[TowerTalk] Forty Meter height question..

[K7LXC--- via TowerTalk]

>  I would appreciate some suggestions and guidance. I have a  40  foot 
Rohn 55 
tower mounted on top of a building. The top of the  tower is 100  feet 
above the street.

>  At present there is  a Force 12 XR-5 just above the  tower, which plays 
very well.
I am  planning to place a Force 12 Delta 230/240 above the  XR-5 on the 
same  mast. 
They will be 8 feet apart.
Question:
The two elements for 40  meters will only be about 48 feet  above the roof. 
Since this is less  than a full-wave length in height  above the roof, low 
angle radiation  would be affected, does it make sense to put  up ?   Would 
a  
>  slightly longer mast fill the gap ?
 
    Go with what you've got - I wouldn't do anything.  While the antenna 
will be 48 feet above the roof, it really doesn't electrically  see the roof 
much. Methinks the near-field is pretty complicated what with other  
structures and metal lumps of HVAC, etc. so it probably doesn't matter much  
difference where it's mounted. 
 
    Here in the Pacific NW, the question about whether  to make a change or 
not comes down to "Will the JA's tell the difference?" Or in  your case, 
"Can the EU's tell the difference?" In many cases, the answer is  "probably 
not". Also for example, a 10' height difference is just a fraction of  a 
wavelength so the change is only very incremental. 
 
Cheers,
Steve    K7LXC
TOWER TECH