Jan;
First I do suggest that you connect the 450 line direct to the balanced
terminals of the tuner. Take advantgage of the internal balun. As to
RF in the shack, if the antenna is reasonably well balanced the the line
is kept away from trees, buildings, metal things i.e. at least 10 times
the spacing between the conductors then the likelyhood of unbalance is
nil. Therefore RF in the shack is also reduced.
As to putting a balun between the tuner input and radio, my suggetion is
DON'T! There is a difference between a 1:1 current balun and a 1:1
voltage balun. A 1:1 current can be used between the radio/amp and the
tuner input. I seem to recall that some 40 - 50 beads of #43 material
is good for HF. The size of the beads will be 1/2" ID and about 1" OD
and 1/4" to 3/8" thick each. It's simply a RG-8 or RG-213 coax jumper
with a PL-259 on each end with the beads over the outside jacket of the
coax. These are sometimes called a choke balun.
As to a voltage balun, it's several turns of wire, #8 or #10 AWG with
teflon insulation, 2 separate windings, over a donut core. A 2 KW core
is about the size of a real donut. 3" - 4" in outside diameter, 1"
thick with about 1.5" hole in the center.
Amidon has excellent technical information on this stuff.
73
Bob K4TAX
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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