Re: Elecrafts T-1

[Don Wilhelm-3]

Darrell,

In your example, the 160 meter half wave will work FB on 160 meters with a
feedline that is 1/4 wavelength at 160 meters.  For all other ham bands, the
situation is different - the antenna length will still be a multiple of 1/2
wavelentghth, but the feedline will also be a multiple of a half wave, so
the feedpoint impedance will be high.

While you are correct that a balanced tuner designed for high impedance
loads would be the best, easy bandswitching of such tuners is just not
practical, so you must make compromises.  You are no likely to saturate a
balun at QRP levels, so you can make your compromise choices in many ways -
including just using it.  For the easiest implemlementation of a multiband
antenna with minimum problems, center feed the longest antenna that you can
manage - a balanced antenna is always easier to feed without RF-in-the-shack
and other problems that an end fed antenna.  This is not to say end fed
antennas will not work well, but the center fed antenna does present fewer
problems since it is inherently balanced.

The BL1 balun is quite 'husky' and should serve quite well in either
situation as long as the power limitation is not exceded.

73,
Don W3FPR

> -----Original Message-----
>
> On August 8, 2005 07:03 pm, W3FPR - Don Wilhelm wrote:
> > If your antenna is end fed (like the example of an end fed dipole), the
> > impdance at the antenna feedpoint will be high, but if the
> feedline is an
> > odd multiple of a 1/4 wave (elecrtical), the impedance presented to the
> > shack loaction should be low.  At other lengths, the impedance
> at the input
> > to the feedline will be high or low or something in between and
> will depend
> > on the length of the feedline.  Whether it is better to use a
> 1:1 balun or
> > a 4:1 balun depends on the answer to these questions.
>
> So lets take a worst case example of a 160 meter half wave
> antenna, and use it
> on all bands 160 through 10 meters including the WARC bands to
> align with the
> capabilities of the K2/100.
> As the electrical length of the antenna and feedline will vary
> with frequency,
> different bands will have very different characteristics. I
> suspect that on
> some bands this antenna system including the BL1 balun will be
> very efficient
> and will be able to be matched by the KAT100, however I also
> expect that on
> other bands it will be problematic. I would worry that a BL1 balun would
> become quite inefficient at some frequencies. Do I understand
> this correctly?
>
>
>

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[Stuart Rohre]

Another answer for Darrell, is that a balun is designed to see equal antenna
halves either side of it.  (on its balanced side).

There is no advantage to using one on an end fed dipole.

If you were to feed with coax, to an end fed dipole, and that coax is
quarter wave long, you would transform the high impedance of around 3000
ohms at the end of dipole to something lower at the other end of coax.  But,
because the coax is low impedance and the dipole end is high, you would have
a lot of feedline loss from The SWR reflections.

That is the reason, low loss (with high SWR) parallel high impedance lines
like ladder line or open wires are used to feed end fed dipoles.  You use a
link at the tuner to couple to such lines.  The tuner has a tank coil and
capacitor to tune it to each band of use.

The link has fewer turns than the LC tank, but can also have a cap for
tuning.

If you had any RF issues on the tuner metal case, you could try a 1:1 cable
choke formed by ferrite beads strung on a short coax, and that would then
couple to the balanced line, if you were not using link coupling to the
radio tuner.  However, use of the link and the isolation it affords, also
reduces the pickup of suburban electrical noise.

Stuart
K5KVH



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[Stuart Rohre]

The L network tuner has one less lossy reactive component, (coil or cap).
It also has an unambiguous tune up for optimum power transfer.  Ie, only one
setting of the variable components gives the lowest loss transfer of power.
In a Tee tuner, there are three adjustable parts, and two settings for each
frequency in many cases of matching.

The L net can be used with a ferrite bead cable choke, to feed parallel
lines, if you float the tuner case above ground.  (If the internal
components have one side grounded to case).

Stuart
K5KVH



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[EricJ-2]

Touch paddle integrated into the KXPD1 paddle.

It's a little rough looking right now, but works so well it will be worth
refining it over the next few weeks.

See the first pictures at:

http://www.ke6us.com/KX1.htm

Eric
KE6US
www.ke6us.com
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