I developed a device that can be mounted inside a waste container. The device is battery-powered with an expected lifespan of about 2 years and publishes hourly data. It is designed to monitor the following things:
Container collections by the truck
The fill-rate of waste inside the container (i.e. 0% is empty, 100% is full)
Temperature (for potential fires)
I'm also working on adding a camera that will send images OTA, but this isn't implemented yet
My issue: I have been testing 15 units of this device (image 1) for a while now - while it works, for a few locations the connectivity is excessively poor. These locations are in populated urban areas however with several cell towers nearby, so good connectivity should be possible. My theory is that the poor connectivity is caused by bad device design, such as:
(most likely) poor antenna placement, with metal inside the device causing interference
(potentially) using the wrong data carrier for my simcards
I tried tackling the antenna placement issue, but would greatly appreciate additional feedback.
image 1: current device setup
My current device features a uFL PC104 antenna glued onto the PCB. The PCB has double-layer GND plane underneath the antenna - I'm aware this is pretty bad design.
image 2: prospective device setup
In my prospective design I will:
Use an SMA TG 22.0112 antenna located at right side of the enclosure away from metal parts
Partially run the antenna trace trough the PCB to avoid having to run a long cable
Move the battery further to the left (away from the antenna)
A large area of the PCB GND plane will be removed underneath the antenna
Note:
The devices go on metal brackets and are mounted inside metal containers (exception: the lid). These factors can't be changed.
My questions:
(1) For image 1, am I right in that the amount of metal around the antenna is excessive and this has a big effect on connectivity?
(2) For image 2, are there any improvements I'm forgetting about that could improve the connectivity more?
Except for the ones which require a ground plane, of course.
It is obviously do-able. Cellphones have metal in them and no protruding antenna. But you can't answer the question by just looking at a photo. This requires dedicated simulation software. Or lots of testing.
The obvious question is why have you not tested the various options for the layouts to see which one is the most effective for radiated field ? With the right equipment and knowledge this is easy enough.
We can all guess as to what might 'help' but you cannot use guesses to replace basic testing.
Looks like a commercial design, so pay an RF engineer to sort it out ?
Wawa:
Big mistake. Antennas must have NO metal nearby.
Leo..
On image 2, the closest metal would be the battery, which is .250'' away and only partially borders the SMA antenna. Is the antenna far away enough from metal in this image? The way the device is mounted inside the container (almost upside-down), the signal would actually travel through the PCB.
srnet:
The layout looks very poor.
The obvious question is why have you not tested the various options for the layouts to see which one is the most effective for radiated field ? With the right equipment and knowledge this is easy enough.
We can all guess as to what might 'help' but you cannot use guesses to replace basic testing.
Looks like a commercial design, so pay an RF engineer to sort it out ?
I agree the layout is horrible - I'm very new to this kind of stuff (no electronics/engineering background whatsoever) so I'm learning every day. I may consider having a professional engineer work this out, as I don't have any equipment myself to test this.
srnet:
Consider it ? Do you have any alternative ?.
So if this is a bit of commercial\Professional equipment, why not employ someone to sort it out ?
In the past I ran a successful test with about 40 devices using the Taoglas PC104 antenna. Since then, I added a lot of new components to my design (including the large battery + 2 ultrasonic sensors) which is affecting the signal a lot. But I belief if I can sufficiently separate the metal away from the antenna again, the devices may be restored to their original performance connectivity-wise.
Hiring an engineer for it also would be very expensive, and with my exceptionally bad initial design I don't think it's a bad move to first do one proper design (costing almost nothing) to see if issues persist.
srnet:
Could be, but that is what you should expect if your running a business, is it not ?
I'm not running a business - I'm doing this as a side-gig to my current job. My company made a small budget available to try out a few IOT things, but with the quotes I've seen for PCB antenna design, I likely would not have the budget for it unless I can show there's no way it can be done otherwise.
Hence why I first want to give a different antenna placement a shot. It wouldn't cost much, and if connectivity is still poor it'd strengthen the case to involve engineers in the antenna development.
This is a highly specialized area - one bordering on magic. To get the most you will need a specialist. One where impedance matching is super important.
This is a highly specialized area - one bordering on magic. To get the most you will need a specialist. One where impedance matching is super important.
wolframore:
here's your problem... the metal containers are blocking RF. You will have to solve that.
I respectfully disagree - there's dozens of companies in this industry that develop IOT-devices, and all go inside the exact same container and connect just fine. I also ran a test with 40 devices a while ago in metal containers, and I had few connectivity issues.
The main factor that changed between then and now is that I added the large battery and several metal components. I assume since the containers have plastic lids, there's still a large enough window for the RF to travel through.
BTW - I can't see any of your pictures... so unfortunately I'm flying blind.
OK - if it can be done then it can be done... perhaps they design the placement so the reflections don't cancel each other out and create nodes... not sure. Again a specialist can give you all the details
So how about a large box for your project. One that allows you to put the battery next to the PCB and well away from your antenna instead of on top of it. That should at least get the big chunks of metal away from your PCB antenna, more or less restoring the original design that you said actually worked.
Maybe you don't get the maximum possible transmission, but as long as what you get is good enough it's good enough.
By the way, it'd be great of you at least had linked to your other thread on what seems to be the exact same project. I do believe info given there, especially details such as the containers having a plastic lid, could be quite important.
