Re: [AFMUG] Help me Grok this - tolerance to reflected power

Thu, 21 Aug 2025 12:01:12 -0700

Rub it on your dhirt.
Sent from my iPhone

On Aug 21, 2025, at 12:15 PM, Ken Hohhof <[email protected]> wrote:



And only sissies use those cleaning pens, spit works just fine, right?

 

From: AF <[email protected]> On Behalf Of castarritt
Sent: Thursday, August 21, 2025 12:39 PM
To: AnimalFarm Microwave Users Group <[email protected]>
Subject: Re: [AFMUG] Help me Grok this - tolerance to reflected power

 

For PON specifically, I think you can run into interferrence issues from bad connections with inadequate return loss long before you have to worry about damaging the transceivers.  That's why everyone uses APC connectors for PON.

 

On Thu, Aug 21, 2025 at 12:20 PM Adam Moffett <[email protected]> wrote:

It's PON, so yeah Bi-directional.  Different wavelengths for each direction.

 

From: AF <[email protected]> on behalf of Ken Hohhof <[email protected]>
Sent: Thursday, August 21, 2025 1:08 PM
To: 'AnimalFarm Microwave Users Group' <[email protected]>
Subject: Re: [AFMUG] Help me Grok this - tolerance to reflected power

 

I assume this is not BiDi fiber?

 

From: AF <[email protected]> On Behalf Of Adam Moffett
Sent: Thursday, August 21, 2025 12:01 PM
To: AnimalFarm Microwave Users Group <[email protected]>
Subject: Re: [AFMUG] Help me Grok this - tolerance to reflected power

 

I think the "tolerance to reflected power" was the wrong direction to look.  That seems like it's more about not damaging the equipment. I'll back out of the rabbit hole and just ask what I'm trying to figure out:

 

How much does reflectance actually hurt you on PON?  Google results are vague.  

 

Example: You generally need to have two connectors at the OLT (device to patch panel), and there's one connector at the ONT.  If you fusion spliced everything else so there were no additional reflective events, would there be a measurable BER or stability difference compared to having a coupler in the NID, connectorized splitters in the field, etc.

 

Another example: An AFL Fastconnect twist-on SC/APC field termination has -50dB reflectance according to the spec sheet.  A factory terminated connector or splice-on connector is -65dB.  How much does the twist-on hurt you?

 

 

-Adam

 

 

From: Adam Moffett <[email protected]>
Sent: Thursday, August 21, 2025 11:54 AM
To: AnimalFarm Microwave Users Group <[email protected]>
Subject: Help me Grok this - tolerance to reflected power

 

 

Definition from ITU G.987:

3.3.15 tolerance to reflected power (transmitter): A transmitter parameter that characterizes the

maximum admissible ratio of the average reflected optical transmit power incident at the transmitter

to the average optical transmit power. 

 

If my average transmit power is +6dBm and the tolerance to reflected power is -15dB, then 6 - 15 = -9, so reflected power as strong as -9dBm won't harm the transmitter?  

Is it that easy or am I misunderstanding the definition?

 

-Adam

 

 

 

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