Amateur radio station since 1993
RA3WDK Homepage





















































































































QRP Project

QRP 20/40 m transceiver

Confirmation DX and 2WAY QRP QSO which has been made by this tranceiver

I like to operate /P/QRP with my portable equipment and antennas.

LZ2KSC / LZ2GX save my signal in QRP contest in 14 MHz



I had many QSO using a simple LW and coax-feed for my 144 MHz yagi.

I use case from FM-301 FM radiostation. IF 500 kHz. PWR 5W (12V) / 8W (13,8V) (RD16HHF1)

Energy performance : RX - 90/120 mA TX - 1,5 A (12V) / 2 A (13,8 V)

    Schematic Circuit Diagram    <<Previous   <№>   Next>>  

Full Schematic Circuit Diagram + modifications


LPF TX, RX BPF, RX mixer, IF amplifier 500 kHz

PA, TX BPF, TX mixer, driver TX, VFO

Power amplifier , RD16HHF1

AF amplifier, CW electronic key, AGC




Low Temperature & High Humidity Test


Modifications for improve Image Rejection ratio for low IF (500 kHz).

The Image Frequency must be removed by BPF, it used ahead of broadband power amplifier.
Alternatively : can used image-rejection mixer could be designed which suppresses one of the input sidebands by phase and amplitude cancellation.
Below see easy idea for simple QRP radio improve Image Rejection ratio to 10-15 db.
For 7 MHz band : Fif(500)=Flo-Frf , Flo=7500-7590 kHz , Frf=7000-7090 kHz , Fimage= 8000-8090 kHz
For 14 MHz band: Fif(500)=Frf-Flo , Flo=13500-13590 kHz , Frf=14000-14090 kHz , Fimage= 13000-13090 kHz

For Q(L)=80 in 14 MHz we have loss in 14 MHz < 7 db and loss in 13 MHz about -45 db

Reject Trap For Q(L)=80 in 7 MHz and 14 MHz, better place for this filter - between stage of driver

Summary work both filters in IF 500 kHz : [500-503 kHz] + [498.5-501.5] = about 1,5 kHz

Modification BPF 14 MHz of RX

Switched-Capacitor AF Filter by MAX7400

You can modify your old transceivers and receivers, you need only
Stacked Dual Concentric Audio potentiometer and replace old potentiometer on AF or RF position. No drilling front panel !


Build up CW filter near new potentiometer


Spectrum of AF output of receiver with different mode of operation: LC filter + Switched-Capacitor AF Filter by MAX7400