[Milsurplus] Re: Ongoing hf command antenna

[Mike Hanz]

Thank you for that voice of reason, Dave.  Truth is, just about everyone 
has said something correct in this thread, as nothing is black and white 
- even the short fighter antenna radiates /something/ from its 
horizontal element - just not very much.  Marty can delete the rest of 
this because it's from Sandretto [ :-P ], whom I quote because after 
forty years of this stuff I'm tired of writing equations for complex 
geometries, but in my simplistic world, full size antenna range 
measurement trumps mathematical models every time.  In the example I 
mentioned of the fighter antenna with a 15 foot horizontal run and the 4 
foot vertical mast, the horizontally polarized field strength at 5MHz 
was 16% of the vertically polarized component - not a whole lot, but 
hardly zero.  Nature abhors discontinuities.  Sandretto also ends one of 
his sections with an interesting observation - "The airplane antenna can 
be considered a highly efficient device.  The truth of this statement 
was borne out in practice when it was found that some airplanes, 
equipped with antennas having such small effective heights that they 
could hardly be considered much more than unterminated but otherwise 
conventional transmission lines, have radiated usable signals."

I guess it all depends on what your definition of "is" is...heh.

73,
Mike

David Stinson wrote:

>> } End fed wires radiate, whether they're on the top
>> } of an aircraft or not.  A wire is a "capacity hat"
>> } if it's fed near the center so that the fields on
>> } both sides, being of oposite polarity, cancell each
>> } other.  
>
>
> Not so, *assuming* an "electrically short" length of
> about one-tenth wavelength or less.  Be it an inverted "L"
> configuration or a "T," the horizontal element is a non-radiating
> capacitive load- part of the "balanced transmission line"
> we previously discussed.  Where the imbalacing element is
> introduced is irrelevant.
>
> We're tending to mix concepts here, and it's getting us
> at odds while comparing apples to oranges.
> There are big differences between
> a "jeep" antenna of 20 feet at 4 MC,
> a B-29 antenna at 4 MC and
> a "fighter" antenna of 4 feet vertical
> to 12 feet of horizontal top load a 4 MC.
> The jeep and B-29 antennas are significant portions
> of a wavelength, while the the "fighter" antenna is not
> and is in a whole, different "universe" from the
> other two.  It's also a simpler "universe," which
> is why I can understand it and not the others ;-).
> 73 Dave S.
> ______________________________________________________________
> Milsurplus mailing list
> Home: http://mailman.qth.net/mailman/listinfo/milsurplus
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Milsurplus at mailman.qth.net
>