It seems there is a good solution to a single common mode choke for
balanced lines over all of HF. See the article in November 2017 RadCom
(RSGB) "An effective, easily made HF Balun". G3LNP describes a 4:1
balun for all band doublets fed with REAL open wire feeders, with CM
rejection on the order of 40db.
Additionaly, consider G3TXQ's measurement of punched ladder line
losses. http://www.karinya.net/g3txq/wet_ll/
I evangelize using real open wire, easy to make or buy. Examples:
http://trueladderline.com/w7fg-design-600-ohm-open-wire-feedline/
http://www.73cnc.com/product_p/ls100.htm
Grant KZ1W
On 12/11/2017 16:15 PM, Bert wrote:
We're talking about a common mode choke, not a balun/transformer.
Bert, VE3NR
On 12/11/2017 7:08 PM, Wes N7WS wrote:
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
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|