Connecting the old Mark~III formatter to an upgraded Mark~IV recorder needs some extra care. The old formatter enumerates tracks with Mark~III numbering scheme where tracks 1--28 correspond to Mark~IV/VLBA tracks 4--31. So, the odd output connector (J11) actually supplies even Mark~IV tracks and vice versa.
Date: Fri, 20 Jan 1995 09:30:16 -0500 (EST)
From: Dan Smythe <dls@card.haystack.edu>
Subject: Mark3 to Mark4 cabling
Herewith are the directions for connecting a Mark III
Formatter to a Mark IV Tape Recorder.
These directions are also available for anonymous ftp from
card.haystack.edu in the file pub/mark4/mk3tomk4.wir.
This chart takes care of the fact that Mark IV is using the VLBA
head numbering scheme wherein Mark III heads 1-28 <-> VLBA heads 4-31,
so that ODDS -> EVENS and EVENS -> ODDS.
The Formatter/Recorder cabling for a Mark3/Mark4 system should be:
(Mark III (Mark IV (WRITE
Formatter) I/O BOARD) DRIVER#1) (STACK1)
J11 ------->J7--J8------->J5(EVEN)J7 -------> EVEN VLBA HEADS
ODDS J3<------- MON I/O
WRITE#1 POWER------>J1
(Formatter) (REC I/O) (DRIVER#2) (STACK1)
J12 ------->J9--J10------->J6(ODD)J8 -------> ODD VLBA HEADS
EVENS J4<------- MON I/O
WRITE#2 POWER------>J1
Best regards,
Dan
An important limitation of this mixed-mode configuration is that it cannot enable/disable recording tracks arbitrarily. This functionality is moved to the Mark~IV formatter in a complete Mark~IV system. However, recording voltage can be independently switched on or off in both write modules. Thus, if special care is taken in the schedule (and/or schedule procedures), recording can be enabled for even tracks only, for odd tracks only, or for all tracks. These limitations and the required test adapter cables are described in the following message.
From Dan Smythe (Haystack) in March 1996:
In order to get the EVN Mark IV stations running with full Mark IV
capability more quickly after the June session, I suggest that they
upgrade their tape transports, and then calibrate and test their
Mark IV Tape Recorders before the Formatters are ready. This message
describes the disadvantages of such an approach, and how to operate
this combination in Mark III Modes A, B, and C (but not E).
The VLBI station at NASA's GGAO in Maryland has been using a Mark IV
tape recorder with a Mark III Formatter for Mode C experiments during
the past three years. The only problem with this arrangement is the
fact that the Mark IV tape recorder has replaced the track enable
feature with a stack enable feature, so that it is not possible to use
the automated calibration schedule on this combination without using a
special wiring adapter, and Mode E observations are not possible.
This arrangement requires a pair of adapters between the Mark III
Formatter and the I/O Board on the Mark IV Tape Recorder to provide an
additional clock, and signals for VLBA heads 2 & 32, to the I/O board.
These adapters are made from a 3M Part No. 922576-50-I, by connecting
pins 13-18 to pins 35-40, on the side, and removing straight-thru pins
35-40. (If these adapters are used for a Mark III recording, the data
for Mark III heads 14-17 is sent to VLBA heads 2,3,32&33 also, in order
to test all 32 heads.) The VLBA even output of the I/O Board, and the
VLBA even heads of stack 1, are connected to the Stack 1 Write driver,
and the odd outputs and heads stack of stack 1 are connected to the
Stack 2 Driver. Then the Mark IV Field System command 'enable=stack1'
will enable the odd Mark III (even VLBA) heads and 'enable=stack2' will
enable the even Mark III heads. 'Enable=stack1,stack2' will enable all
heads. Stack 2 is not used for writing, and the write cables for stack
2 are not connected.
For calibration, only head 15 is enabled, so an adapter cable, with only
pins 21,22,39&40 connected, is used between the I/O board and the Stack 1
write driver. The three ENABLE=15 commands in hdcal.snp are replaced
with 'enable=stack1'.
With these simple adapters, the upgraded tape recorders can be tested
fully on all 32 Mark IV tracks with a Mark III formatter. Then when the
Mark IV formatters are ready, plug them in, edit 'equip.ctl', remove the
adapters, and everything should work. Note that the firmware to enable
a single output from the Mark IV formatter is not yet available, so the
calibration adapter mentioned above is still required even with a Mark
IV Formatter.
If these adapters are used for a Mark III experiment, the data for
Mark III heads 14-17 is also sent to VLBA heads 2,3,32&33.
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