|*() labeled for second connector name|
**each shield is independent without unit 16/17
|Fig.1 Flat cable.||Fig.2 ID1 cable||Fig.3 ID1 & VSI|
VLBI data transfer had been using differential ECL signals and twisted pair cables. Figure 1 shows typical cable and an example of shielded cable. Figure 2 shows ID-1 connector and cables used in Japanese K-4 VLBI. The assembled cable is also consist from twisted pairs and an assembly shield. These cables are enough performance below 32MHz rate. But above the 32MHz and multi vendor environment expected in the VSI, exact ECL signal shape must be maintained between the unit. The IVS-TDC CRL group experienced parallel 128MHz ECL data transfer will cause terrible degrade and error with slight cable difference. We strongly propose to employ twisted pairs with shielded each for 64MHz expansion. Although this will increase the weight of cables, the de-fact standard cable as in Fig.3, the assembly employed AWG27 equivalent conductor is attractive size (15mm diameter) and reasonable price ($50/meter). If a special cable is designed for VSI, it will drastically increase the price and difficult to obtain replacement one. As for the connector, The connector shell and connector latch mechanizm expected be have stiffness to support the cable weight. The D-sub with screw bolt is the most preferred for the purpose. VLBI equipment are connected and disconnected very often on site. But If a top grade brand is employed less troubles are expected. Also it important the on site engineer can inspect signals directly. Although others are small and attractive, it is better to employ D-sub 50 for the VLBI purpose. The succeeded Japanese 1024Mbps VLBI system uses four ID1(256Mbps) cables currently. This is very confusing in cable connection work. We will adapt our interface to the VSI standard when they are determined.
Below 32MHz rate, it is possible to introduce another signal by special wiring as in Table2. This needs special wiring and not recommended.
|* shields are partially common|
Fig.4 D-sub50 wiring in a shell.
Panel cross section
|High speed long|
|Price in Akihabara||Application,|
|D-sub||65x14||YES||$12-$20||HDTV. Good reputation and long history. Price dynamic range. D-sub 25 is very popular and matured. Easy to check signal on site.|
|52x11||Unknown,Latch seems poor to support shielded cable weight||$10||SCSI, no long history.|
|80x15||YES||$15||Printer, computer,Share decreased. due to huge connector size and repeatability.|
|40x10||Unknown,Latch seems poor to support shielded cable weight||$18||SCSI|
|95x11|| ||$15||VME, cable connector available.|
|68x6||Latch poor to support shielded cable weight||$5||Computers, very popular cheap. Expensive discrete wiring.|