From: <victor13@online.nl>
To: <rsgb_lf_group@blacksheep.org>
Date: Sat, 6 Feb 2010 20:46:05 +0100
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Subject: LF: RE: active ant on metallic mast
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Re: LF: AW: Re: test signal wantedHello Stefan,Roelof,

for about 4 years now I am using an active whip with good results.The
antenna is placed on a shed about 10 m from the house.I varied the hei=
ght
between 2 m and 9 m.With a height of 2 m(the roof) I had alot of qrm=
 and a
low output,raising it to 5m or higher improved things a lot.Less qrm=
 and
higher output,to prevent im i decreased the size of the whip from 1m=
 to 60
cm.At a height of 7m this gives the besr results.no detectable im from=
 local
mw stations and a good S/N ratio of weak signals.As an experiment I re=
placed
the steel pole for a glassfibre one,this didn't change any thing.This=
 could
be espected because of the coax cable you are always at the same poten=
tial
as with a steel pole.Ofcourse  using a battery and a glassfibre change=
s
things but for me this is not very practical because my whip draws 120=
mA @
28V.
Hope to hear more from your experiments,

73
Victor
PA3FNY
  -----Oorspronkelijk bericht-----
  Van: Stefan Sch=E4fer [mailto:owner-rsgb_lf_group@blacksheep.org]Nam=
ens
Stefan Sch=E4fer
  Verzonden: zaterdag 6 februari 2010 17:47
  Aan: rsgb_lf_group@blacksheep.org
  Onderwerp: LF: active ant on metallic mast


  Hi Roelof, LF,

  Roelof, why do you think that this is the case? Interesting Question=
!
"Won't work" means "Won't work properly" it assume. There will be a si=
gnal
but perhaps it is not optimal. And why could this be the case? If the
application is in a metallic housing that is mounted to a metallic mas=
t, the
capacity of the "ground electrode" against the environment must be ver=
y high
(can be seen as infinite, i assume), compared to the active element (g=
ate of
the FET). Perhaps there will also be a better coupling to qrm sources?=
 I
also have to make some measurements. The antennas we use are comparale=
 i
think. So we could share (all) share our experiences :-)

  A special question comes up when a optic fiber cable is used, since=
 in a
coax application there remains a high C of the ground electrode, even=
 when a
symmetrical transformer is used (since the active element has just a=
 few pF
to the far field). That special question is: What will happen, when th=
e
case/ground electrode becomes small against the active element (e.g.=
 circuit
in SMD, small battery inside)?! Will there be a change in the optimal=
 C of
the active element to the far field? I assume, then, one has to define=
 an
optimal C ratio of both electrodes. Will it behave as a short dipole?=
 And
what about a short vertical (30cm) active antenna that is directly pla=
ced on
the ground with a almost ideal conducting ground plane, e.g. aluminium=
 foil
(out of the household) in a radius of 1m (ignoring the local qrm probl=
em, so
e.g. in your garden, apart from the city)?

  On my new qth i made first steps to receive LF with the active anten=
na
mounted just 2m above ground but hung up on a wet tree. Results were=
 vy bad.
I thought that SNR could be better when increasing the active element=
 since
signals were weak (DCF39 at S7), but it wasn't. The optimal length was=
 still
30cm. That seems not only to be "sufficient" but rather optimal! So le=
ss and
more is worse, unaffected by the hight above gnd?

  I think one has to imagine the E-Field lines that are going through=
 the
ambience. The fieldstrength seems just to be very small in a lossy
environment (on my hill, where no trees can be found, the antenna was=
 also
2m up and DCF39 was S9+20). So hight above ground seems to essencial,=
 even
without local qrm. Each decrease of input signal can be compensated by=
 more
gain but SNR decreases, of course.

  What are your ideas to these thoughts? What do you think will happen=
 if
the ground-electrode-C becomes small against the C of the active eleme=
nt?
What will be the optimum C for both? Will the electrodes have the same
"importance", like as a short dipole? Questions over Questions ;-)=20

  Recently i had the idea to test that with a variable antenna of a /p=
 UKW
radio, perhaps two for each electrode. That will be interesting to pla=
y with
;-)

  73!! Stefan/DK7FC


----------------------------------------------------------------------=
------
--
  Von: owner-rsgb_lf_group@blacksheep.org im Auftrag von Roelof Bakker
  Gesendet: Sa 06.02.2010 13:53
  An: rsgb_lf_group@blacksheep.org
  Betreff: Re: LF: AW: Re: test signal wanted


  Hello Stefan,

  Probably a bit late, bit I have been told that an active whip won't=
 work=20
  well on a metalic mast.
  I never tried it myself (still on the to do list) due to lack of a=
=20
  suitable mast.

