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RF Diode Detector Measurements

Diode Power Output

201.png 301.png Power sweeps for the two Schottky diode detectors, 201S (left) and 301S (right). The sweeps were performed with three different input impedances. Lower load impedances give a quicker rise time but reduce the amplitude of the signal. The lowest amplitude/fastest rise time signals here are achieved with a 150$\Omega$ load impedance.
Power sweeps with the same load impedances as before for the tunnel diode, KDT6018. Again, the 150$\Omega$ load impedance gives the quickest rise time and lowest signal.

Signal Attenuation

The maximum input power for the Schottky diodes is 17dBm and is 14dBm for the tunnel diode. Depending on the cavity and the beam parameters, the signals expected from the pickup may exceed these levels. As such, attenuation will need to be added before the diodes.

position.png mono.png

The table below shows the expected signal and necessary attenuation for both pickup cavities for a few different beam offsets and charges. The output of the position cavity is linear with offset and charge and the reference cavity output is linear with charge, so it is easy to estimate expected signals and using the table it is possible to estimate necessary attenuation.

Cavity Offset Bunch charge Signal Voltage Schottky Attenuation Tunnel Attenuation
Position 1nm 100pC 2.9$\mu$V - -
1$\mu$m 50pC 1.5mV
100 pC 2.9mV
1mm 2.9V 2.2dB 5.2dB
Reference - 50pC 6.5V 9.3dB 12.3dB
100pC 13V 15.3dB 18.3dB

Amplified Signal

A prototype amplifier has been built which theoretically should give a gain of 1.8 (can be doubled if necessary), this has been verified in the lab. The plot below shows the amplified output voltage for each diode.


The 6018 diode saturates very early and the 2 Schottky diodes are very similar. The 301S was chosen to be used on the reference cavity spare port because it offers a slightly larger output than the 201S. The reference cavity was chosen as it's signal is expected to be larger than the position cavity, thus avoiding the non linearity seen at the lowest input signals. It was installed with 20 dB attenuation.

Amplifier Test

The 3 amplifiers were tested using the same method above for the 301S.


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Topic revision: r6 - 06 Jun 2013 - JackTowler

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