Документ взят из кэша поисковой машины. Адрес оригинального документа : http://www.naic.edu/~tghosh/dave Дата изменения: Tue Aug 7 22:34:11 2001 Дата индексирования: Sat Apr 9 22:40:48 2016 Кодировка:

>
> Thanks for you mail. We actually guessed that you might have
> been on holidays. Well, for the vsop run, we actually went back to the
> old FS (version9.4.18) + the S2 recorder. So, hopefully the P.I.
> will have his data.

Hi Tapasi,
some of the head-positioning problems, particularly with "headp" for
evaluating headcal for a VLBA4, have been fixed in 9.4.121 I think.
>
> Now we have to get back to the VLBA4 trouble-shooting again.
> We are planning to run Dan Smythe's latest testapev.snp and
> testapev.prc for VLBA4. Just now, I am unable to reach "dopey", but no
> doubt, it will be available soon. One point that Dan raised was that
> whether or not we ever used a thick tape on this recorder. As far as I
> knew before all these tests began, all our 20-tapes bought a year agao
> were thin. However, to my surprise, I found that 2/20 were listed on
> TRACK as "thick", and we had unknowingly used one of them recently.
> Does this mean, the damage to our recorder is severe and we will have
> to live with high parity errors? In any case, we will try your
> suggestion of adjusting the 2nd-head parameters by hand as well. Do
> you determine this parameter by manuaaly "peaking" on a track that was
> recorded using the 2nd stcak ?

Normally when you use "label" for a tape then the FS will recognize
if it is thick or thin by looking at a list of known labels
(like VLBAxxxxx , SVLBIxxxx ,USNOTxxx are thin but USNO0xxx, EVN0xxxx
are thick, etc.) Then the vacuum is set, for a triple-cap head, to
9-10" for thin and 15" for thick. Then thin/thick operation is
possible. If vacuum is set to same value for thick and thin then
temporary degradation would result, but not real damage.
I think these thick/thin vacuum parameters have moved to a
new file (drivev1.ctl) in 9.4.117 upwards.
The procedure to check calibration of the read head is
to set both heads e.g. to stack=-330,-330,F,F (both offsets
for forwards direction), write something using the "normal" head,
rewind, turn off record, then play back on the other head.
If you look at the output on a 'scope you will see
the recorded waveform. Do "peak=10", making sure that replay volts
is not >10 . The picture on the 'scope may get bigger, if it does
do "stack" to find the new head position and hence the offset.
Expect an offset of 5-10 microns. The forward/reverse offset
should not need fiddling.
>
> Another query now. On 15th and 16th of August, we have two bits
> of test times on the telecope for VLBI. The first of these will be used
> to run a test with three VLBA antennas + GBT. The second one is unplanned
> yet. We were wondering if we could run a two-station test with Eb on
> that day. Is it too late to arrange such a thing. If not, do we need to
> contact somebody else ? The UT range avaiable here is:
>
> August 16: 21 UT --- August 17: 00 UT

The antenna is doing a fairly long session of 0.9mm at that time,
at least during local nighttime. Daytimes are mostly free, and
could be used e.g. for 6cm.
On the other hand if the weather is bad on 16th/17th it might
be possible, then also 18cm possible. And the summer has been
fairly wet this year - it rained on St. Swithin's day (ask Chris).
Perhaps you ought to contact Rolf Schwartz, the scheduler
(rschwartz@mpifr-bonn.mpg.de), mentioning I would be available to do
observations if he schedules them.

regards, dave