[600MRG] Smoke Alarms I

[Kenneth G. Gordon]

On 21 Oct 2014 at 10:25, John Langridge wrote:

> Can we get a detailed clarification on what "not terminated properly"  
> means?

Probably not from me in this case. The reason is that such "termination" is 
completely dependent on what means is being used to connect the various 
parts of the system.

In my experience with early cabled computer-networks, it specifically meant 
that any open connections at the ends of a particular "run" must be 
"terminated" in the characteristic impedance of the line which is being used. 

In the case of the early lines, that was RG-58 or similar, and thus the 
terminators were 50 ohm "dummy loads" installed within a male BNC 
connector.

It also means that when a line is "looped" or "seriesed" through a device, like 
a router or hub, the output connection of that device must have a termination 
on its unused or unconnected output connections in order to prevent 
reflections which would corrupt data.

A completely similar method is often used with in-home TV systems by cable 
from a central amplifier or connection to the TV-cable system: terminators 
must be used on any open ports or at the ends of open lines.

I am certain the principle is identical in the case of hard-wired smoke 
detector systems, but since I am not knowledgeable about those, or how 
they are connected, nor with what, I cannot suggest how to do it.

As someone here suggested, I would think that the thing to do is to go back 
on the installer.

In what I would imagine are low-frequency systems, which those may be, 
leaving lines unterminated would not be noticable to the equipment, but most 
certainly would allow ingress of unwanted RF.

I am sure there must be others here who would know far more about this 
matter than I.

vy 73,

Ken W7EKB