HFU HF Underground

Technical Topics => Equipment => Topic started by: k6sti on June 13, 2021, 0035 UTC

Title: 13.56 MHz Antennas
Post by: k6sti on June 13, 2021, 0035 UTC

Four antennas over three types of ground:

http://ham-radio.com/k6sti/hifer.htm

Brian

Title: Re: 13.56 MHz Antennas
Post by: syfr on June 19, 2021, 1153 UTC

Thanks! The power in re ground quality is quite interesting too!

Title: Re: 13.56 MHz Antennas
Post by: k6sti on June 19, 2021, 1222 UTC

Unfortunately, there's no simple way to determine your local ground quality. Here is a ground conductivity map:

http://ham-radio.com/k6sti/gcmap.gif

I couldn't find a map for ground dielectric constant.

You can interpolate legal power if you think your ground quality is somewhere between the three given. Only the ground-plane legal power is quite sensitive to ground quality.

The other unfortunate thing is that the legal power and radiation patterns change when you alter antenna height. I picked 30 feet for the horizontal antennas because that height is not hard to reach with a push-up TV mast. A ground-plane is less sensitive to height. I picked 20 feet for the base because it keeps the ends above head height.

Brian

Title: Re: 13.56 MHz Antennas
Post by: k6sti on June 19, 2021, 1230 UTC

This table of ground constants provides some description:


                     Earth                    Diel  Cond    Ground
                    Surface                  Const  mS/m   Quality
     --------------------------------------  -----  ----  ---------
     Salt water                                81   5000  Excellent
     Fresh water                               80    1
     Pastoral, low hills, rich soil            20   30    Very Good
       (Dallas TX to Lincoln NE)
     Pastoral, low hills, rich soil            14   10
       (OH and IL)
     Flat country, marshy, densely wooded      12    7.5
       (LA near Mississippi River)
     Pastoral, medium hills and forestation    13    6
       (MD, PA, NY, except mtns & coastline)
     Pastoral, medium hills and forestation,   13    5    Average
       heavy clay soil (central VA)
     Rocky soil, steep hills, mountainous   12-14    2    Poor
     Sandy, dry, flat, coastal                 10    2
     Cities, industrial areas                   5    1    Very Poor
     Desert (southwest ID)                      3    0.55
     Cities, heavy indust areas, high bldgs     3    0.1  Extr Poor

Brian