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: http://www.phonestack.com/farhan/dc40.html 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.

The receiver will likely be described in the WIA's Amateur Radio magazine sometime in 2012.

Category:

Science & Technology

Tags:

• amateur
• homebrew
• QRP
• radio
• receiver
• direct
• conversion
• 40
• 20
• metres
• band
• HF

[superdallasdj]

at 2:49 speak italian, he say "cosa mi hai detto che non capisco"

[vk3ye]

@superdallasdj I did not understand that either!

[superdallasdj]

@vk3ye I know, sorry for my bad english

[vu2mue]

Awesome Peter

[59matta]

I have always enjoyed.

This particular receiver is very interesting.

I am also looking forward to the next.　７３！

JI1KZN

[mstax]

Another great DIY video, Peter! Very cool!

[llaven]

Fishing waves :-) please share schematic

[vk3crg]

Peter that receiver is a little ripper! Well done on yet another educational video. I like the way to explain what's in the box. Keep up the great work and I look forward to another QRP contact soon! 73, Craig VK3CRG

[G4AKC]

Another great video Peter, many thanks ....