narrow moon
The Station G2 was unable to hear any nodes other than my personal ones in my house. Adding this filter allows it so exclude nearby cell towers that are amplified by the LNA before they reach it, making the node usable! I can now reach dozens of nodes via a mountain top node over 16 miles away.
dusky narwhal
This is awesome! Any way we could get a guide with the steps on how to do this?
narrow moon
I'm honestly not THAT confident of the work I did here - it's just working. 🙂 I can explain the steps but I wouldn't say I'm the best person to provide a guide. The microscope pictures show where I aligned the part with the traces to know where to scratch off the solder mask. I cut a section of the RF path out where it goes underneath the chip so it had to go through the chip to be connected, being careful to not peel up the trace anywhere it wasn't supposed to be. I then tinned the pads on the part, and on the parts of the board where I scraped away the solder mask. One tip I learned along the way is that the G2 PCB is stacked up with a layer of aluminum between the front cover and the PCB so I was having a hard time getting the groundplane to heat up. I had to remove those layers so I was working with just the PCB to get it hot enough. I used a hot air rework station to heat the area until the solder started to flow, applied a little more flux to the board, then placed the component, careful to orient it so the "input" was toward the antenna connector. Heating the whole area until solder flowed and used tweezers to push it down to ensure contact with the board. I then inspected the input and output connections to make sure there was a solder bead between the traces and the pads on the filter. I had to use an iron to touch up one side that didn't have enough solder to begin with. Then reassemble and test.
narrow moon
I have been asked to do this to another unit so if there are specific steps you're interested in, I can try and take more pictures and get more details.
cinder linden
I have been asked to do this to another unit so if there are specific steps you'...
Details like which filter u used 🤷♀️
narrow moon
Details like which filter u used 🤷♀️
Lol - I pulled it off a cheap SMA 915MHz saw filter I got off aliexpress. I wasn't able to find a datasheet for that specific one.. I'll see if I can provide it for what goes on the next one.
dusky narwhal
That would be awesome, I have a G2 or two laying around and may build the eggs to do this, you know, for science 😅 . Most of our local mesh comprises of Station G2 and we are a large metropolitan area, so if it is something that is worth doing, I may be willing to take a crack at it.
narrow moon
It really seems essential in metro areas.. I have several towers nearby and the G2 was pretty much deaf until I did this. I tried in RX only with the same chip on the SMA carrier it came on and confirmed it helped. I had similar success with a ceramic filter I put connectors on as well but didn't want to take the loss on xmit - this solution seems perfect, like it should be built this way. I know they suggest cavity filters on the wiki but it's a lot of cost, space, and mass and not practical for portable use. It also adds complexity to a tower install I'd rather avoid.
chrome vector
I don't have a G2 to test with but based upon the documentation the LNA amplifies a large frequency range with the peak between 800MHz to 950MHz. In Europe LTE band 8 is 900MHz which would be directly amplified by the LNA. So yeah, a SAW filter specifically tuned to EU868 could really help. Although they do have insertion loss which could effectively counter any gains by the LNA.
narrow moon
Loss of SAW filters is generally going to be less (maybe half) than the LNA benefits, plus it's not just about insertion loss - you're improving the signal to noise ratio. Adding this kind of filter to radios with no LNA can still enable it to receive signals it couldn't before. Because it's more about SNR, not RSSI
spring anchor
Hi, Seems like most of the offered filters on Ali Xpress are rated for 100mW input? The G2 is capable of much higher output.
chrome vector
The filter would be between the RF switch and the LNA so it wouldn't see the TX power just RX. That's one of the big advantages of this board over a module as the modules have the switch built-in so adding a SAW filter to the RFO will see full TX power.
SAW filters are delicate too so it's best to derate them as much as possible. The rating of 100mW is probably for 100% duty cycle and LoRa notes transmit at a maximum of roughly 25% so shouldn't be an issue for a 22dbm (160mW) node. Obviously the G2 can transmit wayy over 160mW.