If you can put up a 6M yagi *really* high -- the pattern will approach free
space. The nulls
Bill W5WVO notes go away. 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.
- N0JK
> 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.
>
> Bill W5WVO
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