[TowerTalk] Modeling vs Experimenting

Jim Rhodes jim at rhodesend.net
Thu Sep 12 11:52:08 EDT 2019


Experimenting can give you an antenna that works well, modelling can tell
you why (and even how to improve it).

Jim Rhodes
K0XU

On Thu, Sep 12, 2019, 08:26 Jim Thomson <jim.thom at telus.net> wrote:

>   I use  both  methods.   The problem being in a residential  neigbourhood
> is I am surrounded  by  other  homes, some  with well  grounded wire mesh
> below  stucco  siding,  then the  usual myriad of   neighbours attic +
> house  wiring, copper  plumbing,  then  miles  of  single and  3 phase
> commercial AC  power,  utility poles,
> lamp  standards,  sloping ground, trees,  miles  of  asphalt streets,
> concrete and  asphalt  driveways, hundreds  of metal  cars. Miles of telco
> and  cable  company lines.
> And soon  to be installed   5G  network....  with  ants  mounted every
>  100-300  yards.   One  nearby  home  just installed a ton  of  solar
> panels.   Some homes  are  now installing
> metal roofs.
>
> How  do  you propose how  to  implement HFTA  with  the above ???
>  Loads  of  clay below the pristine lawns too.   Forget the  lousy  ground
> for  a minute, there  is  so much junk
> in  the nearfield, and farfield, how  can  any  software even begin  to
> factor a fraction  of these  extraneous  items?   Same  deal  with  nec2
> and nec4.   Sure, the  say  proposed  yagi,  etc,
> can  be  designed  in  free space.... then  modeled  above sloping... poor
> to average  ground.   Good  luck  with  trying to  correlate  software
> results ...with  reality.      Trying to  compare
> RX  + TX signals  with  nearby hams is an exercise In futility.   One
> night  Im louder, the  next night,  local  buddy  is  louder.  Change
> directions,   and it all changes  again.   Change  bands,
> and its a whole new  ballgame.   Huge  differences  in  band  condx, when
> trying to  compare  with  stations  100  miles north of me.
>
> They  have a sign up at NASA  that sez......  one  test  is  worth a 1000
> opinions.      Want  to see how good  your  CM  choke is, measure the  RF
> current  with a clamp on  RF  ammeter  in  several
> places  on  the  coax,  then again around  the  home and shack, plus
> misc  stuff.   Then  swap  CM chokes, and repeat the  test.  Its a eye
> opener.
>
> Later....  Jim  VE7RF
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