  73,
  Roelof, pa0rdt



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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML dir=3Dltr><HEAD><TITLE>Re: LF: AW: Re: test signal wanted</TITLE=
>
<META http-equiv=3DContent-Type content=3D"text/html; charset=3Diso-88=
59-1">
<META content=3D"MSHTML 6.00.6000.16788" name=3DGENERATOR></HEAD>
<BODY>
<DIV><SPAN class=3D314413119-06022010><FONT face=3DArial color=3D#0000=
ff size=3D2>Hello=20
Stefan,Roelof,</FONT></SPAN></DIV>
<DIV><SPAN class=3D314413119-06022010><FONT face=3DArial color=3D#0000=
ff   size=3D2></FONT></SPAN>&nbsp;</DIV>
<DIV><SPAN class=3D314413119-06022010><FONT face=3DArial color=3D#0000=
ff size=3D2>for=20
about 4 years now I am using an active whip with good results.The ante=
nna is=20
placed on a shed about 10 m from the house.I varied the height between=
 2 m and 9=20
m.With a height of 2 m(the roof) I had alot of qrm and a low output,ra=
ising it=20
to 5m or higher improved things a lot.Less qrm and higher output,to pr=
event im i=20
decreased the size of the whip from 1m to 60 cm.At a height of 7m this=
 gives the=20
besr results.no detectable im from local mw stations and a good S/N ra=
tio of=20
weak signals.As an experiment I replaced the steel pole for a glassfib=
re=20
one,this didn't change any thing.This could be espected because of the=
 coax=20
cable you are always at the same potential as with a steel pole.Ofcour=
se&nbsp;=20
using a battery and a glassfibre changes things but for me this is not=
 very=20
practical because my whip draws 120mA @ 28V.</FONT></SPAN></DIV>
<DIV><SPAN class=3D314413119-06022010><FONT face=3DArial color=3D#0000=
ff size=3D2>Hope=20
to hear more from your experiments,</FONT></SPAN></DIV>
<DIV><SPAN class=3D314413119-06022010><FONT face=3DArial color=3D#0000=
ff   size=3D2></FONT></SPAN>&nbsp;</DIV>
<DIV><SPAN class=3D314413119-06022010><FONT face=3DArial color=3D#0000=
ff   size=3D2>73</FONT></SPAN></DIV>
<DIV><SPAN class=3D314413119-06022010><FONT face=3DArial color=3D#0000=
ff   size=3D2>Victor</FONT></SPAN></DIV>
<DIV><SPAN class=3D314413119-06022010><FONT face=3DArial color=3D#0000=
ff   size=3D2>PA3FNY</FONT></SPAN></DIV>
<BLOCKQUOTE dir=3Dltr style=3D"MARGIN-RIGHT: 0px">
  <DIV class=3DOutlookMessageHeader dir=3Dltr align=3Dleft><FONT face=
=3DTahoma     size=3D2>-----Oorspronkelijk bericht-----<BR><B>Van:</B>=
 Stefan Sch=E4fer=20
  [mailto:owner-rsgb_lf_group@blacksheep.org]<B>Namens </B>Stefan=20
  Sch=E4fer<BR><B>Verzonden:</B> zaterdag 6 februari 2010 17:47<BR><B>=
Aan:</B>=20
  rsgb_lf_group@blacksheep.org<BR><B>Onderwerp:</B> LF: active ant on=
 metallic=20
  mast<BR><BR></FONT></DIV>
  <DIV id=3DidOWAReplyText11395 dir=3Dltr>
  <DIV dir=3Dltr><FONT face=3DArial color=3D#000000 size=3D2>Hi Roelof=
, LF,</FONT></DIV>
  <DIV dir=3Dltr><FONT face=3DArial size=3D2></FONT>&nbsp;</DIV>
  <DIV dir=3Dltr><FONT face=3DArial size=3D2>Roelof, why do you think=
 that this is the=20
  case? Interesting Question! "Won't work" means "Won't work properly"=
 it=20
  assume. There will be a signal but perhaps it is not optimal. And wh=
y could=20
  this be the case? If the application is in a metallic housing that=
 is mounted=20
  to a metallic mast, the capacity of the "ground electrode" against=
 the=20
  environment must be very high (can be seen as infinite, i assume),=
 compared to=20
  the active element (gate of the FET). Perhaps there will also be a=
 better=20
  coupling to qrm sources? I also have to make some measurements. The=
 antennas=20
  we use are comparale i think. So we could share (all) share our expe=
riences=20
  :-)</FONT></DIV>
  <DIV dir=3Dltr><FONT face=3DArial size=3D2></FONT>&nbsp;</DIV>
  <DIV dir=3Dltr><FONT face=3DArial size=3D2>A special question comes=
