| T.R | Title | User | Personal
Name | Date | Lines |
|---|
| 119.1 | min distance = 0 | HGOVC::RAYMONDSIU | | Thu Aug 23 1990 05:35 | 3 |
| According to DEFCN & DEFEB, there is no minimum distance.
Rgds,
|
| 119.2 | 1 km is min. for 100 micron fiber | NSCRUE::KNIGHT | | Thu Oct 18 1990 18:54 | 13 |
| In "DECconcentrator 500 Problem Solving" (EK-DEFCN-PS), section 1.4.1, there is
a note:
Lengths less than 1 kilometer (3280 feet) of 100 micron fiber do not have
sufficient optical loss; malfunctions of the receiver can occur. Use
62.5/125 patch cords to induce loss.
I did not find a similar note for the DEFEB, but it presumably should have the
same caveat.
Regards,
Paul Knight
|
| 119.3 | No minimum length for multimode PMD for ANY fiber | KONING::KONING | NI1D @FN42eq | Mon Oct 29 1990 18:05 | 15 |
| I have no idea where the statement quoted in .2 comes from. It certainly
is incorrect.
This is obvious from the fact that you can use loopback connectors to
connect transmitter directly to receiver. Those have near-zero loss,
and work correctly. Since fiber, even 100 �m fiber, has loss, not gain,
it follows that there is no minimum length.
Another way to tell is by looking at the FDDI PMD standard, which shows
the maximum optical power for both transmitter and receiver as -14 dBm.
(Note that the above applies to multimode optics, which is what our current
products have.)
paul
|
| 119.4 | minimum distance for 100�m fiber is valid | BAGELS::LEVY | | Tue Oct 30 1990 17:58 | 78 |
| re: .3
Paul's analysis proceeds from an incorrect assumption: That is, DEC
FDDI MM optics launch no more than -14 dBm into 100�m fiber.
The assumption is incorrect. Testing has documented a potential launch
power increase of 1.5 dB, to -12.5 dBm, which can over-saturate an FDDI
receiver. [See extract from Chris Baldwin memo, at end.]
The 1 km minimum distance for 100 �m fiber is a safe demarcation point
for guaranteeing a minimum loss without the use of 62.5/125 patch
cables.
.2's observation is valid. We need to add the note to the DEFEB Problem
Solving guide. Note that the DECconnect Fiber Optic Installation
manual, page 7-14, correctly calls out a minimum loss, and specifies
using 62.5/125 patch cables to achieve it.
Jon
+---------------------------+
! ! ! ! ! ! ! ! INTEROFFICE MEMORANDUM
! d ! i ! g ! i ! t ! a ! l !
! ! ! ! ! ! ! !
+---------------------------+
TO:Distribution: DATE:7/28/89
FROM:Christopher Baldwin
DEPT:CSE Technology: Fiber Optics
EXT:227-3637
LOC:TAY2-2/N15
NODE:GIGA::BALDWIN
SUBJECT:Supportable Transmission Distances for FDDI Physical
Connections Using Alternate Fiber Sizes.
.
.
.
2. 100/140 Cableplants:
3 HP Transceivers and Sumitomo transmitters were tested
for transmitter optical launch power increase. The NA of
the fiber was 0.29. A 1.5 dB increase was found.
The receiver was found to have a 0.5 dB vignetting
penalty when used with 100 um core fiber. The penalty
was confirmed for worst case mode scrambled conditions (
mode scramble exit conditions ensure that the light is
maximally distributed throughout the core of the fiber so
that maximum vignetting will occur.) HP explained that
the source of the vignetting occurs at the detector
because the NA and pupil aperture of the focusing optics
is more that sufficient for a 100 um core 1:1 image
relay. The PiN detector is only 90 um in diameter.
While only a 0.5 dB vignetting penalty was found, 1.5 dB
will be reserved for this penalty to account for possible
misalignment between optical relay and PiN detector which
would exacerbate the penalty. The Sumitomo devices were
found to have a 0.3 dB Rx vignetting penalty; since the
difference between the HP and Sumitomo results are minor
the 1.5 dB penalty will be used.
LOSS BUDGET = 11 dB + 1.5 dB Tx gain - 1.5 dB Rx penalty
= 11 dB
NB: The use of 100/140 um patch cords to connect
stations is NOT RECOMMENDED. There is a possibility that
the Tx could saturate a Rx when using a short length of
100/140 fiber. This is currently not a serious concern
as FDDI Connectorized 100/140 cables are a special order
item.
|