SRK Electronics FMA501, Руководство пользователя

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SRK Electronics FMA501 manual
 2007 SRK Electronics Pty Ltd 21
DC voltage proportional to the square root of the input power. This voltage is used by the
control board for measuring the input power.
Returning to the main RF path. The input power is split into two equal parts by the action of
T14, T15 and R20. This is a Wilkinson splitter of classic design.
Amplifier A and amplifier B are identical, so only amplifier A will be described. T12 forms a
balun so the right hand end has two voltages 180° out of phase with each other. The
impedance is stepped down to approximately 6
Ω
by the transmission line transformer formed
by T3 and T4. This is to provide a reasonable match into the gate impedance of Q1. R22-25
and C55,56 ensure stability when driving high Q loads such as cavity filters.
The drain load is transformed back up to 50
Ω by the transmission line transformer formed by
T1 and T2. The balun formed by T9 generates a ground referenced signal once more.
This is then passed into the Wilkinson combiner formed by T16, T17 and R21.
The signal at T10 is thus a nominal 500W, unfiltered.
JP1 and JP2 are high current links which enable tuning of the output filter in isolation. JP2 is
only fitted during factory testing. JP1 is the only link fitted after production testing.
The filter formed by C38-53 and L3-7 ensures that all spurious and harmonic components are
adequately attenuated. This is a 9 pole Chebyshev filter with a minimum stop band
attenuation of 40dB at 175MHz and 60dB at 262.5MHz. Stop band attenuation is better than
60dB at frequencies up to 1GHz.
The filtered RF leaves the palette on J3.
Temperature measurement is provided by the two LM35 temperature sensors mounted near
each transistor. These return the temperature of the copper heat spreader.
6.5
Output directional coupler
The output directional coupler takes the high power RF from the amplifier palette and passes
it to the rear panel. A small sample of the forward and reflected voltages are provide, at
about 30dB down on the main line power.
These voltages are passed to the control board to allow forward and reflected power to be
measured and to ensure the correct operation of the protection functions.
The directional coupler is manufactured using stripline techniques and should not be
disassembled.