-=> On 07-19-97  12:44, Fred Mckenzie said to Ivy Iverson,<=-
-=>"About Multiband Antennas...,"<=-
-=> In a message dated 07-12-97 IVY IVERSON wrote to JEFF EDMONSON:
 
Hi, Fred;
 
 II> Remember, the majority of the radiation from a transmitting antenna
 II> is at the highest-voltage point, in other words, the unfed end(s).
 
 FM> I wish Wayne was here to tackle this one.  As I recall from my
 FM> Antennas class almost 30 years ago, current is what causes radiation. 
 
I shall date myself here... I predate you by a couple of years...  The FCC
1st Phone license class I took back in '64, (and classes and reading
since), tells me that the high-voltage part, (the end), of an antenna is
where most of the radiation comes from.  Of course, the more physical
antenna you have, (IOW not loading coils/capacitors), the more radiation
you get.  Example: A base-loaded, electrical 1/4 wave antenna will tend to
outperform a center-loaded one, all else being equal, but the full 1/4
wave version will outperform both.  Of course when you go to an electrical
5/8 wave, you can base or center load, so all bets are off.   :-}
 
 FM> Signal strength at a distance from a wire antenna, is related to the
 FM> integral (summation) of the differential current flowing in the wire,
 FM> taking distance and angle (relative phase) into consideration.
 FM> Approximately two thirds of the radiation comes from the central
 FM> third of a dipole.  An end-loaded dipole shortened as much as two
 FM> thirds, may be within a couple dBs of a half-wave dipole.  The
 
...AH, but 3 dB is 50% power!   :-[
 
 FM> "Inverted Vee" dipole is based on the idea that it is best to have the
 FM> high current portion of the antenna (center) higher than the low
 FM> current portion (ends), if you can't have the whole antenna high.
 FM> 73, Fred, K4DII
 
I learned that the inverted Vee was more a case of space and money saving
than a radiation advantage.  After all, a Vee, like a level dipole,
requires (at least) two high supports, while an inverted Vee requires only
one.
 
There are two waves radiated from an antenna: The E (Electrical) field and
the H (Magnetic) field.  These are at right angles to each other, the E
being parallel to the orientation of the radiating element, and the H at
right angles to it.  One of these fields, (I have forgotten which), only
travels a few wavelengths before it peters out, and the other is what
gives us the possability of DX communication.
 
Catch you later... Happy Hamming!
   Ivy
 
 
 
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           ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ> Ivy Iverson, KB9QPM <ÄÄÄÄÄÄÄÄÄÄÄÄ¿
           ÀÄ> Ivy's WALL BBS - USA Co-Moderator, INTBBS_WK <ÄÙ
 
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