QUESTIONS ABOUT THE OPERATION OF MY RAM SYSTEM

RAM-10000 Systems

Q. Why isn't there any output from the "High Power RF Pulse Out" BNC connector?

A. First, please check if the high-voltage rectifier fuse has opened. Most often, this is due to a transistor failure in the gated amplifier module, typically resulting from the loss of any load on the gated amplifier output. Sometimes, however, the rectifier fuses become brittle and can open due to mechanical shock not an electrical problem. The fast-blow rectifier fuse is located in the round fuse holder on the rear panel of the RAM-10000. Typically, this fuse is a Bussman GBB-8 8 ampere 250V fast-blow rectifier fuse; older systems may have the GBB-6 6 ampere fuse. Please replace the fuse with the similar kind. Slow-blow or standard fuses should not be used as replacements because they will not provide adequate protection. If there is still no output after replacing the fuse, or if the fuse is still operational, please check if the trigger has not been accidentally programmed to computer trigger or external trigger. This can be identified by looking with the oscilloscope to see if there is a signal at the "Trigger Out" BNC connector at the rear panel.

Q. Why isn't there a trigger output from the rear panel?

A. In order for the timing module to produce a trigger output and the necessary gates to turn on the gated amplifier, a continuous wave (CW) radio frequency (RF) signal must be connected to the "CW In" connector on the module. If for some reason, the synthesizer has stopped operating or the CW amplitude is too small, then the timing module will not operate correctly and there will not be an output trigger from the RAM-10000. In Mark I and Mark II systems, the source of the CW signal is an external synthesizer, whose output is connected to the "CW In" connector on the rear panel of the RAM instrument. In Mark III and Mark IV systems, the CW signal is generated in the synthesizer module with a nominal peak-to-peak amplitude of 1V. In Mark VI systems, the CW signal at the desired operating frequency is generated by mixing the output from the synthesizer (fsynthesizer = foperating+freference = foperating +25 MHz) with the 25 MHz reference signal (freference) in the phase detector module to generate (fsynthesizer + freference= foperating+50 MHz) and (fsynthesizer - freference = foperating). A filter is used to select the difference frequency. This signal is then sent to both the gated amplifier and the timing module with a nominal amplitude of 0.5V peak-to-peak when the output of the phase detector is connected into both the timing module and the gated amplifier module.

Q. Why isn't the high power RF burst coherent with the external trigger input signal?

A. This delay is due to the timing circuitry generating the gates, which are used to select the desired number of cycles from the CW RF signal and to turn on the gated amplifier. The gates turn on at the positive zero crossing of the RF CW signal and are on for a programmed number of RF cycles. If the external trigger is sent just after a zero crossing, then the circuitry will wait until the next zero crossing before starting the high-power RF burst. Therefore, there can be an uncertainty of up to 1 period of the operating frequency between the external trigger input and the start of the high-power RF burst. The "Trigger Out" signal is always coherent with the start of the RF burst.

Q. I would like to digitize the received RF signal from the RAM-10000 Mark IV or Mark VI system. Is there a method to permit multiple signals to be averaged?

A. Digitizing the received broadband RF signal can be done on a single-shot basis by using the "Trigger Out" from the RAM-10000 as the trigger for the digitizing card. This will eliminate the uncertainty in the start of the high-power RF burst. While this technique can be used to acquire multiple signals of the received waveforms, there will be some uncertainty in the digitization process due to the different clocks in the RAM-10000 and the digitizing card. To eliminate this uncertainty, it will be necessary to use a common clock for the RAM-10000 and the digitizing card. In some systems, we have modified the RAM-10000 to bring out the clock.