[Elecraft] K2 ATU and 43-ft Vertical

[Edward R Cole]

I am using a top-loaded 43 foot vertical (43x130-foot inverted-L) on 
495.6 KHz (600 meters).  The antenna Z = 0.81 - j681.5 from EzNEC.  I 
built an air coil from #12 thhn copper wire (ordinary solid conductor 
electrical housewire) roughly 10-in diam by 10-inch long 39 turns and 
tapped it about 3/4 for a match.  A tap at 2-1/2 turns matches 
50-ohms coax to the xmtr which is a converted 100w NDB (aviation 
non-directional beacon).
Details at:  http://www.kl7uw.com/600m.htm

The base loading coil is nearly identical in design to the toroidal 
coil of AD5X, linked below.  I do intend to find 160 & 80m tap 
locations for the antenna.

One thing I wanted to share was that I am using 2-foot chicken wire 
as ground radials lying on the ground.  They are obviously short on 
600m (1/4 Wave = 496 feet).  Two radial are 50-foot long and one is 
70-foot long.  I am using the shield of my 1-5/8 inch Heliax hardline 
coax as the fourth radial (it is 120-foot long and has ground rod at each end).

With a modified MFJ-269B, I get a measured Z = 20 + j0; the 50-ohm 
tap sees Z = 63 + j15 for SWR=1.3  antenna efficiency is 4% 
(ERP=4.15w for 100w xmtr output).  With this I have been heard in BC 
over 1300-miles away (not in the prime DX season).

73, Ed - KL7UW
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Message: 15
Date: Sat, 5 Jun 2010 18:26:41 -0500
From: "Bob Naumann" <W5OV at W5OV.COM>
Subject: Re: [Elecraft] K2 ATU and 43-ft Vertical
To: <elecraft at mailman.qth.net>
Message-ID: <017001cb0506$8e203850$aa60a8f0$@COM>
Content-Type: text/plain;       charset="us-ascii"

As Don mentioned, the 2-part article in QST was written by AD5X and can also
be seen here:

http://www.ad5x.com/images/Articles/Match160.pdf

I  built one of these "matching networks" (it's not a tuner) for my 43'
vertical and it works very well on 160, 80 and up. The AD5X matching network
is a very clever design and makes tuning of this short radiator quite easy
as it offsets the huge capacitive reactance of these antennas and even
allows control of the relays right over your feedline. Very slick.

I have a Zero Five vertical and it is made very well, has been up about 3
years and still looks brand new. The only difference is that with the AD5X
matcher I can tune it on 160 and 80 now!

The feedline makes a huge difference primarily due to the loss that will
impact your performance with poor SWR. If you have a lossy feedline (like
RG8X like I used at first) the antenna will appear to match pretty easily.
If you switch (like I did to 1/2" hardline, with its much lower loss) you'll
see the impact of all of that capacitive reactance in making tuning of the
43' antenna very difficult especially on 160 and 80. In fact, I could not
match it at all on 160.

73,

Bob W5OV



73, Ed - KL7UW, WD2XSH/45
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