[Elecraft] BL2 Question Follow Up

[Don Wilhelm]

David,

It will work if you can load it - and whether or not you can load it easily
is highly dependent on the length of the feedline.  The switchable balun
will help you obtain a match.

I would suggest a flattop antenna cut near resonance at 30 meters and a
feedline length that is near a halfwavelength long at 30 meters (even though
you may not plan operation on 30).  The key is to avoid extremely high
impedances at the feedpoint - if the sum of the feedline length and half the
antenna length is near a multiple of a half wave on any band, the feedpoint
impedance is likely to be high, similarly if that sum is near a multiple of
a quarter wave, the feedpoint impedance will be near 50 ohms (but that is
just a 'rule-of-thumb' starting point.

If you can obtain the feedpoint impedance of your proposed dipole for all
bands of interest, a bit of work with TLW (available from the ARRL website)
can help you determine a length of feedline that should work for all bands.
The KAT1 has a good matching range, and the switchable balun extends it.  I
would say if you can keep the impedance at the balun end between 20 ohms and
1200 ohms you should be successful, but you need to stay away from points
that are highly reactive as well.

After all the 'figuring' is done on paper, put it up and try it - it is
quite wise to verify whether it works or not before you take off and try to
use it at a portable location.

73,
Don W3FPR


> -----Original Message-----

>
> Whoops!  I should have added this when I was composing last
> night.  I have the KAT1 tuner
> installed.  At the present, my four band module is for 40, 30,
> 20, & 15.  I plan on at least
> operating on 40 & 20 for sure, and possibly 15 if the SWR isn't
> too bad. Original message below
> for reference:
>
> Howdy Everyone,
>
> I am seriously considering the purchase & construction of a BL2
> switched balun so I can construct
> a lighter dipole antenna for field use than the dipole I have
> been using with my K1-4 (#2051).  I
> am planning on taking the K1 down to TX over Christmas and I
> don't want to take the heavier dipole
> I have with me like I did this past summer.  It's rather bulky
> and takes up valuable suitcase
> space.
>
> Here is my plan: Construct a 20 and/or 40 meter 1/2 wave dipole
> and feed it using standard TV
> twin-lead as my feedline (found in any hardware/home improvement
> store), and some #18 wire (I have
> some on hand).  Since the antenna would be balanced, I would
> attach the twin-lead to the balun and
> the balun to the back of my K1.  I am thinking that this design
> would make for a good performing,
> lightweight antenna that will be easier to pack & set up.
>
> Questions:
> 1.  Will the BL2 work well with TV twin-lead antenna I am going
> to build?  There's no sense in
> buying it if it won't work with this antenna.
>
> 2.  What kind of luck have those of you who have built it had
> with fitting it into some sort of
> plastic or metal enclosure?  What works and what won't?
>
> 3.  Will I need to do any sort of grounding with this?
>
> I'd really like responses from those who either (A) own one OR
> (B) do a lot of antenna homebrewing
> & experimentation.
>
> Many thanks,
>
> David
> KC9EHQ
> K1-4 #2051
>