Topband: Beverage Noise pickup

[Clive GM3POI]

Following on from Beverages over Radials I was considering Tx antenna noise
coupled into a Beverage.
    If  for example when putting 100W into a Tx antenna I get 1W  into the
Beverage Coax can I assume that the noise coupling of those two Antennas is
-20db  or are there other factors at work as well that make it worse or
better than 20db. My guess is that it is a good ball park figure. 73 Clive
GM3POI