Just to clarify, using a rule of thumb for stacking VHF/UHF antennas today
is obsolete. Careful modelling must be done and just as Tom points out, you
have to decide what you want to achieve. Some stack for maimum gain,
especially when the array is used for terrestrial (tropo) communication but
when the array is to be used for moonbounce the receive performance (i e
sidelobes/noise pickup) is more important. In most cases max gain and max
receive performance (G/T) do not coincide. And far too many people only
look at f/b as a measure of performance..
Check the G/T table at www.qsl.net/sm2cew and you will find out that even
some antenna manufacturers do not know the optimum stacking distance for
their antennas. Sometimes their suggested stacking distances gives away as
much as 0.5 db which is a lot on EME. It also means putting up a lot more
aluminium than needed in the air for the given gain.
Stacking these days must be done more intelligently than using a rule of
At 04:27 2001-07-28 , you wrote:
>> Tom of course theoretically you are right but in the real life and real
>> practical situations the longer boom you have the wider spacing for
>> maximum gain is needed. (OK various nulls and lobes are comming but....).
>> The discussion - if I understand it well goes for Yagis 0.5 - 1.5 WL !
> I didn't intend to start an argument, just to point out HOW it works.
>Some people like to know how or why something happens, some
>people like to just plod along clueless about how or why things
>work the way they do. If someone has no interest in how it works,
>they should just ignore my post and believe what they like.
>As Mauri points out, that old rule of thumb came from VHF
>antennas and was just a rough rule. It was used because most
>people could not model or calculate optimum distance, and it was
>better than nothing.
>A person who cares about results would model the antenna, not
>use a rule of thumb that may be incorrect. Stacking distance is not
>a function of boom length, it is a function of individual antenna
>patterns and what you want to obtain.
>73, Tom W8JI
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