[Antennas] increased antenna bandwidths through a tuner, why?

[Sam Morgan]

I have a bugcatcher set with 1:1 at center frequency of 7.09 with no tuner.
It has a base coil taped for minimum swr.

When I check the 2:1 to 2:1 bandwidth it is about 76kc.

If I run it through my home brew T-tuner, and set the tuner to have the same 1:1 
at that same 7.09 frequency, I then get a bandwidth of 151kc. (not touching up 
the tuner further than when I set it to 1:1 initially).

The tuner is set with both caps @ 50% and the (small) roller inductor is set at 
about 7 of 17 turns out from minimum inductance.

It makes me happy, sure, but I'm wondering if someone would explain it to me.
How does it increase the bandwidth if the same 50ohm feed point is there with or 
with out the tuner.
-- 
GB & 73's
KA5OAI
Sam Morgan