[Antennas] Question on Balun and use of one and type???

[Charles Greene]

Steve,

I'm not sure that a balun is the right device for this application.  First 
try changing the length of your transmission line by about 1/4 wave length 
on the band that has the worse RF in the shack.  You might try a coiled 
coax balun, design parameters in the ARRL Handbook, to see if this 
helps.  You might also try rearranging the grounds in the shack to see if 
this helps.  I would need more information on the impedance (R+jX) of the 
antenna at the feed point and the length of the transmission line, any 
grounds and their locations, to figure it out.

Also shows why using 9913 outside is a bummer.  It's a great inside feed 
line, if you have some spare and don't know what to do with it.

At 02:45 PM 7/14/2002 -0400, Steve Jones wrote:
>I have an antenna called a German Quad which is supposed to be or have four
>sides but due to my landscape layout, I could only come up with three
>supports. The antenna is 236' in length, put up horizontally to the ground
>and 40' up in the air on all three coiners. It is feed in one corner with a
>matching stub of 28' of 450 ohm ladder line that drops vertically down from
>one of the three coiners and then to coax and in to my shack where I use a
>Drake MN2700 tuner to tune for use on other bands such as 10-20 meters. It
>is almost flat across the entire 40 meter band and about 200 khertz on 75/80
>meter band. Well this antenna has worked great until about a year ago I
>noticed my SWR was going through the ceiling and the tuner was getting very
>warm. I decided to replace the 9913 as this was the only thing that I could
>determine was causing the problem. When I cut the run at the connection of
>the 450 ladder line and coax, water ran out of the 9913 like a river.
>Problem solved I thought. I had about a 100' run from my shack to the coax
>joining the ladder line. Well the only thing I changed was the type of coax
>which is now LMR400 because I had a 60' section laying around, and the
>length which went from about 100' down to 60'. Now I get RF in my shack like
>crazy, I can't even tune the bands 10-20 and run any power without so much
>RF, I can't even operate and enjoy it, and here lately, I have noticed my
>SWR curves have changed somewhat from a tuning chart I did and the tuner is
>getting hot again, especially on 75/80 meters.
>
>Does anyone of any thoughts on how I could correct this and get this great
>antenna working like it use to on 10-75/80 meters. I never used a balun
>before and then antenna worked great and again the only thing that has
>changed is the length and the type coax I am using and it is hard to believe
>water has gotten in to the LMR400. I would appreciate any and all feedback
>that is positive and helpful, no insults or negativism needed here. Thank
>you in advance for your help and 73, Steve
>
>- - -
>
>Your moderator for this list is:
>Larry Wilson KE1HZ antennas-owner@mailman.qth.net
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73, Chas, W1CG