To: File file: vlba4_training_exercise3

From: Jon Hagen

Date: June 6, 2002 expanded Nov. 11, 2002

Subject: re-writing Dan's Tape

Dan's tape is short and has dropouts. A similar tape was written as described below.

All 36 heads are fed the sign bit from bbc01, as specified in the procedure "allbbc0". The tape was first erased using the bulk demagnetizer. The tape was then written as follows:

proc = aoproc (tells field system what directory to use when looking for "allbbc0")

allbbc0 (we should have named this procedure allbbc1. It assigns data from the sign bit of digitizer 1 to every head).

tapeforma (standard macro to assign headstack positions for each pass number)

pass=7,7 (first pass will be written at assigned headstack position no. 7)

tracks= v0,v1,v2,v3 (enable the formatter's output drivers)

enable= g0,g1,g2,g3 (enable the recorder's write drivers)

form=m ("manually" commands the formatter to set the data-to-head assignments called for by the "trackform" command inside allbbbc0, and to set the output enables called for by the "tracks" command).

st=for,80,on (start the tape in the forward direction at 80 ips with write=on)

let tape run for 40 minutes and stop.

et

now record in reverse direction, back to the the beginning in pass 9 position

pass=9,9 st=rev,80,on

Stop the tape before it runs off the take-up reel and then move on back to the zero point

et rec=0

Now write in pass 5 position in the forward direction at 160 ips.

pass=5,5

To keep the tape densitity at max (56k bpi) we'll bump the sample rate from 4 to 8 MHz.

form=m,8 (for the previous passes, 4 MHz was set by the field system as the default)

st=for,160,on

stop after 20 min

et

Write backwards in the pass 6 position to the beginning of the tape.

st=rev,160,on

stop before running off the take up reel

et