Actually that's not true. A lot of baluns are wound with balanced transmission
line.
Wes. N7WS
Sent from my iPhone
> On Dec 11, 2017, at 3:49 PM, Bert <balmemo@sympatico.ca> wrote:
>
> Hi Bill,
>
> Choking the window line is not a good idea - you'll choke the signals too.
> Common mode chokes are mainly used for coax cables and multi-conductor
> cables. I'm sure you'll get many more detailed replies from the experts.
>
> Good Luck!
>
> Bert, VE3NR
>
>
>
>> On 12/11/2017 4:33 PM, k7wxw wrote:
>>
>> Yesterday the wind brought down my doublet, which I mostly see as an upgrade
>> opportunity, at least once I finish pulling tangles of wire out of trees.
>> While a window line fed doublet is a well-known beast, and the one I had up
>> worked okay, I hope the new version will perform better by taking into
>> account my particular installation limitations. As I worked on the design,
>> I came up with a couple of questions...
>>
>> I apologize if this is too much detail, or whatever.
>>
>> I am putting up a centerfed doublet to cover 80 through 10 meters, focusing
>> on 80, 40, 30, and 20 meters. I plan on feeding it with a random length of
>> 450 ohm window line. I have a Johnson Matchbox and Dentron Supertuner and
>> can use either to match the antenna to my rigs. My antennas come to a
>> common connection panel, which is mounted on an ground rod. I rarely run
>> more than 25W and never more than 150W.
>>
>> For a number of reasons - including the fact that it won't be quite level,
>> it is only up about 30 feet and part of it runs over the house - the antenna
>> will not be balanced. If I install a 1:1 current choke built using two
>> stacked FT-140-43 toroids at the antenna feed point, is it likely to survive
>> given the wide variation in feedpoint impedance over the operating frequency
>> range?
>>
>> I originally planned on using a Morgan balanced line lightning supressor.
>> Unfortunately, it is only rated for input and output impedances of 300 to
>> 600 ohms, a condition that is impossible to meet in a multiband antenna. My
>> alternative is using a 4:1 balun, followed by a polyphase lightning
>> suppressor. Same question about this balun (stacked FT-140-43)... how will
>> it do given the variation in load impedance over the operating range?
>>
>> The 4:1 balun at the base of the feedline has the added advantage that I can
>> avoid running window line into the house (I am doing that now) which is a
>> PITA.
>>
>> Bonus question: I know that expecting baluns and common mode chokes to work
>> well over 3 to 30 Mhz is, well, optimistic. Will I get better common mode
>> suppression at the feedpoint by using two chokes, material chosen to
>> optimize different portions of the operating range?
>>
>> I have read K9YC's guides, along with a lot of material from W8JI and others
>> but I haven't quite figured out how to figure out the answers to my
>> questions.
>>
>> Thanks for any help and 73 de bill K7WXW
>>
>>
>>
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>>
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