high-quality 2.3 GHz Amateur Radio Transceiver

Posted on Feb 6, 2014

The receiver is a tripple superheterodyne receiver with two PLL-guided local oscillators. The first LO (2. 1 GHz) can be set in steps of 500kHz and sets the RX signal down to 188 - 188. 5 MHz. It has a high PLL loop bandwidth of around 20kHz, therefore gives low phase noise of below -80dBc/Hz at 1kHz from the carrier. (=> very high S/N-ratio on the

high-quality 2.3 GHz Amateur Radio Transceiver
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audio output, providing the received signal is strong enough. The second LO can be tuned from 177. 3 to 177. 9 MHz and sets the signal further down to 10. 7 MHz. The VCO is very carefully design and exhibits -87dBc/Hz at 1kHz phase noise. Due to the low noise of the VCO itself a small loop bandwitdh of 70Hz can be used and therefore a step width of 2. 5 kHz is possible. FM-demodulation is performed at 455kHz using a NE614 baseband IC that has a very good RSSI output to drive the S-Meter (up to 80dB dynamics, giving 50mV per dB). High quality Murata IF filters are used for channel filtering. A LM386 audio amplifier is used to drive the loudspeaker. The first mixer is a image-reject mixer (UAA2077), negleting the need for a narrow input-filter to attenuate the image frequency. This makes it possible to tune over a wide frequency range with constant sensitivity. While the UAA2077 is made for frequencys up to 2. 0 GHz (the american PCS cellphone system), it still give 28dB image rejection at 2. 3 GHz if a carefull layout and good grounding is used. In front of the first mixer is a very low noise amplifier with a noise figure of 1. 5dB and a gain of 22dB. It includes a mild band-pass-filter to make sure that the maximum gain is achived at 2. 3GHz. Frequencys below a few hundred MHz are strongly attenuated to avoid overloading the next stages with strong VHF broadcast signal, cellphone signals, man made noise etc. The image...

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