Jan, in the book Transmission Line Transformers
by Jerry Sekick, W2FMI
second editon published by ARRL
there is the best solution to connecting 450 ohm
balanced line to 50 Ohm coax.
On page 9-33 section 9.5.3 Rhombic Antennas there
is a compound balun for matching 50 coax (unbalanced)
to 600 Ohm balanced line. It will work over a range
of 500 to 700 Ohms. It should work OK at 450 Ohms.
If you modify the position of the tap on the input
transformer it would be exactly 450 Ohms. The bandwidth
of this balun is 7 Mhz to 30 Mhz. It is usable from
1.8 Mhz to 54 Mhz.
I assume your nominal impedance varies above and below
450 Ohms. This transformer would change those variations
down to near 50 Ohms where a standard tuner would work.
It would seem sombody should sell this balun already
assembled.
Best regards, Jim FitzSimons W7ANF
Jan Ditzian wrote:
>
> Sherrill,
>
> I want to try what you have suggested, but I want to make sure that I
> understand what to do.
>
> I have Model 229 (manual) and Model 253 (automatic) tuners and 450 ohm
> windowpane line coming into the house from an 80-meter dipole 700 feet
> away. I installed this feedline by terminating the windowpane line in a
> 1:1 Amidon balun outside the shack, and then coming into the shack with
> about ten feet of RG-8 or 213 (I
> cannot remember which). Now that I have lived with this for a while, I
> realize that the windowpane line could come directly into the house,
> because the antenna cable entrance is simply a PVC L connector through
> the wall of the house. (I use a sophisticated temperature insulation
> barrier made of old sweat socks stuffed into the L connector, coupled
> with using the amplifier in cold weather to maintain the hamshack
> temperature; I washed
> the socks).
>
> Now, if I were to put the Amidon 1:1 balun between the tuner and the
> amp, how would I do it? Here are the specific questions:
>
> * Where does the balanced windowpane line connect; to the unbalanced
> coax antenna connector of the tuner?
> * Where does the balanced side of the balun connect; to the
> unbalanced connector of the tuner meant to go to the amp or radio?
> This would mean that the unbalanced side of the balun goes to the
> radio.
> * I am pretty sure that you are not recommending that I use the
> balanced antenna connection on the tuners, since this is simply
> another balun.
>
> Clearly there are connector mismatches, but I really don't care about
> that, as long as the electrical approach is correct.
>
> I also realize that I may get more RF than I want in the hamshack, and
> that may cause me to rethink the project.
>
> Thanks and 73,
> Jan, KX2A
>
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