Topband: Measuring field strength

[Greg - ZL3IX]

Dan Zimmerman N3OX wrote:
> I've had lots of good responses regarding putting radials out to the
> front yard.  I'm going to run radials around to the front of the
> house, possibly by putting a perimeter wire around the house.
>
> I'd like to make some field strength measurements while I'm working on
> it; I'm not worried about absolute measurements; I just want to make
> some relative ones.
>
> There's a park across the road from me... I think I can get up to 5
> wavelengths away from my antenna.  (I keep thinking that I should have
> a north-pointed beverage along the river but I doubt the Maryland
> National Capital Parks and Planning Commision would appreciate that)
> My gut feeling is that 5 wavelengths is sufficient for good relative
> comparisons.  I doubt I can get further away.  Closer would be more
> convenient for me.  How far away is far enough?
>
> Dan
> _______________________________________________
>   
The park will be more than enough, Dan.  All you need is for the wave 
impedance to settle close to 377 ohm, and that happens inside a wavelength.

By the way, how are you going to measure the field strength?  When I 
embarked on a similar exercise, I used the AD8307 log amp.  It's pretty 
sensitive, linear, and gives a DC output of about 25 mV/dB.  Just put 
some kind of filter in front of it to keep out any nearby BC stations.

73, Greg, ZL3IX