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


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.



Brent Carlson



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