Portable 40/20 metre direct conversion receiver

Trying a new 40 & 20 metre homebrew direct conversion portable receiver from various locations.

It was tested by the river early in the morning (not recorded here), a city park, by the beach and on a pier. Finally I try it from home, receiving G4AKC pedestrian mobile on 20 metres.

It uses 4 transistors and 1 IC. Incoming signals travel via a front end tuned circuit (peaked on either 7 or 14 MHz) to a NPN transistor RF preamp.

The local oscillator uses a 7.2 MHz ceramic resonator pulled over 7.040 - 7.240 MHz) to cover the SSB end of 40 metres (and 20 metres on harmonic). This signal goes to a FET buffer stage.

The incoming sigal and local oscillator are combined in a 4 diode doubly balanced product detector.

An NPN transistor preamp and LM386 amplify the audio. A 2.5 mH RF choke in series with the speaker can be switched in to provide top cut. This is amazingly simple but effective.

The band is changed by adjusting the front end tuning capacitor. I usually use 10 metres of wire as an antenna. It's primarily a 40 metre receiver, but as demonstrated by reception of G4AKC pedestrian mobile on 20 metres, it is also useful on that band as well.

Circuit of a very similar receiver: https://web.archive.org/web/201711090... The main differences are: 1. mine has a transistor RF amplifier but two fewer transistor in the audio section. 2. mine has a ceramic resonator local oscillator and 1 transistor buffer only.

A full constructional article for the receiver appeared in the WIA's Amateur Radio magazine November 2012, page 10. Please note that the 6.2v zener diode in the oscillator needs to be reversed for correct voltage regulation. Read it here: https://www.armag.vk6uu.id.au/2012-no...

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