[Lowfer] Active whip antennas
riese-k3djc at juno.com
riese-k3djc at juno.com
Mon Dec 20 22:15:56 EST 2010
thats right you were the tree guy,, nail at 20 Ft with a wire attached
and through a transformer
to coax,,,, great idea
Bob
On Sun, 19 Dec 2010 20:59:02 -0500 Bill Ashlock <ashlockw at hotmail.com>
writes:
>
> Hi Bob,
>
> In every E-probe experiment I have run relating to tall trees, the
> tree acts as a large high-resistance conductor through a resistance
> of 2K to 5K ohms to ground (the trunk). The E-probe couples nicely
> to tree because of its high input resistance but the 2K to 5K
> reduces the voltage level of the signal (unless the trunk is sawed
> through :) The tree usually offers more signal voltage than a 3ft
> metal rod at near ground levels and you can prove this by touching
> the E-probe to the trunk of the tree and see something like a 6db
> increase in signal voltage. I'm sure there is some height that the
> E-probe can be mounted away from trees that exceeds the E-probe
> signal from a tree but that's often academic because it's most often
> that we have to accept their presence.
>
> This leads me onto my 'tree antenna' soap box. I seldom use E-probes
> because of their IM problems... even the good ones. Instead I shoot
> a line over the top of the tallest tree and pull up a 30 to 50ft
> wire. This connects to a 50 to 5 turn transformer (77 ferrite core)
> at the base of the tree that has the other end of this winding
> connected to a ground stake. A 75 ohm coax connects to the 5 turn
> winding and runs from there to the shack (shield isolated from gnd).
> This is form of 'long wire' antenna but it's the trees conductivity
> that has the most effect over performance. The ground at the base of
> the tree also has a large effect on performance since it is located
> where the signal is received, not inside the typically noisy shack.
> The typical sensitivity of this antenna at 185K is -8db...... which
> is plenty for most good communications receivers like the R-75.
>
> Bill
>
> > To: lowfer at mailman.qth.net
> > Date: Sun, 19 Dec 2010 19:37:56 -0500
> > From: riese-k3djc at juno.com
> > Subject: Re: [Lowfer] Active whip antennas
>
> > Bill
> > did you measure or see any difference if the probe was in a tree
> > which would make the support ?
> > I understand that isnt a good idea but it would be one possibility
> for me
> >
> > Bob K3DJC
> >
> > On Sun, 19 Dec 2010 19:32:28 -0500 Bill Ashlock
> <ashlockw at hotmail.com>
> > writes:
> > >
> > > "I wonder if anyone has tried that experiment at a more open
> site,
> > > perhaps hauling the antenna up a wooden mast that wasn't a
> tree."
> > >
> > > John and all,
> > >
> > > You may remember an experiment quite a few years back where I
> set up
> > > my E-probe and potable SVM in an open field where trees were at
>
> > > least 200 ft away. I raised the probe mounted on a insulated
> pole in
> > > incremental distances and measured the signal output on the SVM
> from
> > > a constant signal source many miles away. Turned out that the
> signal
> > > strength was very close to being proportional to the height of
> the
> > > probe. I was careful to have plenty of coax laying on the ground
> at
> > > all probe heights so that the capacity of the shield to ground
> did
> > > not vary in any significant degree and was considered very large
> in
> > > comparison to the probe's input capacity to gnd.
> > >
> > > Bill
> > >
> > >
> > >
> > > > Date: Sun, 19 Dec 2010 18:43:45 -0500
> > > > From: w1tag at charter.net
> > > > To: lowfer at mailman.qth.net
> > > > Subject: Re: [Lowfer] Active whip antennas
> > > >
> > > > > No the output of the preamp will be higher due to the fact
> the
> > > antenna is
> > > > > higher up in the air and in the clear compared to being at
> > > ground level
> > > > > and surrounded by lossy obstructions like vegetation and
> trees,
> > > plus being
> > > > > further away from house wiring and AC noise. I have proved
> this
> > > myself by
> > > > > hoisting an active whip up into a high tree branch and
> observing
> > > the change
> > > > > in the signal to noise ratio.
> > > >
> > > > I wonder if anyone has tried that experiment at a more open
> site,
> > >
> > > > perhaps hauling the antenna up a wooden mast that wasn't a
> tree.
> > > >
> > > > John A.
> > > >
> ______________________________________________________________
> > > > Lowfer mailing list
> > > > Home: http://mailman.qth.net/mailman/listinfo/lowfer
> > > > Help: http://mailman.qth.net/mmfaq.htm
> > > > Post: mailto:Lowfer at mailman.qth.net
> > > >
> > > > This list hosted by: http://www.qsl.net
> > > > Please help support this email list:
> > > http://www.qsl.net/donate.html
> > >
> > > ______________________________________________________________
> > > Lowfer mailing list
> > > Home: http://mailman.qth.net/mailman/listinfo/lowfer
> > > Help: http://mailman.qth.net/mmfaq.htm
> > > Post: mailto:Lowfer at mailman.qth.net
> > >
> > > This list hosted by: http://www.qsl.net
> > > Please help support this email list:
> http://www.qsl.net/donate.html
> > >
> > >
> >
> > ____________________________________________________________
> > How to Fall Asleep?
> > Cambridge Researchers have developed an all natural sleep aid just
> for you.
> > http://thirdpartyoffers.juno.com/TGL3141/4d0ea5cd5b676df5a9m03vuc
> > ______________________________________________________________
> > Lowfer mailing list
> > Home: http://mailman.qth.net/mailman/listinfo/lowfer
> > Help: http://mailman.qth.net/mmfaq.htm
> > Post: mailto:Lowfer at mailman.qth.net
> >
> > This list hosted by: http://www.qsl.net
> > Please help support this email list:
> http://www.qsl.net/donate.html
>
> ______________________________________________________________
> Lowfer mailing list
> Home: http://mailman.qth.net/mailman/listinfo/lowfer
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Lowfer at mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>
>
____________________________________________________________
Globe Life Insurance
$1* Buys $50,000 Life Insurance. Adults or Children. No Medical Exam.
http://thirdpartyoffers.juno.com/TGL3141/4d101e4d32c2ee3af5m03vuc
More information about the Lowfer
mailing list