Just to clarify for the inquiring minds... 10km & 20km optics tend to have the same TX power, but 20km have better RX sensitivity.
There is a fair amount of variance by MFG in specs, and also variance in individual optics out of the same batch. So stuff that is TX with less than 1db of power, you should be perfectly fine.. but stuff that is TX with more then 1db of power, then you should attenuate to make sure you are getting about a -3 on RX. Faisal Imtiaz Snappy Internet & Telecom 7266 SW 48 Street Miami, FL 33155 Tel: 305 663 5518 x 232 Help-desk: (305)663-5518 Option 2 or Email: supp...@snappytelecom.net > From: "George Skorup" <geo...@cbcast.com> > To: af@afmug.com > Sent: Wednesday, September 14, 2016 9:55:22 PM > Subject: Re: [AFMUG] Single mode attenuators needed at 30m > I use the MikroTik and FS 20km SFPs with short patch cables all the time. > Nothing bad has happened yet. DDM reports the Rx power around -6dBm, but you > can't always trust the DDM data, however I highly doubt they're overloaded. > Then we have customers at about 2-4 miles usually around -9 to -11. When the > contractor doesn't screw up anyway. Had a couple at -21 and they still worked. > Not even any errors with traffic load. > I agree completely, buy a light meter. > On 9/14/2016 8:16 PM, Faisal Imtiaz wrote: >> My humble suggestion:- >> invest in a light meter. not need to guess.. >> Get a $50 unit from FS.com or amazon... they are not junk, and get the job >> done. >> Standard optics (SMF) 10km should be fine with shorter cables. >> LR (Long Range) 40K or up... you can have them overload the receiver... >> A tip shared from the field.... >> Keep an #2 pencil handy.... if you need to make an attenuation in a hurry >> !... >> take the fiber cable and start warping it around the pencil as tightly as you >> can .. >> and tape it so that it does not unwind. >> I have tested this .... using a light meter... and yes it does work, you may >> need to give it 15 or more turns.... >> BTW those optics putting out 4db those are meant to light up 40km or 60km >> links.. but are also used in link where there is lots of loss expected due to >> Mux/Demux or other passive device.. >> and yes you don't want to use these with a short cables :) >> Faisal Imtiaz >> Snappy Internet & Telecom >> 7266 SW 48 Street >> Miami, FL 33155 >> Tel: 305 663 5518 x 232 >> Help-desk: (305)663-5518 Option 2 or Email: supp...@snappytelecom.net >>> From: "trey" <t...@3dsc.co> >>> To: af@afmug.com >>> Sent: Wednesday, September 14, 2016 7:08:55 PM >>> Subject: Re: [AFMUG] Single mode attenuators needed at 30m >>> You should not need any attenuation if you are using the same lr sfp/xfp on >>> both >>> ends. However there is a small chance if they are different part numbers or >>> manufacturers that one may transmit at the same or greater than the others >>> max >>> receive level. Typically it is a .5-1db tx with a max rx of 3-4. I have ran >>> into some 4db tx XFPs though. It will probably work fine like that, but I >>> have >>> had a couple trickle errors under high utilization. >>> I would say it's always best to keep some attenuators on hand probably 5db >>> and >>> 10db with those you can make just about any optic work at any distance less >>> than what they are rated. I personally carry around everything from 1-20db >>> because of manualy balancing dwdm systems and seem to go through 4,7 and 13s >>> the most. >>> -------- Original message -------- >>> From: Chuck McCown <ch...@wbmfg.com> >>> Date: 9/14/16 5:19 PM (GMT-06:00) >>> To: af@afmug.com >>> Subject: Re: [AFMUG] Single mode attenuators needed at 30m >>> The SFP spec will have an absolute maximum RX level. If I remember >>> correctly, >>> last one I checked was higher than the max TX level of 4 dBm. Seems like the >>> absolute max RX was something like 16 or 20 dBm. >>> From: Eric Kuhnke >>> Sent: Wednesday, September 14, 2016 2:41 PM >>> To: af@afmug.com >>> Subject: Re: [AFMUG] Single mode attenuators needed at 30m >>> Those are totally safe to use with even a 1 meter fiber patch cable between >>> two >>> pieces of gear in the same rack. >>> On Wed, Sep 14, 2016 at 1:39 PM, TJ Trout < t...@voltbb.com > wrote: >>>> 1310 10gb 10km >>>> On Wed, Sep 14, 2016 at 1:38 PM, Eric Kuhnke < eric.kuh...@gmail.com > >>>> wrote: >>>>> What frequency and tx power of singlemode? You do not need to attenuate >>>>> 1GbE >>>>> 1310nm LX (5-10km reach) or 10GbE 1310nm LX optics for very short >>>>> distances. >>>>> Tons of ISPs use all 1310/LX optics for intra-rack and intra-suite fiber >>>>> XCs >>>>> because they're cheap, easy and multimode is dumb. >>>>> If you are using optics which are marketed as capable of 20, 40 or more >>>>> km reach >>>>> (and/or 1490nm, 1550nm optics) you do need to attenuate on the Rx. >>>>> On Wed, Sep 14, 2016 at 11:20 AM, TJ Trout < t...@voltbb.com > wrote: >>>>>> Do I need to pad my optics at 100ft? Or could someone tell me how to >>>>>> estimate >>>>>> the loss so I can compare to the spec?
