[Elecraft] Antenna Question

[Charles Greene]

At 10:46 AM 3/24/2002 -0500, John Lucas wrote:
>Now the K2 RF board is comming nicely I need to get the antenna up.
>
>Because of limit space I'm thinking of a 67ft wire from the roof to a tree,
>end feed with about 30ft ladder line comming into the upper floor "shack".
>The ARL handbook indicates a transmatch is needed.  Will the K2 ATU work
>this configuration or do I need a transmatch or both?  If I need the
>transmatch can anyone provide a link to a good design?

--Snip--

John,  I use a W3edp antenna which is 85' of wire with a 17' 
counterpoise.  On 40-15, the 17' counterpoise acts as one side of a open 
wire ladder line and the antenna is a voltage fed antenna, but on 10 and 
80, the antenna is current fed.  So I added a 67' and a 8' counterpoise for 
80 and 10 in parallel with the 17' one.  25' of the wire goes from my 
basement up the side of the second floor, then 60' to a tree.  Where the 
three counterpoise and wire meet, I use a 4:1 balun.  The counterpoise are 
just tacked on the side of the house at about the 3' level, but they can go 
anywhere.  For the balun I have used a Radio Works 2KX current balun or a 
home made current balun consisting of two cores with 13 turns #24 wire each 
biflar wound on FT114-43 cores.  The balun is connected to length of coax 
which then goes to the K2AT.  Works fine 160-10, and the balun does not 
experience excessive loss.  It is operating about 97% efficiency and will 
take 100 watts easily.  The Lengths of wire are such that the SWR at the 
intersection of the antenna and counterpoise is moderately high on all 
bands but not so high that it will damage the balun.  In comparison to 
other antennas, it is about an S unit less than my G5RV at 35' and my 
Hustler 6BTV.  It would work better on the lower bands if it were higher.

A 67' length of wire if fed with open wire line will be a voltage fed 
antenna on 40, 20, and 14, and with an 18' length of open wire line, will 
function as W3EDP antenna on those bands and will probably ok work on 30, 
17, and 12 too if you run a coax from the balun to the K2AT as I did.  You 
might have to try some different lengths of coax, and the coax will have 
moderately high losses.  You will have to do something else on 80 and 
10.  A transmatch has a single ended output so you will need a balun 
somewhere to convert balanced to unbalanced.  There are other types of 
tuners for balanced lines.  An old Johnson Matchbox, if you can pick one up 
at a flea market or on the internet, will tune a wide range of open wire 
impedances.  I have one, but it is not for sale.
73, Chas, W1CG