Topband: Grounds

[Mike Greenway]

I am building a new two wire beverage and have built many in the past that seemed to work okay but I am paying close attention to detail on this one.  I have a couple of questions to start.  Most all agree that the antenna xfmr ground and and the coax ground should be separate.  How much distance between the two ground point is recommended for this?  Also is there a problem using the same ground for both coax feeds?  ON4UN recommends a common mode choke about 15 feet away from the feed point but at present I am not installing those yet.
73 Mike K4PI