# HG changeset patch # User Mychaela Falconia # Date 1539192177 0 # Node ID 1dbc8c5d9698863300e1755ca63862c76596068d # Parent 4f873ec004f69d86cff3c8ed0daf4faa2e66da23 FCDEV3B-repackaging: triband vs. quadband section added diff -r 4f873ec004f6 -r 1dbc8c5d9698 FCDEV3B-repackaging --- a/FCDEV3B-repackaging Wed Oct 10 16:33:11 2018 +0000 +++ b/FCDEV3B-repackaging Wed Oct 10 17:22:57 2018 +0000 @@ -181,3 +181,50 @@ The above approach would provide a usable digital voice interface that would be completely transparent (invisible) to the Calypso DSP and even to the ARM-side firmware, hence it should work without any nasty surprises. + +Triband vs. quadband +==================== + +One shortcoming of our current FreeCalypso modem solution is that it is triband +and not quadband; more specifically our standard hw build omits the GSM850 band, +or we can build a different configuration that supports GSM850 but omits EGSM +(the 900 MHz band). To the best of our knowledge the GSM850 band is used very +little these days, but being only triband makes us look bad compared to the +competition: all of the mainstream proprietary GSM modem modules are fully +quadband these days. + +It *is* possible to make a Calypso-based quadband modem, as TI had one: their +Leonardo reference board for the Calypso+Iota+Rita chipset existed in several +versions some of which were quadband, and their E-Sample board (Calypso+) which +used the same Rita RF block was also quadband. However, changing our current +FC modem design from triband to quadband would involve a highly invasive PCB +layout change: basically our entire modem PCB layout and particularly the GHz RF +section would have to be ripped up and reshuffled into a different arrangement. +Furthermore, if we as the FreeCalypso community do decide that we wish to +produce a quadband modem, I (Mother Mychaela) would NOT be comfortable with +entrusting the needed re-layout work to an "ordinary" PCB layout contractor who +is not a cellphone RF design expert, instead we would need to get a consultation +from an RF PCB design expert who has experience very specifically with GSM +cellphone design and not any other applications. Finding such an expert would +be a major task in itself, and that expert most certainly won't come cheap. +Therefore, a quadband FreeCalypso modem probably won't happen unless we get +someone with a lot of money to throw around. + +There is one exception, though: if anyone would like to see our FreeCalypso +modem repackaged into the SMT module form factor copied from BenQ M32 and pays +for that venture, the result would be naturally quadband as the layout of BenQ's +module follows the same floorplan in the RF section as TI's quadband Leonardo +and E-Sample layout. However, that approach would involve a step to reverse- +engineer BenQ's layout by slicing their board and imaging its inner layers, +hence anyone seeking this approach would need to be prepared to pay for that +step. + +If anyone ever does pay for the creation of a quadband version of our +FreeCalypso modem solution, be it in BenQ's physical form factor or some other, +this quadband modem will need a different firmware build configuration: there +is no way to have the same fw image work on both triband and quadband modems +given that the RFFE control signals are different, and there would be no way for +the fw to autodetect which hw it is running on. But all of the other design +guidelines listed above should still be followed, so we can have only two fw +build configurations (triband and quadband) without an explosion of further +build variants for different GPIO wiring and whatnot.