Demodulating Receiver

Posted on Feb 7, 2014

The Demodulating Receiver (A3017) contains a 902 ’930 MHz 30-dB amplifier, a downshifer, a 60-dB 50-MHz limiting IF amplifier, a frequency discriminator, and an amplitude demodulator. The A301701A circuit board also includes, just for good measure, more copies of the A3016SO SAW Oscillator and the A3008C Spectrometer. If you can`t understand our

Demodulating Receiver
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terminology (RF, IF, LO, dB, dBm, etc), please consult our Terminology page. [FEB-07] Below you see the A3017A RF Amplifier layout next to its predecessor, the A3016DR RF Amplifier. The former amplifier worked well: 27-dB of stable gain from the RF input to the IF output after the mixer and IF low-pass filter. Consult the A3016DR manual for measurements of the RF passband. The new, unmodified amplifier, as shown below, oscillates. It`s not the missing capacitors around L201 that stopped oscillation in the previous amplifier. As we describe here, we replaced these capacitors with solder lumps in the previous amplifier, and it was stable. We applied copper tape, cut tracks, changed resistors, and soldered wire links. So far as we can tell, the problem is the loop closed by our +15 V power tracks. In the previous layout, +15 V came up through the ground plane in two separate places for the two amplifier stages. In this layout, +15 V comes up through the same ground plane penetration. The figure below shows our solution for the A3017A, which is the version we use in the A3018A and A3018B ). Figure: Modification to RF Amplifier Layout for A3017A. We use two rectangles of copper tape to stop oscillations, one 55 mm G— 13 mm the other 10 mm G— 19 mm. [05-AUG-10] We built three more A3017As using a new batch of ERA-3SM amplifiers. These have slightly different markings. Despite rectangles of copper tape as shown above, the RF...

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