[RFI] RF Choke Insertion Loss?

[Tony]

All:

Installed an RF choke at the feed point of my portable linked dipole and 
immediately noticed a significant drop in common mode noise while 
testing the setup at my QTH.

Isolating the coax from the antenna greatly improved the S/N ratio which 
I thought could help in the field when close to a noisy location.

This is probably a silly question, but I run QRP/CW when portable and 
was wondering if the choke can cause any appreciable insertion loss on 
the transmitted signal?

Tony