Page last updated 24th April 2018
I've been working on an 80 metre receiver which is based on the circuit of the Elecraft K2. The front end, I.F. amplifier, AGC amplifier of my build is almost identical. However, I settled on 9MHz as the I.F. frequency after initially trying a 7.8MHz filter from a CB radio. The CB filter was a bit wide for my liking at 3.1 KHz or more. The 9MHz filter is about 2.4kHz wide.
An AD9850 DDS VFO was chosen for the local oscillator. The AD9850 is followed by an amplifier and a filter to achieve the required mixer injection level. Each section has been put on its own printed board and all mounted on a piece of scrap aluminium for testing. The results have been encouraging and I'll progress the project in some form as time permits.
The receiver's 80 metre bandpass filter was built on a separate PCB with the idea in mind to one day make this a multi-band receiver. The mixer is passive in the form of a Mini-Circuits SBL-1. An R.F. amplifier as well as an attenuator can be switched in or out of circuit via the two orange coloured relays.
The I.F. frequency is converted to a much lower frequency of 200KHz or so for the AGC amplifier. This reduces the potential for RF feedback in the 9 MHz I.F. amplifier.
The photo displayed below shows the current state of this project.