Andrew,

There is a good discussion on this at:

www.dxengineering.com/Products.asp?ID={022A1CDF-C417-4F8B-AF97-B1ED91AAE23A}&SecID=10&DeptID=33

You may need to cut and past that to get it to work. DX Engineering
is pricey, but they do know their stuff.


--
Alan
WA4SCA