I found a reference to vtserver on Johnathan Engdahl's web site  here .  It was written by Warren Toomey and can be found on his  web site . It seemed to solve a problem I had (if it worked) of how to get system images onto a PDP-11 so that they could be used.

Fundamentally vtserver is a program that runs on a Unix or Linux host that emulates a simple terminal and a virtual tape drive.  Also included in the package are standalone programs that can be downloaded to the PDP-11 (using vtserver of course) that allow copying of the data from the virtual tape device (the host) and writing it to a device on the PDP-11.  Since vtserver was derived from the standalone programs for BSD, it has pretty much full generality, so one could use it to perform standalone copies of packs between drives.  I guess it could also be used to copy from a real tape device to a disk too.

It's fairly simple to set up (just follow the directions in the  readme ).  I had it up and running on my Linux laptop in about 5 minutes (including the time it took to type 'make').

 vtserver 2.3a