The objective of this diploma thesis was to develop a practical power amplifier for the amateur radio frequency band at UHF. This ranges from 430 - 440 MHz, though it was extended to 430 - 450 MHz within the context of this thesis. The required amplifier is designed to serve as a secondary level to a hand-held radio. The hand-held radio has an output power of 500mW; the amplifier is intended to increase the output power to 40W, which would improve both the range and the quality of the reception. The amplifier is designed to comply with legal requirements set by BAKOM (Swiss Ministry of Communication). The assignment comprises the development of three components: the actual amplifier , an output filter, as well as the automatic send/receive switch. The fully integrated M57788MR Mitsubishi module was found to have the desired performance for the power amplifier . It is already matched at both the input and output sides. Since the amplifier operates in C mode, this creates harmonics, which have to be eliminated by the output filter. The output filter was implemented with transmission lines as resonators. It primarily consists of two coupled resonant circuits that ensure suppression of the harmonics of at least -60dBc. Since the radio possesses a single antenna port, an additional send/receive switch was necessary. This is designed to switch the output signal to the antenna via the amplifier during radio transmission. The signal should be automatically switched directly from the antenna to the radio during reception. A critical point proved to be the reverse attenuation of the send/receive switch. This has to be sufficiently high enough (approx. 40dB) to prevent the amplifier from oscillating. The result is a fully functional amplifier, which can be employed in the field of amateur radio. Due to the amplifier's wide frequency range (410 - 460MHz), it could also be applied in industrial radio applications.

The idea of our project is to build a broadband scanning-receiver for receiving all frequencies between 100 kHz and 500 MHz. In this band you find all radio- and TV-broadcasting stations as well as all kinds of analog radio applications for example amateur- or aeronautical-radio.

Our system processes the signals to the point where we can use an external demodulator. After receiving the signal from the antenna, it will be filtered and amplified. In the first mixer stage we mix it up to a first intermediate frequency of about 1 GHz. That makes it possible to process the entire desired band with a single local oscillator. In the following mixer stages the signal is successivly downconverted and bandlimited. The output of the 3rd mixer is at 10.7 MHz frequency and that of the 4th mixer at 455 kHz. These are the standard FM respectively AM intermediate frequencies, therefore one can use a normal AM and FM demodulator available on the market.

It is difficult to design a receiver that is sensitive enough for the very weak signals coming from the antenna. These signals can be so weak, that they can hardly be distinguished from the existing noise. The signals need to be amplified in the receiver without increasing the noise by a large amount. When developing the circuits for the system, we payed attention especially on choosing the best possible low-noise parts.

After a few trials all significant modules worked as expected. To build a complete receiver, a user interface and different switchable demodulators for the different modulation types must be built, which we could not do during our project because of lack of time.

The company Elektrobit in Bubikon, Switzerland requires an Oscillator at 5.8 GHz for a future product in connection with the Heavy Vehicle Fee (HVE). Within this degree theses a prototype should be developed, built and tested. Various principles of high frequency oscillators were studied and compared. To fulfill the specifications, particularly the very low phase noise, a Bipolar-Dielectric Resonator Oscillator was chosen. For computer aided High-Frequency-design Microwave-Office was used. With the aid of this software it was possible to simulate the whole circuit and estimate its functionality. In the 3rd starting a prototype could be built up that keeps the specifications reasonably well. The most palpable fault is the wrong oscillation frequency that is 160 MHz too high. By optimisation of the circuit and usage of better components, these problems might be eliminated. In a further step, this oscillator has to be tied to a quartz-reference by a Phase-Locked-Loop (PLL) whereby thermic and mechanical stability should be improved.

For information about this diploma thesis please contact Prof. Ulrich Gysel.