Topband: RF choke woes??

[Jimmy Burrell]

Just built a wire vertical dipole (Lazy H style) yesterday for 80m  
(very similar to the one shown on EI7BA's web site here ).   Since I  
am feeding the antenna asymeterically I knew an RF Choke would be in  
order.  EI7BA recommends an FT240-61 with 12 turns of RG-58.  Not  
having the recommend ferrite at hand, I proceeded to homebrew a choke  
out of a large diameter (~7") plastic coffee can and 20 turns of  
closely spaced RG-58 well secured.

This apparently isn't good enough??  When testing at the antenna with  
my MFJ it is "spot-on" correct just like the model and resonant at  
the design freq. of 3.830.  However when using the homebrew RF choke,  
resonance is just above 4 MHz.  I did test without a choke at all and  
resonance was much much higher.

Is this not enough choke at this frequency?

Thank you,

Jim...
N5SPE