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→RF Transmitter Circuit
The transmitter RF path contains a filter IC, pi matching network, broadband amplifier, and a few more output filter stages.
[[File:LMS6.png|alt=Schematic diagram|center|frameless|1065x1065px|Basic schematic of TX circuit on LMS6]]
====Low Pass Filters====
Lowpass Filters are included on the output from the PA and CC1050 to filter out spurs and harmonics from the signal. These are required to meet FCC and [https://www.ntia.doc.gov/ NTIA] emissions requirements.
The measurements were taken with a [https://nanorfe.com/nanovna-v2.html NanoVNA V2] and the plots were aquired using the [https://github.com/nanovna/NanoVNA-QT/releases NanoVNA-QT software]. These data should be considered un-calibrated. A S11 calibration OPEN,SHORT was performed on the NanoVNA, but since the coax is cut, I did not perform an S21 calibration. Additionally, the NanoVNA-QT software seemed to blowaway any of the manual settings I had. This software does not seem to support an OPEN/SHORT only calibration. These data can safely be interpreted as realitive measurements, meaning the filter type and cutoff frequency can be determined.
=====PA LPF=====
The PA LPF was measured by removing the DC blocking capacitor after the RF amplifier in the schematic above. The removed DC blocking capacitor is Port 1 of the measurement. Port 2 of the measurment is the antenna output with the antenna removed. The 3 dB cutoff of the filter is 500 MHz.
[[File:LMS6 output lpf 200M-1425M.png|none|thumb|Lowpass filter output from the power amplifier. The blue trace is the S11 plot. The red trace is the S21 plot. This is from 200 MHz to 1.425 GHz. Absolute values are not to be trusted. The relative measurement indicates that the 3 dB cutoff of the filter is around 500 MHz.]]
=====FL101 - CC1050 LPF=====
The FL101 frequency response was measured as shown below. A DC blocking capacitor was removed that was between the output of CC1050 and FL101. Two parallel resistors were removed from the output of FL101. This isolated the filter in the circuit. The cutoff of the filter is 650 MHz.
[[File:FL101.png|none|thumb|Lowpass filter FL101, output from the CC1050. The blue trace is the S11 plot. The red trace is the S21 plot. This is from 200 MHz to 1.425 GHz. Absolute values are not to be trusted. The relative measurement indicates that the 3 dB cutoff of the filter is around 650 MHz.]]
[[File:FL101 test setup.jpg|none|thumb|Test setup for the FL101 measurement.]]
