[TowerTalk] (no subject)

[K7GCO@aol.com]

In a message dated 02.05.00 16:43:02 Pacific Daylight Time, n4kg@juno.com 
writes:
<< 
 IF you ever want to put other antennas on the tower,
 then Phillystran is a good idea.
 
 BTW,  on the high bands, an antenna at 35 to 40 ft
 OFTEN beats higher antennas during the day, even on 20M. 
 
 My TH6 at 80 ft SUCKS on 10M where my lower
 antennas (at 40 and 60 ft) are ALWAYS better.
 
 Remember, NO  SINGLE  ANTENNA  HEIGHT 
 can cover ALL the angles supported by the ionosphere.
 
 The BEST solution is to have high and low antennas.
 
 de Tom  N4KG
  >>
That is basically correct.  I like a 2 element 5 or 6 band quad or a Raibeam 
at say 35' for stateside and some DX where they do a good job.and more 
elements at 75' +.  The Hex Beam does real well at 35' also.  There is a way 
to come close to 2 beams at different heights with 1 antenna.  There is a way 
to feed a quad horizontally or vertically polarized instantly selectable in 
the shack.  Ground Reflection Factors (see ARRL Antenna manuals in 
40's&50's--they don't show them anymore for some reason) for the same height 
show where one polarization has a lobe, the other has a null and visa versa.  
You at least get 2 different angles of radiation.  However the ground 
reflection loses are higher for vertical polarization and the pattern nulls 
tend to fill in.  Even so a different angle at reduced amplitude can still be 
effective.  

Over salt water vertical polarization can be dominant where it skips in.  
W7DND had a vertically polarized 2 element yagi at beach level over a salt 
water inlet pointing east.  With 5 dB gain no one could touch him stateside 
or DX.  It was total domination.  Those who operate over salt water should be 
limited to 100W.  He had other vertically polarized beams on the beach on 
different bands that were dominant also.   
 
There is another problem with vertically polarized beams on a tower.  It's 
equivalent to a very bad case of RF spill over on to the coax shield, mast 
and tower.  Vertical polarization really lights up the tower, boom, decreases 
potential F/B and broadens the angle of radiation.  It can raise levels of RF 
into the shack also often getting into the audio.  There is a way to cool the 
tower with 1/4 wave stubs on the tower at the right spots.  There is another 
way to reduce the amount of RF induced on the tower.  Have the entire quad on 
one side of the tower for one band and another quad for another band on the 
same boom on the other side--both with good F/B.  There is a spacing for 2 
element quads that gives a great null in the back of the quad and it hardly 
sees the tower.  This way with vertical polarization, it can be far more 
effective without excessive interference from the tower when vertically 
polarized.  It also helps in reducing QSB from polarization shift.  With this 
feed system I have I can also select 45 degree polarization left or right and 
turnstile CW or CCW also which really gives some versatility (6 different 
polarizations) for different angles from 1 antenna at any height.  K7GCO

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