Here is the link you were looking for:

http://geodesy.noaa.gov/cgi-bin/HTDP/htdp.prl?f1=4&f2=1

This is your go-to friend for your NAD83 -> WGS84 converting needs!

You will find several other useful utilities at that site as well.

Hint:  When creating a base station location, you MUST convert your base station antenna position to WGS84 (not NAD83) and then use the resulting ECEF data in your RTCM messages if you expect the values you send to align with the work of others.

A typical output of this tool looks like the below:

 ****************************************
 HTDP (VERSION v3.2.5    ) OUTPUT

 TRANSFORMING POSITIONS FROM NAD_83(2011/CORS96/2007) (EPOCH = 07-02-2016 (2016.5000))
                          TO WGS_84(G1674)            (EPOCH = 07-02-2016 (2016.5000))

 myBaseStation                 
  LATITUDE     37 25 28.33041 N     37 25 28.32234 N        0.00 mm/yr  north
  LONGITUDE   122 08 47.69397 E    237 51 12.28769 W        0.00 mm/yr  east
  ELLIP. HT.             -19.923             -17.869 m      0.00 mm/yr  up
  X                 -2698470.874        -2698472.204 m      0.00 mm/yr
  Y                  4293972.147         4293973.416 m      0.00 mm/yr
  Z                  3854903.946         3854904.997 m      0.00 mm/yr

What is a Datum and Why should I care…

Trust us on this one.  You will need to know the at least basics of reference frames and datums if you hope to operate an RTK network like SNIP, where different data sources / streams that you collect could express the raw data in different systems. Some useful reading to help you along the way:

https://en.wikipedia.org/wiki/Geodetic_datum
An overview of the key terms and concepts.

http://www.ngs.noaa.gov/TOOLS/Nadcon/Nadcon.shtml
The launch point page for the NOAA and NGS tools provided by USGS with commentary on their intended use.

http://www.colorado.edu/geography/gcraft/notes/datum/datum.html
Materials that were developed by Peter H. Dana, Department of Geography, University of Texas at Austin.

http://www.bnhs.co.uk/focuson/grabagridref/html/OSGB.pdf
While describing the datums used in Great Britten, this is in fact one the most readable texts you will find.

http://www.colorado.edu/geography/gcraft/notes/datum/edlist.html 
A cheat sheet of common parametric values; useful if you need to program this sort of stuff.

ITRF to WGS84 Questions?

Down to the <1cm issues?
Read this excellent educational article from the makers of QINSy:
https://confluence.qps.nl/qinsy/en/international-terrestrial-reference-frame-2014-itrf2014-29856813.html

Changing the Frame of Reference for a Base Station

Use the PFAT Translation tools and the ECEF Adjustment dialog to enter the new value you want.  Ideally, enter the new values using the ECEF section for greater accuracy and control.  SNIP will allow you to enter whatever you wish; it does not care what datum or frame of reference you use.  It checks only that the ECEF values are consistent and warns if the entered value represents a large offset.  Therefore, it remains your responsibility not to enter incorrect data that would introduce measurement errors to your end users.