NorCal40A

Project Details

Title: NorCal40A

Class: Electronics for wireless

Semester: Spring 2018

Team: Selasi Etchey, Jeremy Webb, Jiabin Lin

NorCal40A

This is the device that we constructed in Electronics for Wireless class, it can be used to transfer signals to other receivers or and receive signals from other transmitters. This device could be used to transfer the Morse Code, and it works well. NorCa40A is constructed by using different kinds of amplifiers, filters, oscillators, etc. The block diagram for the NorCal40A is shown in figure 1.

Figure 1: Block diagram for the NorCal40A

In the actual construction, we separate the design into eight circuit boards and one mother boards.

Board #5

Board #5 included the transmit filter,

The transmit mixer product both 7.0MHz and 2.8MHz, the difference frequency of 2.8MHz is not very useful, therefore, we need the transmit filter to filter out unnecessary frequencies. Transmit filter's design was shown in the figure 2, since C38 is presetted as 100pF and L6 is presetted as 3.1 µH, the ideal value for C39 should be 68.4pF based on the resonant frequency equation. After making some adjustments, we have our final resonant frequency as 7.1MHz.

Motherboard

The Motherboard covered harmonic filter, transmitter switch,

The harmonic filter is a low-pass ladder filter to decrease the harmonics signals. The design of the harmonic filter is shown in figure 3. Since L7 and L8 is wired by ourselves, our final values for L7 and L8 are 1.29µH based on the measurements.

Board #2

Board #2 included the IF filter. The RF mixer reduces the 7MHz frequency into 4.9MHz by mixing with the signals comes from the VFO oscillator. However, the RF mixer also generates the 9.1MHz frequency, which is useless. This crystal filter is a bandpass filter and has really small bandwidth. The purpose of the IF filter is to filter the 9.1MHz and keep the 4.9MHz. The equivalent circuit of the filter is shown in figure 4.