4.2 Transmitter Design
The transmitter card production design incorporates four channels on one PCB, along with the following additions:
- Bias tees for each channel to power the cryo-LNAs
- Sense lines from each bias tee to monitor cryo-LNA voltage and current
- A single calibration signal injection SMP connector with onboard 1:4 splitter
- A single 25 pin micro D-sub connector for +/- 5v power, ground, and cryo-LNA power and sense lines
- A ganged 4 way SMP connector that interfaces with the flexible stripline
- A fixture to hold the four SC/APC fiber connections to mate with a coupler on the I/O plate
The first 4-channel TX card PCBs shown below have been delivered to BYU, are being fabricated, and will soon be under test.
Single Channel Analysis
Single channel versions of the transmit - receive board modules were tested at different attenuation levels and input power levels to ensure linearity. As seen below, the single channel transmit module maintains its spectral response shape over a wide range of variable attenuator levels and input power levels up to about -40 dBm.
Tests were performed at different attenuation levels to show the spectral shape remains the same
Figure 9: TX r3-3 tested at different drive power levels