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Author Topic: tuner placement  (Read 467 times)
K2VJK
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Posts: 13




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« on: February 21, 2008, 07:51:38 AM »

I'm wondering about feeding a horizonal loop via coax to a SGC tuner to 450 window line to the antenna. In theory, it looks good. Anyone doing this?
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WA7NCL
Member

Posts: 625




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« Reply #1 on: February 21, 2008, 08:12:02 AM »

In theory the tuner is single ended.  The window line and the loop are balanced.  So in theory you have a problem of getting the balanced loop and feed line to the antenna tuner.

I have experimented with using a 1:1 current (choke) balan from the ATU to a balanced feedline.  It seems to work.  I am sure that for some matching conditions it is not the best.

I would say your best bet is to do a little experimentation and decide if the system works well enough for you or not.  Just be aware that if you feed the balanced line directly, you may experience problems with feed line radiation and RF on the ATU control lines and coax feed.
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WA3SKN
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Posts: 5556




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« Reply #2 on: February 21, 2008, 09:10:31 AM »

The SGC has an unbalanced output... recommend a balun be used, either 1:1 or 4:1... but it works Great!
The Loop will work better a low heights than a dipole, and can be used multiband.

-Mike.
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K9ZMD
Member

Posts: 173




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« Reply #3 on: February 21, 2008, 09:16:02 AM »

Yes, I've used the configuration you described.  It allowed use of a horizontal loop, as well as various doublets, as multiband antennas. SGC instructions may state that no balun is needed for that configuration (as they do for my SG-239); however, you may then experience frequent, unwanted "retunes" on voice peaks or in time with keying on some bands.  I've treated that problem by adding a 1:1 choke balun between the tuner and the balanced line.  

As WA7NCL mentioned, common mode currents may still be present on the coax between transceiver and ATU, and/or on any ATU control & DC lines.  If that creates RFI problems for you, resolve them with ferrite chokes on the coax and ATU cables.
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