+++++++++++++++++
From: "phoon.usinet" <phoon at attglobal.net>
To: <elecraft at mailman.qth.net>
Date: Fri, 7 Feb 2003 11:57:57 -0700
Subject: [Elecraft] Typical dB losses for KAT1

Getting power to the antenna without intervening losses is vital for
portable QRP work, when you don't have much power in the K1 to spare to
begin with.

I lean towards full matching AT THE ANTENNA, and not bothering with the
KAT1.

However, let the debate by list members begin:

Should I take small toroidal resonance coils (mounted roughtly 7' up from
base on a 20 foot Cabella Chineese import fishing pole) to achieve resonance
for 40 and 30M, plus a small toroidal matching coil at the vertical base?
This is my portable vertical backpacking GP.

To achieve resonance for 20 and 15, I use tiny ceramic variable caps, also 7
feet up from the base, instead of coils.  The matching coil at the base is
still needed. Practically no losses are associated with these caps. Work
fine at QRP.

You have to run out of the tent to make a band change.

I'll have anywhere from 12 to 36, 33 foot radials spread out symetrically on
the ground, #26 to #28 wire, fed by 25 feet of 50 ohm coax, so the antenna
is truly unbalanced.  I usually put out 12 or so if I arrive late with
little light left 'till dark, and the rest at my leisure the next morning.

KAT1 description says I'll need a balun to get unbalanced performance,
though.

Or should I build the KAT1 and use it to match from the tent on 30, 40, 20
and 15M (no torroidal resonance, cap resonance, and matching coil required)?

One issue is weight.  Another is convenience (do you want to run out into
the cold at night to change bands?). Still another is dB loss associated
with the KAT1 plus the SWR on the coax feedline to the vertical.

I can compute the loss on the 25 foot feedline due to SWR on the line, but I
don't know the typical dB loss associated with the KAT1, and it is not
specified by Elecraft in the item description.

Suppose I am using the set up described:  20 foot vertical wire on 20 foot
fishing pole mast, 16 33 foot radials on the ground.  What might be the dB
loss associated with the KAT1 tuner for 40, 30, 20 and 15M?

Thanks in advance for estimates and ideas.

Peter Hoon
VE1CHS

--__--__--


Date: Fri, 07 Feb 2003 11:13:10 -0800
From: Wayne Burdick <n6kr at elecraft.com>
Organization: Elecraft
To: "phoon.usinet" <phoon at attglobal.net>
Cc: elecraft at mailman.qth.net
Subject: [Elecraft] Re: Typical dB losses for KAT1

"phoon.usinet" wrote:

> Getting power to the antenna without intervening losses is vital for
> portable QRP work, when you don't have much power in the K1 to spare to
> begin with.
> 
> I lean towards full matching AT THE ANTENNA, and not bothering with the
> KAT1.

Hi Peter,

The KAT1 uses very high-Q components and redundant pairs of relay contacts for
low resistance. Losses should be negligible on all bands with most antennas. Of
course the losses will be higher if the load presents an extremely high SWR on a
particular band, but this can be avoided by using a random wire length that is
not a multiple of a half-wave on any band to be used.

You can eliminate the feedline entirely at these power levels by just connecting
both the radials and the antenna lead directly to the back of the K1. The
antenna wire can then be tossed into a tree, etc. If the SWR is extremely high
and causes problems (such as a "hot" chassis or key), you can usually work
around it by altering the antenna length slightly or by using a balun between
the rig and the antenna/ground system.

I would welcome any actual efficiency loss measurements of the KAT1, but I'm
confident that you'll find its performance to be quite good. You should be able
to carry with you just a few lenghts of wire and perhaps a balun--no feedline or
extra inductors or capacitors--and let the KAT1 do the work. (I hate getting out
of a tent at night!)

73,
Wayne
N6KR

+++++++++++++++++++