11

Normally, the WWLAN testing and debug is done in electromagnetically shielded cages in labs when external tower signals (or local 3G-4G repeaters/re-translators) are too strong. The tests are usually done with special instruments like Agilent LTE tester, which has all abilities to change signal levels and simulate weak reception. In normal operation the LTE ...


9

To "simulate" a poorer cell reception you can use RF attenuators between your board and the antenna. They are composed of multiples resistances building a network that will attenuate RF power very predictably, both in RX and TX, while maintaining the proposer RF impedance as seen from the modem and antenna. They have a limited power rating. Do not run your ...


5

Looks like you are using an active GPS antenna which certainly means it has a LNA built-in. If you are setting-up the modem in GSM mode, at higher transmit power (if I recall correctly can go up to +30dBm) you may eventually damage the LNA output stage and therefore not get anything out of your GPS antenna. It does seem like an unlikely scenario though, you ...


5

RF is tricky. I wouldn't mess with the antenna, I think the product should be tested in its final configuration. The reason for this is simple: when reception is really bad, your transmitter will increase its power to its maximum value, and you WILL be interested in knowing if the (rather enormous) amounts of RF it will crank out will crash your micro, ...


4

I got some help from an Aeris engineer with this one. It turns out that when a SIM first registers with the network, it requires better signal quality than subsequent registrations. When the SIM has successfully registered with the network the first time, some information is stored on the SIM that allows it to register easier the next time. Mobile phones ...


3

The usual equipment for this kind of test includes Spectrum analyzer. A spectrum analyzer will be much more sensitive than an oscilloscope for detecting sinusoidal RF signals. Anechoic chamber, or at least a Faraday cage. To ensure you measure only signals from the DUT, not from other devices nearby. Calibrated source and antenna. To cover current cell ...


3

Bad reception can not only stem from low signal, but also from the distance to the cell tower. Especially GSM is only designed to go over about 35km. Otherwise the "timing advance" between sender and receiver of the RF signal would be too large for the protocol in use. See https://en.wikipedia.org/wiki/GSM and other resource for more information about that....


2

Some possibilities: Connect the antenna to a dummy load Use a step attenuator between the antenna and the radio using double shielded coax Conduct your experiments in a shielded room / enclosure Note that a proper attenuator is not a simple resistor. It consists of a resistive pad that has impedance matched inputs and outputs. Look up T pad resistive ...


2

Simcom has discontinued the Temperature readout for cost down reasons. The diodes in the module which are required for temperature readout are no longer assembled. The feature was not useful anyway, as the module heats up especially when charging the battery, so the readout way alway way above the ambient temperature.


2

My question is I can pour ground copper on my first layer with via fencing and stitching at a distance of wavelength/20. Should I keep the ground pour separate for LoRa, GPS and LTE module? There are a few problems with separating ground planes: Return currents on the ground plane have to travel back to the source via a different pathway (usually). If ...


2

The currents will be constrained to the area under the transmission line. You can just pour one copper. In addition they are in separate bands so even if they do interfere it will not necessarily give issues (After all, the antennas themselves will interfere anyways). The most important thing is to have good uncut grounds under the transmission line. I ...


2

The width of the stripline is not a design target in itself. You design a transmission line to have a specific impedance, to match the antenna or whatever is at the other end of the transmission line (or both, if possible). So, you're right to calculate based on your actual substrate and copper properties. Both 1.3 and 0.3 mm are feasible widths, and ...


2

Asynchronous serial communications places demands on the accuracy of the clock. Some internal calibrated RC oscillators are acceptable, some are not, and some are okay over a limited temperature/Vcc range and/or if you don't have additional errors due to divider resolution (typically at higher speeds). The receiving party starts timing the data based on ...


2

If you use your favorite search engine and search for terms like "nb iot roaming" you'll find plenty of other pages backing this. I'd interpret this (2017) document from the GSMA in a way that it says "NB IoT specifations have been written very quickly, Roaming might be added later" https://www.gsma.com/iot/wp-content/uploads/2017/08/CLP.28-v1.0.pdf This ...


2

It seems that somehow your "replacement of wire" has caused a situation where the received signal is partly being sent back or being coupled onto your microphone circuit. Possibly both receiver and microphone wires are running adjacent without any shielding. At the least you should use twisted pair for these wires. If you pay attention to this aspect, ...


1

I contacted a testing lab and they explained several details to me. I do need radio certification. This certification is called IC (Industry Canada). I should use a cellular module in my product that already has radio certification. This way I can leverage their certification (provided I use an antenna with the same or less gain and keep the device above ...


1

Neil's answer is good, but I'll add a couple more points that might affect your choice of geometry There are good empirical formulas available (and online calculators that implement those formulas) for choosing microstrip trace width to achieve a desired characteristic impedance. The online calculators for coplanar are more likely to disagree with each ...


1

'Better' and 'most efficient' are not words that are useful to use. Both microstrip and coplanar have their own advantages and disadvantages. However, often it's the integration with the significant ICs on the board that's the key factor. Some ICs have pinouts that invite connection directly to coplanar (with a GND-sig-GND set of pins) or microstrip (with a ...


1

Yes, of course it does. It is fundamental to the whole cell phone concept that the system needs to know where to route an incoming call, and in order to keep the location database up to date, the phones must periodically ping the nearest towers. This has been true from the very beginning.


1

Some GSM systems have tiny on-the-wall cell-sites, thus the "distance" might be just a meter (about 10 wavelengths). The pathloss will be 22dB + 10db*log10( [distance/wavelength]^2 ) or 22 + 20 = 42dB pathloss. This comes from the geometry of energy spreading out, with spherical behavior around the antenna, and 1/range^2 dropoff in energy density. Now ...


1

It seems the version of the SIM800 Series User Manual that I posted above from Adafruit (v1.09) is out of date. The newer version v1.10 from simcomm2m.com mysteriously has the AT+CMTE? command removed. I guess that is SIMCom's subtle way of saying this command doesn't work.


1

This is a great article for you on the subject based on Part 15 of Title 47 CFR. I do not have a huge experience on this but when I have dealt with parts that are part of an assembly, such sub assembly was not tested. Why? for example the same board would be use in multiple chassis each one having a different EMI signature and shielding. Also differences in ...


1

In theory yes, but in practice no. Besides the firmware, the hardware in the client device is usually set to communicate on only a few frequencies and the transmitter is limited to the uplink frequencies while the receiver circuitry is limited to the downlink frequencies for noise suppression and other reasons. One would have to change the filter circuits, ...


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