David Woolley wrote:
I tried using a BL1 (4:1) with my K2 and KAT2 to allow earth free
operation using an improvised antenna in a first floor (US = second
floor) flat, but I've come to the conclusion that under almost all
circumstances, even though I'm getting reasonable SWRs, most of the
power is going into heating balun.
I'm sure that this is partly through not originally understanding the
limitations of baluns, in particular that they are only really usable on
the equipment side of a balanced antenna coupler that presents the
design impedance to the balun, or an antenna that does this without a
coupler, so don't really make sense when impedance matching is done on
the equipment side of the balun, as in the KAT2.
There is no difference if the balun is on the input or output side of an
unbalanced tuner. See
<http://fermi.la.asu.edu/w9cf/articles/balun/balun.html#SECTION00050000000000000000>
I assume that you are using the balun because the antenna is balanced.
If not, just use the KAT2 directly.
I just recently set up a similar system, a balanced antenna with a radio
that has an unbalanced tuner built in. What I did was measure the r and
x presented by the feedline with an antenna analyzer. It turned out that
on the two bands that I was concerned about, r values were between 15
and 150 ohms. But there was significant reactance (in my case, inductive).
When I tried loading the antenna directly through a 1:1 balun there was
significant heating. And the SWR was very high, making it hard for the
internal tuner to find a match. I then added some capacitors in series
with the feeders to cancel the reactance. I used a compromise value
which did not reduce it to zero on both bands, but made a significant
dent in it.
As a result, it was possible to load the antenna on both bands with no
detectable heating of the balun.
I suggest that you start by determining what you are dealing with by
measuring the r and x. You may be lucky and have a situation that can be
handled without any switching, as I did. Or you may have a super-low
resistance on some bands, large reactances of opposite signs on
different bands, etc. In that case you might be able to improve the
situation by changing the feedline length.
I would not try to fix this by changing the balun. Knowledge is power:
find out what you are trying to match!
--
73,
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco
_______________________________________________
Elecraft mailing list
Post to: [email protected]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com
