[TowerTalk] [Bulk] Change in Frequency with Height above Ground

[jimlux]

On 5/27/16 1:10 PM, Roger (K8RI) on TT wrote:
> I find that is another one of those, "In general", or "It all depends"
> <:-)
> I have an Aim that is sensitive enough to show feed point changes in Z
> due to the wind blowing trees? Antennas? Feed lines? Combinations? You
> can watch the parameters changing with the wind and even seasons, but I
> am talking about the 2nd or 3rd decimal place.  Changes so minute the
> you, the rig, or the receiving station will never notice.
>
> These are every day occurrences compared to changing height, or a metal
> boom of variable length on a boom truck, or crane. It would be
> interesting to watch all the parameters change as the antenna is raised
> and then the boom truck, or crane retreats.
>

This is one of the big values of modeling: you can model these kinds of 
things and get an idea of the sensitivity.  The exact numbers probably 
won't match the model, but you can see if there's big changes in Z (or 
pattern) for small changes in surroundings.

For dipoles, and even 3 element Yagis, they tend to be pretty 
insensitive to surroundings.  But 5 el high gain, high F/B antennas tend 
to be pretty sensitive to small changes in element position, 
orientation, or stuff near them.