction finding on 
certain shore stations, the band of 15 to 70 Kc. being especially 
applicable to night direction finding."

"Rotating loops have been designed for use up to 8000 Kc. (Models RDF-1, 
RDF-1B, and DU) which proved impracticable because of the prevalence of 
excessive polarization error, unless the bearing was taken within a few 
miles distance so as to assure the reception of a strong ground wave.  
The use of the frequencies above about 1500 Kc. is, therefore, generally 
unsatisfactory and not recommended."


Despite its somewhat turgid language (commas in unexpected places, and 
only the military ever used the word practicable, AFAIK...heh...) it 
reflects a pretty decent understanding of the limitations of the 
medium.  Note that this is focused on Navy systems, but the Signal Corps 
doesn't appear to have put a lot of effort into researching aircraft 
navigation direction finding before the war.  They must have expected 
the radio range system to magically appear wherever they needed it. :-) 
  (Just kidding, but they do seem to have relied a lot on Bendix 
products with an SCR tag slapped on.)

Best 73,
Mike