I received some great documents on narrow banding RTK radios from Pacific Crest a while ago:
Pacific Crest Product Bulletin – Narrowbanding Update
Configuring radios for narrowbanding
Applying for a 25 kHz FCC license
Coupled with my previous comments: [ Narrow Banding RTK Radios ] and the update [ Chapter 2 ] there is a pretty good knowledge base.
iG GPS 