[Elecraft] Corrected Elecraft BL1 balun description $ price]

[Robert Friess]

Hi George,

While it is certainly true that the probability of finding exactly 200 ohms,
50 ohms or any other fixed impedance at the end of a unmatched transmission
line is low, the BL1, like all low loss transformers, depends on a
particular impedance presented to the secondary in order to produce 50 ohms
at the primary.   Termininating the BL1 in 200 ohms allows us to measure the
performance of the transformer.  The BL1 frequency response when terminated
in 200 ohms is much wider than most baluns and should allow reasonable
frequency
response and balance over a wider range of load impedances than is usually
found.

We decided that there were many cases where matching to a higher impedance
balanced line would be desirable.  Folded dipoles and other resonant loop
antennas are examples.  Furthermore, most antenna tuners have limited
matching capability, so even in the unmatched case, a step-up to higher
impedance may well extend the capability of an antenna tuner to match an
arbitrary load.

That said, it is a simple matter to rewire the secondary connections of the
BL1 to 1:1 if that is your preference.

73,
Bob, N6CM

> -------- Original Message --------
> Subject: Re: [Elecraft] Corrected Elecraft BL1 balun description $ price
> Date: Wed, 15 Oct 2003 10:04:59 -0500
> From: George,  W5YR <w5yr@att.net>
> Organization: W5YR
> To: Eric Swartz WA6HHQ - Elecraft <eric@elecraft.com>
> References: <3F8CD599.9010503@elecraft.com>
>
> Eric, I am rather curious as to your choice of a 1:4 balun. Is it
configured
> as a current balun or a voltage balun? What was the basis for the 1:4
design
> decision?
>
> For most applications involving ladderline or twinlead, the 1:1 current
> balun has proved to be the least transparent and most efficient design. In
> most cases, it will be difficult if not impossible to provide the 200 ohm
> resistive load required for proper balun operation. For multiband antenna
> use, it is highly unlikely that on any band will the line input impedance
be
> even close to 200 ohms resistive. Accordingly, there will be just as many
> instances in
> which a 1:4 balun would make a difficult matching situation worse as there
> are in which it might help.
>
> For these and other reasons, I am quite surprised that this balun design
was
> selected. If there are no company secrets involved, I would be very
> interested in knowing your reasoning for choosing this design over the 1:1
> current balun.
>
> Thanks!
>
> 73/72, George
> Amateur Radio W5YR -  the Yellow Rose of Texas
> Fairview, TX 30 mi NE of Dallas in Collin county EM13QE
> "Starting the 58th year and it just keeps getting better!"
> w5yr@att.net
>
>