I have just put up an 80 Meter End Fed Flexweave wire. Its about 63 feet
long and fed direct with 50 Ohm coax at the far end of the garden. The
shield is connected straight down to a ground earth stake at this point and
it is tuned for 3.700 MHz. It receives better than any thing I have used so
far, but it is very death on 40 meters. Almost unusable.

Is there a reason for this?

The antenna is only up at 20 feet and my old G5RV is only 6 feet off the
ground at the moment and receives far better on 40 meters than the End Fed
wire.

73 Andy