[Elecraft] KAT100 and external watt meter question

Fri Jan 31 00:50:01 2003

As Roy Lewallen W7EL of EZNEC "fame" reminds us, power must be
conserved. Power that leaves the transmitter must eventually end up at
the antenna, less what might be lost along the way in a tuner or in
line loss. And, given sensible tuner design and adjustment and
low-loss line suited to high SWR conditions, most of the power that
leaves the transmitter will leave the antenna as radiation, despite a
high SWR on the line.

To put some numbers into the discussion, it turns out that 100 ft of
600-ohm open-wire line terminated in an antenna impedance of 94+j500
ohms (a significantly non-resonant antenna!) on 20 meters will operate
at an SWR of 10:1 and show a total power loss of only 0.38 dB and will
deliver nearly 92% of the applied power. Even at an SWR of 20:1 (load
= 43+j500 ohms), the line loss is only 0.78 dB for an efficiency of
nearly 84%.

Try the same thing with RG-213, though,  and although you will see
about the same SWR  (about  11:1 for the same load Z), the power loss
soars to 10.3 dB and the efficiency drops to only 9.33%. Here a high
SWR is something to be concerned about because of the excessive line
loss it produces in a line unsuited to the application.

The goal of good engineering is to match methods and materials to the
job to be done, and the open-wire line is clearly the better choice.
Note that although the actual SWR is about the same in both cases -
around 11:1 or so  - with a low-loss line, the system operates at
quite acceptable efficiency.

73/72, George
Amateur Radio W5YR -  the Yellow Rose of Texas
In the 57th year and it just keeps getting better!
Fairview, TX 30 mi NE of Dallas in Collin county EM13qe
K2 #489  IC-765 #2349 IC-756 PRO  #2121 IC-756 PRO2 #3235

----- Original Message -----
From: "Stuart Rohre" <[email protected]>
To: "Glenn Maclean" <[email protected]>; <[email protected]>;
"Tom Hammond" <[email protected]>
Sent: Thursday, January 30, 2003 6:22 PM
Subject: Re: [Elecraft] KAT100 and external watt meter question

> ACTUALLY, the antenna performs the same whether or not you have SWR
equal to
> 1:1!
>
> The only difference when not 1:1 impedance relation to the feedline,
is that
> there will be higher line losses.  Pattern, radiation efficiency
etc. are
> not a function of SWR, but of antenna design, height, construction
material
> etc.
>
> The antenna does not care about what line is connected to it, it is
going
> "to do its thing" with whatever power reaches the antenna after
> rereflections.
> 73, Stuart K5KVH
>
>
> _______________________________________________
> Elecraft mailing list: [email protected]
> You must be a list member to post to the list.
> Postings must be plain text (no HTML or attachments).
> See: http://mailman.qth.net/mailman/listinfo/elecraft
> Elecraft Web Page: http://www.elecraft.com