Hi
Just a follow up on the question about replacing the steel wire with copper
wire.
Today we replaced the steel wire with copper wire. Also, a 100pF in the cap
box was replaced with a 150pF adding 50pF. To compensate for this extra
capacity (+23pF) i added some wire to the horisontal part, in order to lower
the center frequence.
What happend was precisly as foreseen by N6RY Terry. When the wire was
replaced with Cu. The SWR droppen to 1:1.0 at it lowest point.
With the added wire, the resonanse ended up 1825 KHz
I also experimented with the Capacitor temperature coefficient. I had the
box in the cooler, and the conklusion is, that it changes 1 pF per deegre
celcius negativily (lower temp higher capacity). So the antenna will "grow"
shorther as temperature lowers.
So thanks a lot for the help, although it was a lot of work today redoing
the antenna it was totally worth it :=)
>From the test on the air this evening, the antenna seems to radiate as
expected, it got some good signal reports from the states and a 559 from
japan :=)
--
Regards OZ1AXG Flam
----- Original Message -----
From: "Terry Conboy" <n6ry@arrl.net>
To: "OZ1AXG Flam" <oz1axg.nospam@dxmail.dk>
Cc: <antennaware@contesting.com>
Sent: Wednesday, September 24, 2008 9:11 PM
Subject: Re: [Antennaware] 160 meter 3/8 wire, steel or copper
>
> Flam,
>
> I modeled this with EZNEC (without the tower) and assumed the 1.5 mm
> diameter stainless steel wire has a resistivity of 7.2 e-7 ohm-m and
> relative permeability of 1.02. I estimated about 20 ohms of ground
> loss resistance. Here's what happens at 1860 kHz:
> Cu G=-0.43 dBi Z=52.6 -j 46.6 SWRmin=1.13 at 1922 kHz BW=97
> kHz (50 ohm SWR 2:1)
> SS G=-1.48 dBi Z=68 -j 36.2 SWRmin=1.44 at 1907 kHz BW=90 kHz
>
> The adjacent tower will modify these values depending on where it is
> resonant, cross section, etc.
>
> With copper, you should get about 1 dB more signal, a better match to
> 50 ohms, and resonance moved up about 15 kHz. Adding another 27 pF
> in parallel (457 pF total) should restore the resonant point.
>
> 73, Terry N6RY
>
>
--------------------------------------------------------------------------------
No virus found in this incoming message.
Checked by AVG - http://www.avg.com
Version: 8.0.169 / Virus Database: 270.7.1/1688 - Release Date: 9/24/2008
6:29 AM
_______________________________________________
Antennaware mailing list
Antennaware@contesting.com
http://lists.contesting.com/mailman/listinfo/antennaware
|