 up when a optic=20
  fiber cable is used, since in a coax application there remains a hig=
h C of the=20
  ground electrode, even when a symmetrical transformer is used (since=
 the=20
  active element has just a few pF to the far field). That special que=
stion is:=20
  What will happen, when the case/ground electrode&nbsp;becomes small=
 against=20
  the active element (e.g. circuit in SMD, small battery inside)?! Wil=
l there be=20
  a change in the optimal C of the active element to the far field? I=
 assume,=20
  then, one has to define an optimal C ratio of both electrodes. Will=
 it behave=20
  as a short dipole? And what about a short vertical (30cm) active ant=
enna that=20
  is directly placed on the ground with a almost ideal conducting grou=
nd plane,=20
  e.g. aluminium foil (out of the household) in a radius of 1m (ignori=
ng the=20
  local qrm problem, so e.g. in your garden, apart from the city)?</FO=
NT></DIV>
  <DIV dir=3Dltr><FONT face=3DArial size=3D2></FONT>&nbsp;</DIV>
  <DIV dir=3Dltr><FONT face=3DArial size=3D2>On my new qth i made firs=
t steps to=20
  receive LF with the active antenna mounted just 2m above ground but=
 hung up on=20
  a wet tree. Results were vy bad. I thought that SNR could be better=
 when=20
  increasing the active element since signals were weak (DCF39 at S7),=
 but it=20
  wasn't. The optimal length was still 30cm. That seems not only to be=
=20
  "sufficient" but rather optimal! So less and more is worse, unaffect=
ed by the=20
  hight above gnd?</FONT></DIV>
  <DIV dir=3Dltr><FONT face=3DArial size=3D2></FONT>&nbsp;</DIV>
  <DIV dir=3Dltr><FONT face=3DArial size=3D2>I think one has to imagin=
e the E-Field=20
  lines that are going through the ambience. The fieldstrength seems=
 just to be=20
  very small in a lossy environment (on my hill, where no trees can be=
 found,=20
  the antenna was also 2m up and DCF39 was S9+20). So hight above grou=
nd seems=20
  to essencial, even without local qrm. Each decrease of input signal=
 can be=20
  compensated by more gain but SNR decreases, of course.</FONT></DIV>
  <DIV dir=3Dltr><FONT face=3DArial size=3D2></FONT>&nbsp;</DIV>
  <DIV dir=3Dltr><FONT face=3DArial size=3D2>What are your ideas to th=
ese thoughts?=20
  What do you think will happen if the ground-electrode-C becomes smal=
l against=20
  the C of the active element? What will be the optimum C for both? Wi=
ll the=20
  electrodes have the same "importance", like as a short dipole? Quest=
ions over=20
  Questions ;-) </FONT></DIV>
  <DIV dir=3Dltr><FONT face=3DArial size=3D2></FONT>&nbsp;</DIV>
  <DIV dir=3Dltr><FONT face=3DArial size=3D2>Recently i had the idea=
 to test that with=20
  a variable antenna of a /p UKW radio, perhaps two for each electrode=
. That=20
  will be interesting to play with ;-)</FONT></DIV>
  <DIV dir=3Dltr><FONT face=3DArial size=3D2></FONT>&nbsp;</DIV>
  <DIV dir=3Dltr><FONT face=3DArial size=3D2>73!! Stefan/DK7FC</FONT><=
/DIV></DIV>
  <DIV dir=3Dltr><BR>
  <HR tabIndex=3D-1>
  <FONT face=3DTahoma size=3D2><B>Von:</B> owner-rsgb_lf_group@blacksh=
eep.org im=20
  Auftrag von Roelof Bakker<BR><B>Gesendet:</B> Sa 06.02.2010=20
  13:53<BR><B>An:</B> rsgb_lf_group@blacksheep.org<BR><B>Betreff:</B>=
 Re: LF:=20
  AW: Re: test signal wanted<BR></FONT><BR></DIV>
  <DIV>
  <P><FONT size=3D2>Hello Stefan,<BR><BR>Probably a bit late, bit I ha=
ve been told=20
  that an active whip won't work&nbsp;<BR>well on a metalic mast.<BR>I=
 never=20
  tried it myself (still on the to do list) due to lack of a&nbsp;<BR>=
suitable=20
  mast.<BR><BR>73,<BR>Roelof,=20
pa0rdt<BR><BR></FONT></P></DIV></BLOCKQUOTE></BODY></HTML>

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