[TriEmbed] wireless communications and battery life

Pete Soper pete at soper.us
Wed Jan 8 11:11:01 CST 2020


About a year ago I was forced to deal with a use case for a 900Mhz 
transceiver putting roughly 20mW that called for it to be inside an 
aluminum beer tap handle. It was astonishing how well it worked, with a 
range of a couple dozen feet. But it had a large hole in the end, and it 
was driving a full size dipole antenna, not the little chip antennas or 
zig/zag PCB quarter waves the folks on this list are likely to be 
using.  A closed metal mailbox would pretty much guarantee frustration.

-Pete AD4L

On 1/8/20 11:33 AM, Brian via TriEmbed wrote:
> On 1/7/20 10:43 PM, Glen Smith via TriEmbed wrote:
>> I'll add my welcome to Brian's, and add a +1 to most everything he said.
>>
>> The only additional insight I hope to add would be that you may very 
>> well be able to add a small solar cell to the top of your mailbox 
>
> Great idea!  And very likely the complete answer to the power 
> question, since the device will only be awake a tiny fraction of the 
> day, as you pointed out.
>
>>
>> You biggest problem may be transmitting through the Faraday cage of 
>> the mailbox.
>>
>
> Faraday cages aren't very effective when they aren't grounded.  If the 
> mailbox doesn't have continuity to Earth (on a dried-out wooden post, 
> maybe), it won't attenuate the signal as badly (RF power will still be 
> lost by induced eddy currents in the metal, but the metal won't be as 
> reflective as it would be if grounded).
>
> That said, all you really have to do is get the antenna outside the 
> box.  It shouldn't be too hard to find an Arduino-friendly RF module 
> with a connector (SMA or UFL) instead of an onboard antenna; then a 
> short cable and "rubber duck" antenna mounted outside the box is all 
> you need.
>
> -B
>



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