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Topic: Battery and antenna for MKR GSM 1400 (Read 963 times) previous topic - next topic

rhttu

Nov 19, 2018, 05:32 pm Last Edit: Nov 19, 2018, 05:36 pm by rhttu
I am trying to get a MKR GSM 1400 deployed to a remote environment. I have had good results thus far in my code, but I think I've reached the point where my GSM.begin methods are not returning AT+CREG results (0,0) and I feel it may be due to the reception strength. It may be time to power the unit with a little more juice other than just running from the USB port. The signal may not be the only issue, but I need to start considering the deployment configuration in the meantime.

I have been shopping around for two devices, a battery and an antenna, and these are what I had in mind and what my questions are.

Battery - https://www.adafruit.com/product/328
On the Tech Specs section of the Arduino site, there is an asterisk on the "Supported Battery(*)" section. In this case, the board supports a 3.7V LiPo, which is what the aforementioned battery is. However, at full charge, this battery specifies up to 4.2V output. I am particularly interested in this asterisk now because I don't want to exceed the battery voltage output rating, but I don't see anything further describing this asterisk, or if this voltage would be safe!

Antenna -
I will probably purchase an RP-SMA adapter going to a high-gain omnidirectional antenna since I will not have control over the setup and calibration of the antenna at its deployment location. The manufacturer spec sheets specifies using a 2dB stock antenna onboard the unit. Another factor I can't seem to find in the documentation is external gain limitation. I realize this will be dependent on my battery, but wasn't sure if there were any upstream considerations re the ampacity of the physical etchings or other circuits that might restrict (or worse, destroy) the board when using a high power antenna.

Thanks!

ballscrewbob

LiPo's do have a charged voltage a little higher than the stated 3.3 volts for the board but the circuitry is there to handle that from the LiPo connector. I am sure the designers were aware of the battery specifications. They can actually reach 4.7 volts on some LiPo's.
3.7 volts is I think a NOMINAL voltage.

There should not be any issues with a better antenna and the actual gain of that.
Caveat would be POWERED / ACTIVE antennas or Amplifiers which I would avoid for a deployment that could saturate the front end of the receive side unless it was designed properly (so probably not an active Chinese one)

Am awaiting delivery of a similar arrangement myself as you are not the only one  to notice the stock unit is a little low on signal. (probably great for most users)
It may not be the answer you were looking for but its the one I am giving based on either experience, educated guess, google or the fact that you gave nothing to go with in the first place so I used my wonky crystal ball.

rhttu

Thanks for the information. That is good to know. Out of curiosity, is there a particular antenna you're planning on using or have had luck with? I think most cell phones have about a 4-6 dBi gain strip configuration, and we generally get okay reception in this area. I have not tested AT&T in the area, however, and may need to compensate a bit more.

ballscrewbob

#3
Nov 19, 2018, 09:21 pm Last Edit: Nov 19, 2018, 09:23 pm by ballscrewbob
I ordered one of these



And the suitable adaptor.
Will be sitting it on top of a coffee can as the ground plane. which should suffice as the coil is quite low.
Supposed to be around 7-9 dBi
Also means I can stuff everything inside the can for outside placement ;)

Also ordered a YAGI to but thats just to play with.
You said you dont need to go that path but it is the better option for forward gain if you know where to point it and it doesn't need a ground plane.

It may not be the answer you were looking for but its the one I am giving based on either experience, educated guess, google or the fact that you gave nothing to go with in the first place so I used my wonky crystal ball.

rhttu

Cool. I'm still figuring out what antenna I need, as I don't have a lot of knowledge in that realm, which is why I asked.

I don't know what frequency my carrier will attempt to use. I am assuming 850MHz for now as a US rural spec for CALA regional deployment. Datasheet of 1400 says 433/868/915 MHz, but I'd imagine that's broad and not region specific.

ballscrewbob

#5
Nov 19, 2018, 10:02 pm Last Edit: Nov 19, 2018, 10:02 pm by ballscrewbob
The carriers are usually NOT county or state specific but COUNTRY specific with most now covering the same freq. bands to allow consumers to travel with thier phones.

This should help out.


It may not be the answer you were looking for but its the one I am giving based on either experience, educated guess, google or the fact that you gave nothing to go with in the first place so I used my wonky crystal ball.

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