[TriEmbed] wireless communications and battery life

Rick nm3g at triad.rr.com
Wed Jan 8 17:22:58 CST 2020

Good evening all,

You might consider looking at slot antennas. You can cut the slot in the 
metal surface, connect your feedline, and fill the slot with epoxy and 
paint to suit (non-conductive paint is ideal). Slot antennas have been 
used on aircraft for quite a while and you'll only have to protect the 
coax to slot junction.



On 1/8/2020 12:11 PM, Pete Soper via TriEmbed wrote:
> 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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