[Elecraft] [K3] KAT3 and 160 with 40m long doublet
WILLIS COOKE
wrcooke at yahoo.com
Sun Jan 2 14:51:18 EST 2011
That is a really tough antenna to match for 160 Stephen. The classic way to use
an 80 meter dipole on 160 is to short the feed line at a ground point and feed
it with the center conductor with the braid to the best counter poise you can
manage. This will make you a T topped Marconi which will probably tune for you.
Willis 'Cookie' Cooke
K5EWJ
________________________________
From: Stephen Prior <sjp at sjprior.fsnet.co.uk>
To: elecraft <elecraft at mailman.qth.net>
Sent: Sun, January 2, 2011 1:31:06 PM
Subject: [Elecraft] [K3] KAT3 and 160 with 40m long doublet
I have only just recently added the KAT3 and I'm very impressed with it, but
given the praise heaped upon it by others I'm slightly surprised that the
best VSWR I can get on 160m is about 8:1. The antenna is approximately a
doublet which is a half wave long on 80m I say 'approximately' as it's
slightly off-centre fed. I have about 7m of 300 ohm slotted down from the
feedpoint and then into a coaxial choke at roof level for the remaining 10m
into the back of the K3. Substituting the straight connection for a 4:1
balun (Guanella) at the transition between the slotted feeder and the coax
helps slightly but not by much.
Unfortunately I don't have a vector analyser, so I have no idea of the
nature of the reactance that the K3 is seeing. However, given the
wavelength involved, I would need to add a very significant length of
coaxial cable if I were to swing the point around the Smith Chart.
I have tried to manually tune the KAT3, but unless I am missing something,
I am am not able to change the L and C values at the same time as
transmitting, so it's a very tedious process.
Tomorrow I may well add some extra wire to hang vertically down from the
ends of the doublet. In the meantime I would be pleased to hear any
comments.
Happy New Year!
73 Stephen, G4SJP
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