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Date: Wed, 27 Nov 2002 15:44:48 +0000
To: elecraft at mailman.qth.net
From: Geoff Cottrell <geoff.cottrell at virgin.net>
Subject: [Elecraft] Re: Elecraft KAT100 question

Vic

About your inverted L for 80 and 160 meters: you wrote:

>   It runs vertically a few feet from
>my tower for about 40 feet, and then about another 120 feet horizontally.  The
>KAT100 matches it on both bands, but of course the SWR on the coax between the
>KAT100 and the antenna is quite high.

I have also been experimenting with a similar antenna concept and 
have tried a few combinations.  This is my experience.

My current 50 ft high 160 m quarter wave (or similar) inverted L 
works fine provided you have a good ground radial system.  I have 
about 40 radials and about 50 sq metres of chicken wire under the 
feed point.  It is fed directly with 50 ohm coax and I get 1.5:1 SWR 
on about 1830 kHz.  Obviously no good for 80m and/or 40m as it 
stands.  So to multi-band:  there are 3 options, I am on number 3 and 
having considerable success with it.

Option 1)  put traps for 40m and 80m in (like the inverted L version 
of the Battle-Creek Special, discussed in ON4UN's book: Low-Band 
DXing).  This ant I had for a year until a few weeks ago and works 
well.  Good SWR on 1830, 3510 and 7010 kHz.  My traps were home made 
made from RG213 on a 6 inch PVC soil pipe former and sealed against 
the elements. The vertical nature of the 80m and 40m parts of the 
antenna mean good DX but poor local work.  I am trying a simple wire 
ant now (no traps) on the grounds that the coaxial cable traps are 
somewhat lossy, particularly at the resonant frequencies, less so on 
160m.  W8JI suggests that trap losses can be reduced by designing 
them to resonate at about 90% of the required frequency or so.  I 
have not tried this.

Option 2) Do as you say and parallel-up the 80m and 160m quarter wave 
ants with a common 50 ohm feed point.  My understanding is that they 
should not interact too much provided the wires are kept about 2 feet 
or more apart. This is particularly important at the high-Z wire 
ends.  It should be possible to add a 40 m wire as well.  I have not 
tried this but some people say it works fine.

Option 3) Stay with the 130 foot wire and operate it on both 80 and 
160!!  How?  I built a simple high-Z voltage feed ATU to feed the 
inv-L on 80m.  This works extremely well both for DX and local qsos. 
Use the 160m ground system at the feed point (yes it helps to have a 
ground).  The advantage of this is that you only have one wire and 
that on 80m you not only use the whole wire but the current maximum 
is high up, with both horizontal and vertical components: good for DX 
and local.  The downside is that you have to perform switching and 
tuning operations to resonate for different parts of the 80m band.  I 
am thinking about a tapped coil and a few relays to do this remotely. 
The 2:1 bandwidth on my system is about 100 kHz, which means 3 to 4 
taps needed to cover the 3.5-4 MHz.  The KAT100 should easily be able 
to deal with this.


Hope this helps

73

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From: "Parker Buckley" <pbuckley at woh.rr.com>
To: <elecraft at mailman.qth.net>, <k4wtf at EnterZone.Net>
Date: Sun, 8 Dec 2002 11:44:22 -0500
Subject: [Elecraft] 160M antenna at WD8JOL

I don't know how to reply in a thread, so if this starts a
new topic, sorry.  Also apologize if we're getting off the
K2 topic.  My 160M antenna is an inverted L, but folded back
on itself in a manner similar to a folded dipole to raise
the input impedance.  This helps when the vertical part is
not too high (40 ft here).  This design is presented in the
books by Orr and Cowan.  One side of the antenna connects to
the coax inner; the other side is connected to ground and
the braid.  Ground here consists of 16 #14 insulated wires
in the sod, average about 30 ft.  Obvious area for
improvement.  I used 450 ohm line for the first 121 ft 3 in,
then 9 ft 11in of single conductor to get the overall length
correct.  This accommodates the .95 vf of the line, cut for
1.84 MHz.  My lengths were off a little from Orr's
guidelines, so I spent some time with an antenna analyzer to
tune.  Several years ago I made one with homebrew open line,
which was less finicky to tune and had wider bandwidth.
Using real open line, you don't reduce to the single line at
the far end, since the vf is almost 1.0.  I think it's a
better way to go.  Happy to provide more details off-line.

Parker WD8JOL

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