David wrote:
But if the field of the radials cancels out, is there any benefit in having
radials in receive mode?

Yes. If you eliminate the radials, you have a single conductor wire (the
"antenna") connected to a feedline or receiver. The feedline or receiver
has two terminals which comprise an electrical circuit. If you leave one
of those conductors open circuited, current induced by the passing
signal will not flow from the "antenna" to the receiver or feedline. In
practice, it's nearly impossible to really open circuit the other
conductor (that is, the one not connected to the "antenna") -- the
outside of the feedline, if coax, will become the other half of the
antenna, as will anything conductive connected to the receiver chassis.
This is often undesirable because those conductors are more likely to
receive noise from local sources than if the entire antenna is in the
clear. It will also distort the antenna pattern, possibly in a major way.

I've put "antenna" in quotes because the vertical wire is only half the
antenna. The other half is either radials or, if radials are missing,
the other conductors I mentioned.

Roy Lewallen, W7EL