Topband: Rationalizing my radial field through measurement

[Tom W8JI]

> If I wanted to measure the radial and feedline AC current, not having any 
> RF ammeters, I might just take a #47 lamp or other small pilot lamp and 
> stick it in series with the radial and transmit into it. 40 mA will make a 
> #47 lamp glow very dimly. Is this a good thing to check on?

Probably not with series lamps, unless the radial impedance is pretty high. 
The measuring device or system must not significantly change the series 
impedance of the path or it will alter the results.

>If I find that some radials don't carry enough current to light up the 
>lamp... is that a sign that the low current radial is not needed?

Usually, but it also depends. Radials can have standing waves. What we 
measure at one point might not be what is happening 1/10th wave away.

>> If other radials are carrying way more than average current... is this a 
>> sign I need more radials in that direction? Or is it the other way 
>> around? Or is this all academic and I just need another few thousand feet 
>> of copper wire? :-)

I use one of these:

http://www.mfjenterprises.com/Product.php?productid=MFJ-854

I designed that device to measure very low current levels, and (if they 
calibrate it correctly and still build it the same) to be accurate. It also 
does not change the circuit much.

It's really a handy device for measuring current, it has a very wide dynamic 
range.

I'm just not sure if, for what you are doing, it is necessary. I'd just use 
as many radials as I could as straight and long as possible, but not over a 
quarter wave or more than 30-40. I think sometimes we make too much worry or 
magic over things. :-)