Hi Alan:
I have had a chance to do a detailed read of the proposed
VSI-H spec dated
11 May 2000. It looks very good to me--I especially
like the mechanism that
has been chosen for synchronization of the DOM to the
DPS. It looks very solid
to
me. I just want to point out two things that have come
up in my work on a
proposed correlator and digital phasing system for the
Expansion VLA:
1. GORE makes an 80-pin MDR cable that could be used
for the VSI-H. The cost
for each cable is a few hundred dollars but it is capable of
better than 1 Gbps
on each 40 twin-ax lines up to several meters in
length. Each twin-ax cable is
individually shielded and jacketed. We use these
twin-ax cables in our current
correlator at 1 Gbps--although not in the 80-pin MDR format.
2. The digital phasing subsystem we are proposing for
the EVLA could produce
data at sample rates up to 256 Ms/s (128 MHz
bandwidth). Is it possible to
include this rate in the VSI-H as an option? Or,
better yet, allow rates > 128
Ms/s in doubling factors. Otherwise, some
demultiplexing of data onto the bit
streams would be required. If the GORE cable is used
it could certainly
support the 256 Ms/s bit rate. Note that the digital
phasing subsystem would
allow rates lower than 256 Ms/s to be generated if
necessary.
Good work on the specification and, "I approve"
the spec.
Cheers,
Brent Carlson
DRAO--Penticton.
PS the GORE web site is:
and the cable is known as "MAX-BAND". I
don't believe the web-site shows the
MDR-80 pin cable but I have gotten a quote from the
manufacturer: they only
make 80 pin and 100 pin "MAX-BAND" cable with the
MDR connectors.
"Alan R. Whitney" wrote:
> Gentlemen,
> -
> I have received recent e-mails from Dick Ferris and
Kondo-san (for the
> Kashima group) indicating their approval of the
proposed VSI-H
> specification dated 11 May 2000 and distributed to you
on 11 May
> 2000. Does silence from the other VSI committee
members indicate approval
> also?! I would much appreciate even a single word
e-mail from each member
> of the VSI committee indicating approval or disapproval
(presumably
> accompanied by constructive comments) so that we can
complete the VSI-H
> effort. I will plan to distribute the final
VSI-H spec at the end of this
> week unless there is some major problem.
> -
> Note: This e-mail is being sent only to the formal
members of the VSI
> committee, though please distribute as you like.
> -
> Many thanks,
> Alan
> -
> ------------------------------------------------
> From Dick Ferris (14 May 2000):
> -
> Hi Alan,
> -
> That looks fine.
> -
> Nothing to note but a couple of typos.
> p.1 TOC "15. Glossary"
> The two sections are now 15.1 and 15.2
> p.9 footnote 3
> ""... footnote *in* Section 13.4"
> p.17 Section 12.3, item #1
> a stray "f" at the end of the line.
> -
> Recently someone mentioned that a candidate cable was
shown to the
> Haystack meeting. I suspect it may have been from the
MkIV
> correlator. Do you have a part number for it?
> -
> Cheers,
> Dick
> ------------------------------------------------
> For completeness, here is Will's reply to Dick's cable
question:
> -
> Hi Dick,
> -
> In your recent e-mail, you referred to a cable that was
shown at the
> Haystack meeting. The following information applies to
that cable which is
> used in the Sub-Millimeter Array (not Mark IV).
> -
> The cable is custom made by 3M with 80 pin MDR
connectors on each end. The
> connectors are molded to the cable sheath to provide
strain relief. The
> part number is OM-90101G-080-N4-472.4. It is 472.4
inches in length (12
> meters). In March of 1997, the SMA project bought 25 of
these cables for a
> total cost of $5067.50, so they are about $200 apiece.
You can find a
> description of the cable at
> http://www.mmm.com/Interconnects/apl_cas_foil.html.
In the SMA project, the
> cable is driven with differential ECL signals at a
clock rate of 52 MHz.
> -
> Regards, Will
> -
> ------------------------------------------------
> From Kashima (22 May 2000):
> -
> Dear Alan,
> -
> We, Kashima VLBI group read the final draft carefully
> and we concluded that i t seems to be OK.
> -
> Best regards,
> Tetsuro Kondo + Kashima VLBI group