A Simple Single Band Single Conversion Superhet
This is a single band, single conversion superheterodyne, receiver for the 60 meter shortwave broadcast band. It is a modern receiver with a synthesized local oscillator and a digital frequency display.
It was described in substantially more detail before the spam slam. Hopefully, sufficient information to successfully reproduce the receiver will be provided in this thread. The principal use of, and reason for construction of, this receiver is reception of the Legends on WRMI radio, 5050 KHz in early evenings, and 9455 KHz after midnight.
This receiver is intended to be suitable as a first superheterodyne project for novice builders. Shortcuts were taken in its design to accomplish this. In spite of the shortcuts, it works very well and is very satisfactory for its intended purpose.
This receiver is designed for reception of sixty (60) meters. Any shortwave band below 7.5 MHZ or so can be accommodated by redesign of the bandpass filter and adjustment of the tunable local oscillator frequency. Incoming RF signals are passed through a double tuned band pass filter centered at 5 MHZ, and then applied to a Mini Circuits SBL-1 diode double balanced mixer, that mixes down to an intermediate frequency of 462 KHz. (edit: a Mini Circuits ADE-1 is used here - an SBL-1 would work fine, but is a LOT larger.)
A MMBT3904 post mixer amplifier follows the mixer. Excellent Intermediate Frequency (“IF”) selectivity at 462 KHz is effected by a series combination of inexpensive and readily available Murata SFU455B ceramic filters.
A Philips TDA1072 integrated circuit provides IF amplification, Automatic Gain Control, AM detection, and low level audio amplification.
A Philips TDA7052A integrated circuit provides an electronic volume control, and loudspeaker lever audio power.
A simple “Raduino” - a portmanteau of radio and Arduino - provides tunable local oscillator injection. A Pro Mini Arduino clone controls a Si5351 oscillator and a simple LCD frequency display.
The radio is self contained in a compact 3D printed case that includes a 4 inch speaker. Further description will follow in subsequent posts.
A minor revision to reduce overall receiver RF gain, achieved by the easy, but dubious, method of just reducing the voltage to the IF amplifier.
Updated schematic attached.