[VHFcontesting] Optimum 6 meter yagi height summary (LONG)

[DAVE CLEMONS]

On June 28 I sent a message to this reflector asking for information
on the optimum 6 meter yagi height.  I thought that others might want
to see the replies I received, so I am including them here.

In the interest of preserving the privacy of the responders, I have
removed names and email addresses.  Each response is separated by a
line of "-" characters.

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There have been several articles written about antenna heights on 6m.
In short, height is dependant on elevation angles of the propagation
mode desired.

15-35 ft is the best for single hop Es and meteor scatter. I operate
at the W0AIH/W0UC contest station and the 8 ele at 40 ft is always
better than the 150 ft stacks and the single 11 ele at 170 ft.

During multi-hop Es I find that the elevation angles are changing a
lot and sometimes a higher antenna will be better but most of the time
I use a lower antenna. The high stacks play nice on this mode because
it captures a bigger swath of the arriving angles.

For aurora, groundwave, and F2 a higher antenna is always better. The
stacks and 11 ele are always better.

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Yes...40 ft. for E's...80 ft. for F2.

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Low antenna height (below 1 wavelength) is best for short single-hop E-skip 
and aurora.  Raising the yagi drops the takeoff angle of the main lobe, 
which is better for groundwave and F2.  Since single-hop E-skip is the 
propagation that will be of greatest help generating a high score, the 
optimum height for 6m contesting seems to be 0.6 wavelengths.  A dipole at 
that height shows a slight peak in gain versus all the other nearby height 
figures (and shows a takeoff angle of 23 degrees).  So use low heights for 
high-angle E-skip contacts, then when the band dies, rely on the horizontal 
polarization to nab the locals.

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For sporadic E, assuming flat land, it appeared that the best compromise 
height was about 50-60 feet.  For tropo, on the other hand, the higher the 
better.  There's a strong argument for having antennas at different heights
for different purposes.

Urban development around the station, sloping ground, etc. will change things,
of course.

Meanwhile, I do most of my contesting as a rover, with a dipole at 12 feet,
which is definitely the wrong height !

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   Yes, you are right.  Very similar to 10m.  I've had too much antenna too 
   high on both 10m and 6m for the closer in openings.  I live in the Seattle
   area of Washington state.  There will be a massive opening on 6m to the 
   northeren part of CA and with the larger ant/array you wind up working 
   stations after everyone else even with high power on your end.

   I think it comes down to what it is you are trying to work.  Very few have
   the capabilities to run several towers with different antenna combinations.

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6m is just like any other band.

http://lists.contesting.com/_vhfcontesting/2001-07/msg00046.html

If you want to work forward scatter on a dead band then you need
as much gain at as low an angle as possible.

For Es and F2 - you can put an antenna a 1.5 wavelengths high
and do really well.

For F2 - again - alot of gain up high can be very good.

Remember - high is a relitive term.  A wavelength on 6m 
is about 20 feet.

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29.4ft...  1.5 wavelengths...

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50-60 feet is a good average height to shoot for. (Wish I could get my 2x5el 
stack that high.) However, sporadic-E can want take-off angles all the way 
from flat (0 degrees) up to around 16 degrees for very short skip. The 
length of the skip depends on the intensity of the cloud's ionization (the 
Es MUF). When the Es MUF is very high and the skip very short, you're much 
better off with a lower antenna (as low as 20 feet), assuming your 
surrounding ground is relatively clear so you can make best possible use of 
the ground bounce gain.

Apart from a low take-off angle (not always what you want, but often) -- The 
other thing that greater antenna height affords you, and a lot of people 
overlook this fact, is that the higher the antenna, the further it is from 
man-made noise sources on the ground. A quieter band is a band where you can 
hear (and work) weaker signals! Noise is also discrimminated against in the 
azimuth plane, so a longer yagi with a narrower beamwidth not only has more 
gain on transmit, but picks up less noise (unless it's pointed right at the 
noise source). That is assuming the long yagi has been computer-modeled 
properly and has minimal side- and back-lobes.

Putting a 6-meter yagi REALLY HIGH (like, over 100 feet) will give you the 
maximum possible signal at the horizon for tropo and bleeding-edge Es and F2 
DX -- but it will also give you lots of ugly NULLS in the elevation pattern 
where your signal can drop by as much as 15-20 dB. So you might be pinning 
somebody's S-meter at 1,450 miles away, but the guy who is 900 miles away 
isn't going to hear you anywhere near that loud, all other things being 
equal. Then you need to go to a lower antenna to cover that nulled take-off 
angle.

As all the 6m Big Guns will tell you, the ideal solution for 6 meters is a 
stacked set of long-boom yagis at various heights from "real low" to "real 
high" that you can switch around either for single use or for use in phased 
combinations. Since most "normal people" can neither afford nor find space 
for an antenna system like that, it all comes down to compromises and 
trade-offs.

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That is entirely in agreement with the calculations I was doing back in
2004. I figured that, from a contest perspective, if limited to a single 
antenna it was probably better to have it a little too high than too low,
since the area on the ground and (typically) the population base of 
potentially workable stations covered by a pattern with good performance at
low elevation angles was more than what was covered at the higher elevation
angles (coverage of which also depended on the much rarer short skip).

Now if I only had a chance to put this into practice !

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If you can put up a 6M yagi *really* high -- the pattern will approach free
space. You will be loud at all E-skip distances and for groundwave.

This situation may occur if one operates portable from a really high peak or 
next to a cliff with a sharp drop off.  Or from a tall building.

If you have the opportunity to operate 6M portable from a high quiet location,
it is amazing how the band sounds.

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Yes!

 Your bottom line was spot on!

"Since most "normal people" can neither afford nor find
space for an antenna system like that, it all comes down to
compromises and trade-offs."

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Dave Clemons

dave at egh.com
EGH
55 Waltham Street
Lexington, MA 02421
Tel (781)861-0670
Fax (781)860-9321
www.egh.com