Tower Top Amplifier Troubleshooting

TTA Troubleshoot _Jim

TTA – Mechanical Assembly

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TTA – Debug/Troubleshoot

Tower Top Amplifier ATE Test Equipment (top to bottom): ARB RF Signal Generator RF Power Meter, DMM Spectrum Analyzer RF I/F Drawer (relays, couplers, Noise Diode, Bias Tee, etc) UUT Test Shelf RF (10.7 MHz) Signal Generator* PC* with GPIB card and Data Acquisition Card, etc FAN Power Supply UUT Power Supply (* Located under shelf/not visible)

TTA Manufacturing Tests • Q23 DC Bias Tuning o Voltage measured across a .025 Ohm Resistor o Good practice to verify Gate voltage of Driver stage while cover is off!

• Parametric ‘testing’: o o o o o o

Check/Adjust TX Gain, freq response, Measure dynamic performance (ACP and/or Mask) Check TX time domain (Ton/Toff) Check RX frequency response Measure RX NF (Noise Figure) Check RX time domain (Ton/Toff)

Sample Test Data Sheet

Sample Test Data Sheet, Zoomed

Troubleshooting • DC Current Consumption on +24V Input o For RX mode and TX mode respectively

• Power Supply voltages o +24V input voltage; present through to switchers? o +8V, Switcher – also provides Vdd for driver o +5V, Linear o -5V, Charge Pump – FET bias voltages o +28V, Switcher - Vdd for PA

Troubleshooting • RF Switch control lines o Make sure right switches (including PIN diodes) are on and off for proper TX/RX state o Make sure 10.7 MHz detector and amps operating correctly

• Measure voltages on active devices o Some devices’ current consumption can be measured via a series resistor to Vdd pin

Troubleshooting • RF Matching and Filter networks (low pass, high pass filters) must have correct components or parameters like RX NF and Reflection Power Trip will show anomalous, unexplained fails – RX NF value increases of any losses in front of LNA FETs – TX Reflection Power Trip trips ‘lower’ due to any ‘mismatches’ in output circuit past circulator

TTA - Troubleshoot

TTA - Troubleshoot

TTA Troubleshooting - RF Probing

• Stage-by-Stage measurement of RF Gain • Usually the step of ‘last resort’ when the problem has not yet been found • Example of RF probing the RX chain follows using a simple Signal Generator and Spectrum Analyzer

RX – RF signal at Input

RX – Input Signal Strength (-49.33 dBm)

RX – Output of LNA Stage

RX – SS after LNA (-46.35 dBm)

RX – After Filter/AMP

RX – Signal Strength (-16.14 dBm)

RX – After Step Attenuator

RX – SS Aft Step Atten (-15.99 dBm)

RX – Output

RX – SS at Output (+0.38 dBm)

RX – Gain Stack up example • • • • •

SS Level -------------Input -49.3 dBm After LNA -45.3 dBm After Filt -16.1 dBm After Step Att -15.99 dBm Output 0.38 dBm

Gain ------------n/a 4 dB indicated* 33.2 dB 33.3 dB 49.7 dB

*Note: Probe loading can and does affect SS reading.

Fin