Topband: Question - optimum number of radials

[DALE LONG]

I understand that 120 radials is the golden standard.  At what point is there no significant improvement?

How much worse is 60 radials?  How much worse is 24 radials (4 of 1/4 lambda and 20 or 1/10 lambda)?

This may have been discussed in the past, but if there is any engineering reference or field testing that has been done, I would like to know the results.

Thanks

Dale - N3BNA