[Make-wifi-fast] 2.4Ghz hybrid wiring for nest protects

Bob McMahon bob.mcmahon at broadcom.com
Wed May 19 00:47:06 EDT 2021

Thanks, this helps. Yeah, looking for "better than nothing" here for sure.
I also gotta watch out for taking on liabilities myself. Disclaimers of no
responsibility will need to be clear.

I'm not understanding the connecting pairs together in your response.

I was thinking of a single directional antenna per floor connected into a
2.4Ghz Wilkinson power divider with 22 dB isolation for the splits going to
adjacent floors. This way each floor would reach one floor up and one floor
down and no further. (I haven't yet measured the power outputs of the
devices and of a heavily trafficked 2.4Ghz noise floor to make sure 22dB is
sufficient.) I'd connect the bottom floor to the top floor the same way so
basically each floor has one peer up and one peer down.

|--> (3dB less per power split) to floor above
Fire alarm (free space)  Ant--->PD (0.5dB loss) |
                                         -- 22dB isolation between

|--> (3dB less per power split) to floor below

where PD is a Wilkinson power divider, 5 floors for 5 PDs.

Then the LMR connects the Wilkinson's splits to each other. The LMR is
external to the building (along the rear ladder) and the antennas internal.

The floor logical topology becomes 5<-1<->2<->3<->4<->5->1 such that any
single hop failure only impacts that floor. Passive materials will be
military grade, hermetically sealed and inside conduit. The building has
two sets of egress stairs so alerting per one set being compromised can
direct to the other. The internal stairwell is connected floor to floor -
that was required by the fire department (and was costly to the owners.)

I was hoping to be able monitor the devices' topology and detect
any changes using remote servers in the cloud. So far no luck in getting
that information via an API that I can find. I think this is a critical
piece, i.e. having always on servers bugging someone to pay attention to an
unexpected topology change or a need for battery replacements.

I don't think there'd be fire marshal approval for this but, even without
that, I think this meets the "better than nothing" goal and isn't
prohibitively expensive.


On Tue, May 18, 2021 at 5:09 PM David Lang <david at lang.hm> wrote:

> passive repeaters (two antennas connected together with no electronics)
> work
> much better than most people realize.
> I would do floor-by-floor antenna pairs, and if each device going off
> should
> trigger the one on the next floor, I'd consider spacing them out so that
> you
> don't have one antenna pair feeding a strong signal to the next pair.
> If the only purpose of this is to relay the fire alarm signals, use
> high-gain,
> narrow beamwidth antennas pointed at the alarms, this will do wonders at
> overcoming the general noise on 2.4GHz
> I have too much radio experience to be happy trusting anything wireless
> for
> critical things, but where the alternative is no connectivity, it's better
> than
> nothing.
> David Lang

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