TM
FlexRadio Systems 2003 Page 8
Low or no power output on transmit
Operational Description: The SDR-1000 uses a TI OPA2674 (early units used the
OPA2677) Dual Wideband, High Output Current Operational Amplifier for the 1W
driver stage. As stated in the SDR-1000 Hardware Manual, the user should use caution
not to connect the amplifier into unknown or highly reactive loads. An open circuit or
highly capacitive load can cause the circuit to oscillate, resulting in a damaged part.
Also, the circuit requires approximately 0.5Vrms of baseband audio drive on J3 of the
TRX board to reach the full 1W RMS output. Some sound cards may not have sufficient
drive to achieve this level of RF output. The RFE board amplifier has higher gain (as
well as better circuit protection) than the one on the BPF board, thereby allowing full
output with lower level sound cards.
Probable Causes:
1. Low power output in voice modes – Make sure that the RF control on the SDR-
Console is set to maximum (100%). If necessary, engage the Microphone Boost
on the Advanced button of the mixer Record Control panel. This will
significantly increase the microphone channel gain. Make sure that the Wave
control on the Volume Control panel is set to maximum gain. If you still do not
have enough drive, measure the true RMS voltage on the Line/Speaker out
connector on the sound card. Make sure you are able to drive the ~0.5V RMS
level required.
2. Low power in CW mode – The CWControls form on the Visual Basic
SDRConsole has its own “Level” control that sets the RF output in CW mode
only. Its control is independent of the PWR control on the front panel of the
SDRConsole. Make sure this control is set to 100% for full CW output.
3. No output – If an audio signal applied directly to J3 of the TRX board does not
provide any RF output, it is likely that the OPA2674 is damaged and must be
replaced.
Radio Stays in Transmit After Releasing PTT Button
Operational Description: Status line S6 on the parallel port is used to tell the SDR-
Console software that the PTT line has been engaged. The 1K resistor, R9, is intended to
pull the signal line low when the PTT switch is not engaged, sending a high signal to S6.
Probable Causes: The 1K resistor may not provide a low enough impedance to ground
for some parallel ports. The solution is to attach another 1K resistor in parallel with R9
or replace it with a 500-ohm resistor. Newer units may have a 470 ohm resistor installed
already. If you still have problems, you can parallel a 200-270 ohm resistor. The voltage
at R9 should be below 0.6V when PTT is not activated.
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