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Common mode Choke for Balanced Parallel Feed Line

Aug 26th 2015, 19:57

AG6CX

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
Zach:

Cannot seem to find any references in the literature to the use of CMC in parallel feed operation, say with 135 ft doublet fed with open wire to a link coupled tuner. Can you direct me to some resources or articles on the topic. Lots of stuff on coax fed CMC but nothing for parallel feed lines.

Thanks,

AG6CX
Aug 26th 2015, 20:14

W1VT

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0

Typically, the range of impedances expected in an open wire system suggest impedances that are too high for practical useage of common mode chokes. This is especially true if you look back just a few years, before people started measuring chokes with network analyzers that provide both reflection and transmission measurements. Based on available data, it made sense to dismiss the use of CMCs with open wire systems.

Zack W1VT
ARRL Senior Lab Engineer
Aug 26th 2015, 20:33

AG6CX

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
Thanks for prompt reply Zack.

Was thinking of using Balun Designs model 1171 balun between open wire and balanced link-coupled tuner as common mode choke. Will this not enhance minimization of CMC without impairing efficiency?


Aug 26th 2015, 21:05

W1VT

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0

Perhaps you could work with the manufacturer to obtain a 2 port model of the balun and model it with intended open wire systems to estimate the efficiency. L.B. Cebik used to do similar investigations for other hams, as a retired math professor, but he is now a silent key. His work is now behind a paywall, as he realized that a volunteer wouldn't maintain the site without some financial incentive.

Zack Lau W1VT
ARRL Senior Lab Engineer
Aug 26th 2015, 21:18

AG6CX

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
Sadly have encountered the paywall and the general arrogance of the wall keeper.

Thanks.

73
AG6CX
Aug 26th 2015, 21:34

W1VT

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
One way to measure transmission line losses is to build two identical systems and run them back to back, and then measure the insertion loss of the back to back system.

Another approach, is to build the antenna system and measure the balun heating, perhaps with non-contact IR thermometer. There are even hams who have access to thermal imaging cameras, as these have become more affordable.

Zack Lau
ARRL Senior Lab Engineer
Sep 11th 2015, 14:05

W1VT

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
http://www.eham.net/ehamforum/smf/index.php/topic,28698.10/wap2.html
This long post suggests that the balancing device should be up in the air near the feedpoint rather than between the open wire and the transmatch.

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