Hello FC community, Today I picked up the 850 MHz FreeRunner which I bought just before New Year and started examining it. First I read out its Calypso NOR flash and examined its FFS - the factory calibration performed by OM looks the way I expected it to, just like the more common tri900 version, but with the 850 MHz band calibrated and the 900 MHz band left uncalibrated, i.e., the opposite of the tri900 config. The Rx and Tx calchan subbands are exactly the same as what our own fc-rfcal-tools create, based on TI's LoCosto calibration document.
The OM-calibrated GMagic number for the GSM850 band is 202 - it means that the GSM850 band Rx path is no worse than its 900 MHz sibling on the tri900 version in terms of the insertion loss. Then I disassembled the case, extracted the motherboard+display set, then removed the WLAN daughterboard and the shieldcan cover over the GSM section. At first visual inspection everything looks the same as in the more common tri900 version: 3 Rx band SAW filters after the antenna switch that look the same to the naked eye, and the population of the "RF magic glue" components between the SAW filters and the Rita transceiver's LNA inputs is also the same as in the tri900 version: series inductors at L401-L406, while the shunt capacitor footprints C405-C410 are left unpopulated just like in tri900. The following remain to be determined: * The main part: some time in the next few days I will take this deshielded tri850 GTA02 motherboard to the hardware lab at my day job and use the powerful microscope there to read the part number marking on what should be the GSM850 downlink band SAW filter at U402. * The series inductors at L401 and L402: are they the same 7.5 nH value as in the tri900 version, or different? Depending on what the SAW filter part number turns out to be, we may or may not need to measure the L401 and L402 values on this OM tri850 specimen. If the SAW filter is a B7845 or equivalent in terms of the expected output impedance like I suspect it to be (matching B7820 in the tri900 version), then the simplest course of action will be to buy some B7845 parts from the same wonderful Chinese folks from whom I got all of our current Calypso+RF components, put one of them on an FCDEV3B, and measure the resulting Rx path performance with the CMU200 - will we get the same good GMagic as OM's without changing L401 and L402, or not? We shall know more as soon as I get an opportunity to look at the deshielded tri850 GTA02 MB under a good microscope - stay tuned! Hasta la Victoria, Siempre, Mychaela aka The Mother _______________________________________________ Community mailing list Community@freecalypso.org https://www.freecalypso.org/mailman/listinfo/community