Hi all,
I recently took a sneak peek in the RF world of black magic and pixie dust..
What I made is a device (two devices I suppose..) for my old man. The sensor part can monitor temperature, humidity and water level, in his greenhouse, which is then transmitted to another device that prints the information out on an LCD display.
The thing works and im pretty happy with it. But im not so sure about this waveguide I made.
Not knowing much RF stuff, I just went with off the shelf components. What im using are two SX1272 LoRa transciever modules from Semtech, link down below. Working at 868 MHz, which is an open frequency here in Europe. The antenna output is going through my waveguide into the SMA connector, into the coax cable and out into my external antenna.
http://www.farnell.com/datasheets/2162976.pdf
http://dk.farnell.com/te-connectivi...ial-sma-straight-jack-50ohm/dp/1248990?st=sma
http://dk.farnell.com/lprs/rg174-150mm/cable-rg174-150mm/dp/2096227?st=sma
http://dk.farnell.com/lprs/ant-ss900/antenna-stub-straight-868-915mhz/dp/2096218?ost=2096218&ddkey=http:da-DK/Element14_Denmark/search
So, 50 ohm output, into 50 ohm transmission line, into 50 ohm connector, into 50 ohm cable, into 50 ohm antenna. That's how it should be, as far as I read..
Not much to this schematic, but adding it so it's out of the way. A1 is the SMA connector ofcourse..
PCB layout. Ground plane on both top and bottom.
Topside of etched PCB
Think I traced the waveguide on the wrong side. I soldered that SMA connector on the top, seems it's supposed to connect on the bottom instead, woooops...
Now, anyway.
I got the trace width and ground plane distance by playing around with the values on this site: http://chemandy.com/calculators/coplanar-waveguide-with-ground-calculator.htm
Here was my results. Not 50 Ohm exactly, but pretty close I think, I had to be able to actually etch it too..
The PCB was some stuff we had at work, 1.5mm thickness, it said 4.1 ER on the package. So, assumed that was it.
The width of the gap it seems was this. I made that 0.25mm
So far so good I think? Feel free to murder me if it's wrong at this point.
But to my actual question. What really bugs me is, nowhere I look, does it seem to specify a length of the trace, or care about the frequency been used. Am I missing something? Or does this simply not matter.. I would love to know if this is correct, I dont have the equipment to actually verify the signal strength and losses.
Hope you guys can sort me out as always.
Best Regards
I recently took a sneak peek in the RF world of black magic and pixie dust..
What I made is a device (two devices I suppose..) for my old man. The sensor part can monitor temperature, humidity and water level, in his greenhouse, which is then transmitted to another device that prints the information out on an LCD display.
The thing works and im pretty happy with it. But im not so sure about this waveguide I made.
Not knowing much RF stuff, I just went with off the shelf components. What im using are two SX1272 LoRa transciever modules from Semtech, link down below. Working at 868 MHz, which is an open frequency here in Europe. The antenna output is going through my waveguide into the SMA connector, into the coax cable and out into my external antenna.
http://www.farnell.com/datasheets/2162976.pdf
http://dk.farnell.com/te-connectivi...ial-sma-straight-jack-50ohm/dp/1248990?st=sma
http://dk.farnell.com/lprs/rg174-150mm/cable-rg174-150mm/dp/2096227?st=sma
http://dk.farnell.com/lprs/ant-ss900/antenna-stub-straight-868-915mhz/dp/2096218?ost=2096218&ddkey=http:da-DK/Element14_Denmark/search
So, 50 ohm output, into 50 ohm transmission line, into 50 ohm connector, into 50 ohm cable, into 50 ohm antenna. That's how it should be, as far as I read..
Not much to this schematic, but adding it so it's out of the way. A1 is the SMA connector ofcourse..
PCB layout. Ground plane on both top and bottom.
Topside of etched PCB
Think I traced the waveguide on the wrong side. I soldered that SMA connector on the top, seems it's supposed to connect on the bottom instead, woooops...
Now, anyway.
I got the trace width and ground plane distance by playing around with the values on this site: http://chemandy.com/calculators/coplanar-waveguide-with-ground-calculator.htm
Here was my results. Not 50 Ohm exactly, but pretty close I think, I had to be able to actually etch it too..
The PCB was some stuff we had at work, 1.5mm thickness, it said 4.1 ER on the package. So, assumed that was it.
The width of the gap it seems was this. I made that 0.25mm
So far so good I think? Feel free to murder me if it's wrong at this point.
But to my actual question. What really bugs me is, nowhere I look, does it seem to specify a length of the trace, or care about the frequency been used. Am I missing something? Or does this simply not matter.. I would love to know if this is correct, I dont have the equipment to actually verify the signal strength and losses.
Hope you guys can sort me out as always.
Best Regards