[Mobile-Portable] 10 meter mobil high VSWR

[K7fe@aol.com]

I agree with a couple of the responses.  It's the grounding...............
The shorter wavelength of 10M compared to 40M make grounding more critical on 
10M.
Autos of today have less metal, so run not just a wire ground, but a 6" to 
12" wide metal strap from your antenna base mount to a good wide chunk of metal 
on your car frame, then tie your frame to the body with the same material in 
more than on place.  Use more than one screw (3 to 6 of them) at each point of 
"grounding".  Feeding your antenna with coax in 1/2 wavelengths can't hurt, 
but won't help over come poor grounding. 

If you wish to better match the 36 ohm feed impedance of your antenna to the 
50 ohm coax then use a matching coil at the base.  Since this is a monoband 
antenna then the matching need not be broadband.  I like to use a 10 turn, 3/4 
inch dia coil of # 14AWG.  Connect one end of the coil to ground, the other end 
to the antenna feed point at the base of the mount and solder the center of 
your feed coax to the coil at the point where the vswr shows the best match.  
You can use an alligator clip soldered on the end of the coax for easy 
adjustment to find the best turn on the coil prior to permanently soldering.  KEEP 
YOUR LEADS VERY SHORT!    Including the shield of the coax to ground.   This is 
extremly important at this frequency. 
Good Luck!  
My background is many years aerospace microwave and rf engineering, ham over 
40 years, and long time 10 meter fan who has worked over 100 countries on 10m 
mobil.
73,
Terry, K7FE


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