Topband: Top Band Antenna

[rodger bryce]

Gentlemen, I have the following which I would like to turn into a topband antenna if possible. My mast is approximately 40 feet high and there is rotor cage with a 10 foot stub mast, on the stubmast I have an 8 el.log periodic and above that a rotary dipole for 30/40m. 
 
I attached a drop wire at approx. 38 feet high, I grounded this wire and tried to grid dip the wire plus mast, all as per ON4UN's book "USING THE BEAM TOWER AS A LOW BAND VERTICAL" the results were zilch, nadda nothing at all, no dip anywhere on any band. I used the MFJ 259B with the GDO accessory.
 
1. Am I doing this all wrong......highly possible.!!
2. Is the mast not high enough to be used for top band.?
 
I am totally out of my depth here.........so any guidance would be much appreciated. 
 
Many thanks, Rodger/GM3JOB