[DX] Yagi height and DX

[n4kg@juno.com]

John, 

You have done amazingly well with an antenna at only 20 ft.
At that height, almost ALL of your energy is being radiated
above 10 degrees and much of it going into outer space
and NOT being reflected back to earth.

At 40 ft, almost all of your energy will be refracted back to
earth.  This height is optimum for daytime operation on
the high bands during higher sunspot activity and still
provides reasonably good coverage at night.  I expect
40 ft would be a BIG improvement over 20 ft.

To cover the really low angles which are more prevalent
at band openings / closings you would need to go even higher.

At 50 ft and above, the pattern in the vertical plane breaks
into multiple lobes will DEEP NULLS in between.

To cover ALL the angles supported by the ionosphere,
I recommend HIGH (60 to 70 ft) and LOW (40 to 50 ft)
antennas.  This is a POWERFUL combination that 
provides both directional and waveangle diversity.

I do NOT like 80 to 100 ft for tribanders since that height
places deep NULLS in the upper range of daytime angles
on 10 and 15M.  At 120 ft, the first lobe gives good coverage
of the lower angles and the second lobe covers the 
upper angles.  A LOW tribander fills in the nulls at the
intermediate angles.

I strongly recommend that you read the ARRL Antenna
Book on Propagation and effect of height.  To optimize
your coverage of ALL the angles and propagation modes
on ALL paths under ALL conditions would take more 
antennas than most of us would install. :-)

Tom  N4KG  RF Engineer / All Band DXer / Contester
	       20 antennas on 7 towers of  40 ft to 130 ft
	       9BDXCC = 2872


On Fri, 12 Apr 2002  John Geiger <johngeig@yahoo.com> writes:

> I am currently using a Cushcraft MA5B mounted on a
> tripod on top of a one story house-approximately 20
> feet off the ground.  This antenna has worked well,
> but I am wondering if I am hitting the performance
> plateau with it.  I have 294 worked, including 4 new
> ones this year-JD1o, PW0T, VP6DI, and XW0X.  
> 
> It seems that I am not hearing so well, though.  Last
> night several 5 land stations reported SV2ASP/A as Q5
> on 20 meter SSB, but I could not hear a thing.  Also
> could not hear VK9L on 15 ssb that other stations were
> putting on the reflector.
> 
> I plan on replacing the MA5B with a full size
> tribander right after the KH1 dxpedition.  WOuld like
> to do it before,but need to make sure I have something
> up for that station.  HERE IS MY QUESTION:  WOuld
> getting a tower and going to 40 feet make a hugh
> difference over 20 feet?  Is it worth the trouble of
> getting a tower and putting it up (do not look forward
> to this).  Will that extra 20 feet allow me to hear
> THAT much better?  
> 
> Figured I would get some profession opinions before
> jumping into anything.  WOuld have to sell some gear
> that I like to get the tower also.
> 
> 73s John NE0P
> 

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