CW QRP TRANSCEIVER MULTIBAND

Here's a weekend project for the homemaker.

Here I'd like to introduce you my latest version of a neat and easy to make homebrew 4-bander CW QRP transceiver for the homemaker. The design is based on a classic DC receiver and a class C transmitter.

I made the VFO from an Analog Devices AD9850 DDS module which is the heart of this tiny multibander. These DDS modules are usually available for less than 15 US$ / € at Ali, Amazon or ebay.

The AF amplifier following the 74HC4066 mixer consists of a pair of NPN BJTs which forms the low noise pre-amplifier, a single TL084 quad op-amp for amplification and filtering and a JFET for RX/TX-mute. This in my opinion is some kind of a minimum of semiconductor components for making a well working shortwave DC amateur radio receiver. Although both sidebands are received I found that this isn't a real drawback.

A classic LM386 audio power amplifier driving a small loudspeaker or headphones. Be careful with high audio levels because this DC receiver offers no automatic gain control (AGC). High audio levels may enter the headphones which might end in an painful experience. To avoid this a good as possible 2 antiparallel diodes are connected to an amplifier stage of the TL084.

The front-end mixer is made from a 74HC4066 CMOS switch. This mixer is so good that almost no additional filters are required between antenna and mixer input. However, I added a 3 MHz high pass filter as a precaution to keep strong noises below the filter's cutoff frequency away from the receiver input.

DDS AD9850 MODULE

DISPLAY 0,96" SSD1306 I²C

ATMEGA328P MICRO

Features:

+ AD9850 DDS generator module
+ Microchip ATMEGA328P-PU, 16/20 MHz
+ Rotary encoder for frequency and menu
+ 9k6 RS232 Remote Control, Kenwood system
+ QSK with frequency shift and RX mute
+ Microcontroller sidetone generator
+ Automatic CQ call, also with CQ loop
+ CQ loop contest mode
+ Setup of your individual callsign for CQ
+ CW Filter fix for 700 Hz center frequency
+ PC Remote Control, Kenwood TS-480 standard
+ Receiver RIT for split mode operation
+ Relative signal strengh display
+ Battery voltage display
+ I2C OLED display 128x64
+ smooth working IAMBIC keyer WpM 5 to 50
+ Single lever, straight key option
+ Bug key simulation option
+ Output power 5 Watts, MOSFET
+ Elliptic LPF, 80&60 plus 40&30 mtr band

Alignment:
There's almost no alignment necessary. The receiver's performance greatly depends on the DDS variable resistor's tuning. This variable resistor matches the necessary 180 degree phase shift of the two DDS output signals into the 74HC4066 mixer. An oscilloscope would be a great helper, though you may tune this for best receive performance with a small screw driver.

DDS AD9850 PCB ENTER SERIAL MODE PROGRAMMING
The AD9850 by default is in parallel mode which is set by the factory. However, as soon as the microcontroller has successfully sent the first data packet in serial mode to the AD9850 DDS, which can be easily checked with a monitor receiver, the DDS oscillator remains in serial mode, as long as the RESET line is connected to GND. This is very important to check!

The datasheet stated that the data lines D3 and D4 must be switched to VCC and the data line D2 to GND, but apparently this statement in the datasheet is not correct. The AD9850 apparently automatically enters serial mode once it has successfully received serial data in the correct sequence.

Some pre-assembled AD9850 PCBs available on the Internet do not have the RESET line connected to GND. Check this if you aren't sure about the RESET pin GND connection.

RF LOWPASS FILTERS:
These filters have an input and output impedance of 50 ohms. I recommend Cauer elliptic filters for sufficient harmonic suppression. See the table below for examples.
On the photos you can see that I do not use cores with the identification color red (T-50-2). Of course you can do it that way. T37 cores should just work without heating up too much. However, there is still some room for experimentation here. Please email me if you have any suggestions for improvement. The table shown here is just an example.

AF BANDPASS FILTER:
I like it when the CW signal I'm interested in is boosted, but the environment around the frequency still remains a little audible. If you prefer a sharp CW filter than there's plenty room for experiments.

The picture below shows the frequency response made from a noise generator, plotted by a SDR software.
Note: dB scaling here is only relative.

QRP TRANSCEIVER CW FILTER

PC REMOTE CONTROL:
The transceiver partially emulates the Kenwood TS-480 PC remote control. The RS232 speed is 9600 baud, 8N1. I have tested the remote control with several PC ham radio software like CQRLOG, DXLab and others. However, I haven't implemented every KENWOOD command, so I can't guarantee that it works with every available PC software.

Click here for download: FIRMWARE ZIP FILE
Clock speed is set to 20 MHz.
Latest: MARCH 31, 2023 V 1.0.12

Upload ATMEGA328P hex files in a Arduino environment with software xloader

https://github.com/binaryupdates/xLoader

Please send me an e-mail if you have any questions about the project. dl6zb@dl6zb.de

<<< BACK <<<

	Short Press	Long Press
<ENC>	TX ZERO BEAT	MENU
<WpM>	CW SPEED / WORDS PER MINUTE	AUTO CQ
<ENC> + <WpM>	QSO MODE: Auto CQ Loop, 10 times CQ, spacing 10 seconds CONTEST MODE: Auto CQ loop, 10 x, spacing 2 seconds


	The receiver is housed in the tinplate enclosure, which is concealed beneath the transmitter and low-pass filters. The transmitter with the output stage transistor is mounted on top of the tinplate case. Behind it are the two low pass filters for 80/60 and 40/30 meters. On the right side are the DDS and the microprocessor.