The fabulous German radio retro kits

These two kits implement single-frequency amplitude modulation radio receivers. I bought them online at www.conrad.fr
 

Simple retro radio kit :

It was a kit, I bought it online. So I had all the components along with a diagram and pictures ready in a box. Trying those kits is interesting because you get to see implemented basic radio techniques explained in books.

This is the most simple type of radio you can build. It uses amplitude modulation, which can carry less precise signal than FM but on greater distances and it is easier to implement.

Within the FM spectrum, waves travel in straight lines, unlike with the AM spectrum where longer waves are used. Longer waves can generally travel further. Inside the AM broadcast spectrum of frequencies, the highest frequencies (Short Waves) can be reflected by the ionosphere and thus "bounce" to propagate further. The Short waves AM stations are used to emit abroad. That's why AM enables you to receive radios from all over the world. I heard an North African radio and a Spanish radio with that kit, and with AM you can also generally get some BBC channels. Just from France.

The circuit is just an LC oscillator, where the solenoid acting as the antenna is coupled to a condensator in order to form an oscillator. C is variable, changing C also changes the resonnance frequency which determines the station you will hear. The circuit needs a redresser in the form of a diod. It includes transistors and extra resistances or condensators, in order to provide direct amplification. This is the component diagram in case you are interested :

Simple LC-oscillator AM receptor circuit

The antenna is actually a ferrite stick. Here is the kit once assembled :

Next...

Feedback radio retro kit :

This is the 2nd kit. Again, it all comes in the box, all I have to do is soldier everything. The funny thing is, those kits use really tiny PCBs, presumably making it easier to soldier. Well, it depends on your gear... As you can see on the following picture, all I had was a really big soldiering iron (45-60 W). Rather tough... Fortunately I had really tiny soldiering wire which made it all possible.

Feedback-amplification AM circuit

That was a real bitch to soldier. Fortunately I had my oh-so-versatile  assistant at hand, Chaussette (Sock but not suck please...) :

This kit is the implementation of a feedback-amplifier AM receptor. Same principle  as before, however this time the amplified signal comes back through a feedback circuit to affect the reception. The feedback element can be controlled via an extra potentiometer. Here is the component diagram :

Here is the assembled circuit :