Topband: ground radials - how long should they be

[Paul Baldock]

I have a 130ft tower with 60 x 130ft ground radials (in "poor" soil). 
However on the tower I have various antennas including a 4 element 
40M beam on the top. Electrically the tower is about .4 wavelengths ( 
a little less than a half wave). I shunt feed the tower and other 
than high Q it performs very well.

I haven't really noticed any difference in performance since I added 
the big antenna on the top and retuned the match(other than the high 
Q), but of course I can't do an A/B comparison.

Somewhere in the back of my mind I recall somebody saying that the 
radials should be as long as the tower is tall. Is this true? If so 
is this electrical length or physical length?

- Paul KW7Y G3UID