To: File file: vlba4_training_exercise2

From: Jon Hagen

Date: Nov. 5, 2002

Subject: Running Jon's Tape

The tape of Nov 5, 2002 has data on all 36 heads) on the following tracks (head positions). Four passes were made as follows, writing, respectively, tracks 7,9,5, and 6:

Track 7 (fwd recorded 80 ips, 4 Mbps),

Track 9 (rev recorded 80 ips, 4 Mbps),

Track 5 (fwd recorded 160 ips, 8 Mbps) and

Track 6 (reverse recorded at 160 ips, 8 Mbps).

All other tracks, ie. are clean, i.e. no signal.

Run the tape as follows:

Clean the recorder heads with isopropyl alcohol and Q-tips, using motion in one direction, perpendicular to the recorder plate.

Start the field system and mount the tape. Load the tape using rec=load.

Type tapeforma to assign the tracks the same head positions used in recording the tape. The monitor response will indicate the head stack positions, in microns, assigned for each track.

Type repro=read,2,3,read,alt1,alt1 to connect the decoder to heads 2 and 3 (the first two heads used in our VLBA4 recorder). The equalizer default, alt1, is for 80 ips or 135 ips (according to fs help), but no eye patterns can be seen at 135 ips with alt1. 5 ips; for 270 ips use alt2.

Type pass=7,7 to put both headstacks at the pass 7 position.

Start the tape drive by typing

st=for,80,off where for is the opposite of rev, 80 is the nominal tape speed that produces an actual tape speed of xx.xxx ips, and off means write current is off. (Note that on is the default).

(Is this write current a third enable, after tracks and enable?)

All the tracks on this tape were written at the same (maximum) tape density, 56 kbpi. Reading can be done at either 80 or 160 ips (or at other speeds). When reading at 160 ips, the data will be coming off the tape twice as fast as at 80 ips, so use alt2,alt22, in the repro command to select the proper equalizer.

Eye patterns should look the same in either direction, but the decoder can't decode data unless the tape is moving in the direction in which the data was written.

The recovered clock, seen on the scope, will be a square wave whose frequency is the

frequency of the output data. The tape was written at 4 Mbps and 80 ips or at 8Mbps and 160 ips, so the recovered clock will be 4 MHz at 80 ips or 8 MHz at 160 for any of the tracks.

Monitor the eye pattern on the scope.

Get parity error counts on decoder display using decode4=dqa 400 to display the number of parity errors per million bytes. (600 is the nominal limit).

Or set up for parity error display on screen using parity=,,,,2,3,4,5 for example to

get the error rates for tracks 2,3,4,5. Start the test by simply typing parity.

Stop the tape by typing et (end tape).

Read the tape while backing up by typing pass = 8,8 and then st=rev,120,off