Today it’s time to give a presentation about the receiver’s front end. When testing this one with an interfrequency of 9785 kHz I suddenly encountered that I had a strange demodulation phenomenon due to a very strong broadcasting station inside the if channel. After some days of listening and trying to decipher the words in English language I recognized that the „jammer“ was Radio Romania International transmitting on 9783 kHz. OK, folks, right beside the if-channel. Front end selectivity was the problem.
After conceiving about this problem, the conclusion that I drew was that with a receiver front end of only 2 tuned circuits the problem could not be solved to satisfy my demands on receiver purity. But a circuit of 3 LCs should do. So this solved the problem finally. So, here is the circuit of front end, rf preamp and first mixer:
Peter Rachow (DK7IH): The 20 Meter/14MHz SSB tranceiver: The receiver’s first stages
The circuit on the transceiver’s veroboard:
Peter Rachow (DK7IH): The 20 Meter/14MHz SSB tranceiver: The receiver’s first stages on board
C u soon! 73! De Peter (DK7IH)
Today I’d like to present my new homemade 14-MHZ-SSB-Transceiver to my fellow radio amateurs. Some basic information should be given first before details and circuits are to be discussed:
Frequency range: 14,000 kHz to 14,350 kHz
Transmit power: 15 to 20 Watts max.
Mode: SSB only.
The main units of this transceiver are:
- SSB-Generator: LM358 operational amplifier as microfone amplifier and MC1496 Gilbert-cell mixer for signal production.
- TX-Mixer: MC1496
- Transmitter consisting of 4 stages: 1 preamplifier, 1 predriver, 1 driver, 1 final (push-pull), all equipped with bipolar transistors
- Receiver: single conversion, interfrequency 9.785 MHz, 1 rf preamplifier (dual gate MOSFET) followd by mixer (dual gate MOSFET), SSB-filter, if-pre and if-main-amplifier (MC1350), product detector (CA3028A), audio preamp, audio final amp (LM 386)
- Frequency generation: DDS with ATMega32 driving an AD 9835
- S-Meter and AGC-circuitry: ATMega8 driving led-chain for S and RF presentation an r2r-network with op for generating agc voltage.
SSB Transceiver for 14 Mhz (20mtr) by Peter Rachow (DK7IH) – Block diagram
SSB Transceiver for 14 Mhz (20mtr) by Peter Rachow (DK7IH) – Front view (OK, it’s not 100% QRP… 😉 )
SSB Transceiver for 14 Mhz (20mtr) by Peter Rachow (DK7IH) – Interior view
To be continued…
(C) 2014 by Peter Rachow, DK7IH