The HDR-2005 is a simple homebrew HF receiver for approximate 100 kHz to 30 MHz. It is a direct conversion receiver with an I/Q quadrature sampling detector, phase shift (polyphase) network, AF filters, AF AGC and AF amplifier. At the front end there are an attenuator, a band switched BPF and a switchable HF preamplifier.
50 Ohm antennae input. Simple protection circuit and switched attenuator. Relay-switched BPF. Optional switchable HF preamplifier (2N5109).
30 MHz LPF (Amidon T50-2). Double balanced quadrature sampling detector (FST 3253, 4 x 68n caps). PreAmplifier (2 x INA163) with
GainControl (3 steps: 20, 40, 55 dB).
One disadvantage of this quadrature detector is a proper impedance matching on the RF side. In the HDR-2005 I use for
this reason a 1:4 transformation (Balun) and a "50 Ohm anchor" (this attenuator caused a little change for the worse of the
noise figure, but I think its necessary for constant matching).
SSB/AM line switch (HEF4053). Active polyphase network (4 x NE5532). Sideband demodulation (1/2 NE5532). 3.5 khZ LPF (1/2 NE5532). Switched capacitor BPF 250 Hz - 3 kHz (2 x LMF100). Passive 3.5 kHz LPF (with real LC). Simple AM demodulation and active 10 kHz LPF (TL074).
AGC (OTA LM13700, TL0x). AF amplifier (TDA2009)
100 MHz Master oscillator. DDS (AD9951). 120 MHz LPF, Post-DDS-Amplifier (ADA-4543). Quadrature modul (74VHC132, 74VHC86, 74VHC74).
ATMEL AVR ATmega8515 uC, 4x4 KeyPad, 2x16 LCD, Rotary Encoder (Old Stepper Motor). Firmware with BASCOM.
Traditional Main-PowerSupply (+5V, -5V, +12V, -12V) and DDS-PowerSupply (+3.3V, 1.8V, 1.8V)
