[Mesorah] Why is the guy's name Bigsan and not Bigtan?

[Zev Sero via Mesorah]

On 03/23/2016 06:04 AM, Micha Berger via Mesorah wrote:
> My husband thinks that after a shva nach (under the gimel) the next
> letter should have a dagesh in it, as for example in the name Ester.

Why does he assume the sheva is nach?   Why doesn't the lack of a dagesh
indicate that it's na`.

-- 
Zev Sero               All around myself I will wave the green willow
zev at sero.name          The myrtle and the palm and the citron for a week
                And if anyone should ask me the reason why I'm doing that
                I'll say "It's a Jewish thing; if you have a few minutes
                I'll explain it to you".