[500kc] [Lowfer] Re: AMRAD Probe antenna part needed

[Bill Ashlock]

> does the shorter mobile coax feed mess up the performance  Bob K3DJC 
 
Bob, it actually it does not. With a probe at a fixed location it's not really the coax length that counts but the amount of capacity coupling it offers to ground. (This does not hold, however when you raise the antenna to a higher location above gnd and take advantage of a larger effective antenna length) The capacity to gnd needs to be somewhat greater than the capacity of the probe to ground (something like 8.85 pf per meter of antenna rod length). The car body and capacity coupling from there to ground makes this an excellent mobile antenna as long as you stay away from power lines and other E-field interference sources. Also the trees have a shielding effect and you need to be at least 100ft from them. If memory serves the gain is something like 6 db over a vertical probe placed right at ground level which has a 1uv per meter of antenna length sensitivity. I used this type for many field strength readings back in my loop radiation investigation days. (Which reminds me I need to get back to this at 500K)
 
Bill